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Hello all,
I’m working on a prototype for a low cost magloop. ?Cost of ALL parts including WiFi/low energy Bluetooth “arduino-based” electronics and mechanical assembly for driving the capacitor is about $100 (no joke). ?Attached is a pic of the current prototype. ?It is mounted on some form board as a temporary support for testing, but I have plans to make this thing portable with a quick deployment system. ?The loop itself is 10mil 1 inch wide copper. ?Still working on the software, but It will self-tune and be manually controllable from an iPhone.
The capacitor is 3D printed from my own CAD design and still a work in progress. ?My current testing is confined to 20m, but I should be able to modify this thing to cover 10-30m at least...maybe 40...but I would rather have a 2nd loop for 40 thru 80.
?
The capacitor dialectic should handle at least 100W, but since I don't have a non-qrp radio in the house, I don’t know how stable it would be at that power...I plan to stress test this thing in the near future with the help of a non-qrp ham friend. ?It works well at qrp power.
I put it on 0.2 watts of WSPR today. ?My results:
Anyways...thought I would share. ?
73,
Kurt-AE6UJ
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I don't see anything recognizable as a cap in that photo, am curious how you are going about it.
Best guess is it's the metalic assembly above the PC board with coax in, a white wire coming out.
And the black thing under it is the motor drive?
I've never messed with a magnetic loop, but have considered it.
Was gluing formica type laminate to kitchen countertops here a few years ago,
part of it involved cutting long inch wide strips for the vertical edges with a table saw.
Occurred to me then I could glue copper foil to one side of such a laminate strip for a magloop.
And if the laminate proved to be a suitable dielectric for a capacitor, perhaps just overlap the ends,
compress that overlap to tune the resultant cap.? If not, then perhaps attach teflon (somehow)
to one end of the laminate strip for the capacitor dielectric.? The laminate bends easily enough,
a long strip could be wound into something a half meter in diameter for transport or storage.
Jerry, KE7ER
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Hey, Jerry,
Those are all great ideas...until you try them. :)
Mag loops don't work (well) unless we build them in ways that only mag loops require. Overlapping strip capacitors, as you describe, while they will "work" after a fashion, have huge losses in mag loop applications, and they don't stay stable with temperature and humidity, etc.
Loop conductors should be continuous and NEVER soldered. Capacitors should be vacuum variable or butterfly types with no mechanical wipers/contacts (huge losses). Mag loops in no way work like the antennas we're all used to, and different (weird?) construction techniques are required to make a good one.
Read this from Leigh, a VK5 expert in mag loop design and the underlying science. See:
There a lots of junky mag loops on Youtube, etc. They work -- as do 6-inch whip antennas -- just not very well.
There are some mag loop groups here on .io
Properly built mag loops are awesome. The opposite is also true :)
Good luck,
--Kirk, NT0Z ? Rochester, MN
My book, "Stealth Amateur Radio," is now available from
www.stealthamateur.com and on the Amazon Kindle (soon)
On Saturday, December 21, 2019, 3:12:13 PM CST, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
I don't see anything recognizable as a cap in that photo, am curious how you are going about it.
Best guess is it's the metalic assembly above the PC board with coax in, a white wire coming out.
And the black thing under it is the motor drive?
I've never messed with a magnetic loop, but have considered it.
Was gluing formica type laminate to kitchen countertops here a few years ago,
part of it involved cutting long inch wide strips for the vertical edges with a table saw.
Occurred to me then I could glue copper foil to one side of such a laminate strip for a magloop.
And if the laminate proved to be a suitable dielectric for a capacitor, perhaps just overlap the ends,
compress that overlap to tune the resultant cap.? If not, then perhaps attach teflon (somehow)
to one end of the laminate strip for the capacitor dielectric.? The laminate bends easily enough,
a long strip could be wound into something a half meter in diameter for transport or storage.
Jerry, KE7ER
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Hello Jerry,
There is more to this capacitor than meets the eye...but at its basics it is indeed controlled separation ?as a tuning mechanism...but dialectic choice is very important. ?Your formica dialectic wouldn’t work too well, I’m afraid. ?I once tried to make a loop something like this using a playing card as a dialectic and it didn’t work out too well. ? I learned about dialectic loss tangent after than experience.
One way you can tell that you have big losses in a mag loop is that you will have trouble getting a coupling loop to give you decent SWR without it being much larger than the typical 1/5 circumstance of the main loop...or you will need to make it a squished down oval close to the main loop. ? This antenna I show does have some loss, more than a several hundred dollar vacuum variable would give, but it is not too bad for my needs or most people’s needs I suspect. ?This antenna has a bandwidth of less than 40 kHz at 20 meters. ?Teflon is your friend. There is no soldering allowed in my design. ? ?The dirty secret of copper tubes is that everything inside the skin depth is a waste of money. ?My strip of copper here has more surface area than what is typically used by folks making it out of tubes...and it is easy to collapse.
The cap I show is actually breaking my long term rule for this loop. ?In my loop no metal other than the main loop and coupler is allowed above the feed point, but I am using metal push to fit connectors for my Teflon tuning drive in this prototype. ?I will 3D print these in the next prototype.?
The map I show of my WSPR receipts were from inside my house with the loop sitting on my kitchen table. ?But yeah...I’m sure others could do better.?
Kurt
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On Dec 21, 2019, at 3:12 PM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote: ?I don't see anything recognizable as a cap in that photo, am curious how you are going about it.
Best guess is it's the metalic assembly above the PC board with coax in, a white wire coming out.
And the black thing under it is the motor drive?
I've never messed with a magnetic loop, but have considered it.
Was gluing formica type laminate to kitchen countertops here a few years ago,
part of it involved cutting long inch wide strips for the vertical edges with a table saw.
Occurred to me then I could glue copper foil to one side of such a laminate strip for a magloop.
And if the laminate proved to be a suitable dielectric for a capacitor, perhaps just overlap the ends,
compress that overlap to tune the resultant cap.? If not, then perhaps attach teflon (somehow)
to one end of the laminate strip for the capacitor dielectric.? The laminate bends easily enough,
a long strip could be wound into something a half meter in diameter for transport or storage.
Jerry, KE7ER
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Looks like teflon has a sufficiently low loss tangent, is being used successfully as a dielectric on mag loops.
I'm sure a vacuum for the dielectric is preferred, but nothing costs way too much.
Could be compression, book, or trombone style, but having the cap be one piece with the copper loop
should be a win, assuming it can somehow be mechanically stable enough to stay tuned within a few khz.
Yes, it would be tough to get this to work well, currents are tens of amps, several kV across the cap.
But I don't yet see what is inherently wrong or inefficient with overlapping two strips of copper with a teflon dielectric.
?
No soldering between loop and cap?
That rules out most of the mag loop construction techniques I've seen.
And an argument to try overlapping the two ends of a copper strip to form a cap.
Jerry, KE7ER
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On Sat, Dec 21, 2019 at 01:29 PM, Kirk Kleinschmidt wrote:
Those are all great ideas...until you try them. :)
?
Mag loops don't work (well) unless we build them in ways that only mag loops require. Overlapping strip capacitors, as you describe, while they will "work" after a fashion, have huge losses in mag loop applications, and they don't stay stable with temperature and humidity, etc.
?
Loop conductors should be continuous and NEVER soldered. Capacitors should be vacuum variable or butterfly types with no mechanical wipers/contacts (huge losses). Mag loops in no way work like the antennas we're all used to, and different (weird?) construction techniques are required to make a good one.
?
Read this from Leigh, a VK5 expert in mag loop design and the underlying science. See:
?
There a lots of junky mag loops on Youtube, etc. They work -- as do 6-inch whip antennas -- just not very well.
?
There are some mag loop groups here on .io
?
Properly built mag loops are awesome. The opposite is also true :)
?
Good luck,
?
--Kirk, NT0Z
? Rochester, MN
?
My book, "Stealth Amateur Radio," is now available from www.stealthamateur.com and on the Amazon Kindle (soon)
?
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No solder...rule number one. ?
Rule number two...no metal other than the loop and coupler.
As far as stability. ?Great point and I can’t yet speak to power more than qrp. ?It works fine for qrp. ??
As far as higher power and stability? ?Looking forward to that exploration. ?If there is a stability issue at high power, it is likely a control problem that now days can be solved with some feedback systems, a $20 microcontroller, and some code. ?Active control. ?They fly bricks that shouldn’t in air now days that way...I’m just trying to make some QSOs from my kitchen table.
73,
Kurt?
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On Dec 21, 2019, at 8:57 PM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
?Looks like teflon has a sufficiently low loss tangent, is being used successfully as a dielectric on mag loops. I'm sure a vacuum for the dielectric is preferred, but nothing costs way too much. Could be compression, book, or trombone style, but having the cap be one piece with the copper loop should be a win, assuming it can somehow be mechanically stable enough to stay tuned within a few khz. Yes, it would be tough to get this to work well, currents are tens of amps, several kV across the cap. But I don't yet see what is inherently wrong or inefficient with overlapping two strips of copper with a teflon dielectric. ? No soldering between loop and cap? That rules out most of the mag loop construction techniques I've seen. And an argument to try overlapping the two ends of a copper strip to form a cap. Jerry, KE7ER On Sat, Dec 21, 2019 at 01:29 PM, Kirk Kleinschmidt wrote:
Those are all great ideas...until you try them. :)
?
Mag loops don't work (well) unless we build them in ways that only mag loops require. Overlapping strip capacitors, as you describe, while they will "work" after a fashion, have huge losses in mag loop applications, and they don't stay stable with temperature and humidity, etc.
?
Loop conductors should be continuous and NEVER soldered. Capacitors should be vacuum variable or butterfly types with no mechanical wipers/contacts (huge losses). Mag loops in no way work like the antennas we're all used to, and different (weird?) construction techniques are required to make a good one.
?
Read this from Leigh, a VK5 expert in mag loop design and the underlying science. See:
?
There a lots of junky mag loops on Youtube, etc. They work -- as do 6-inch whip antennas -- just not very well.
?
There are some mag loop groups here on .io
?
Properly built mag loops are awesome. The opposite is also true :)
?
Good luck,
?
--Kirk, NT0Z
? Rochester, MN
?
My book, "Stealth Amateur Radio," is now available from www.stealthamateur.com and on the Amazon Kindle (soon)
?
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Kurt is onto something with "no solder".
Tin-lead solder has 10x the resistivity of copper, tin-silver is not much better:
? ??
More of a difference than I would have expected.
I'm sure most amateur built mag loops are using solder.
Currents are so large in a high Q loop that even
a small fraction of an ohm makes a difference.
Would be interesting to evaluate solder vs no solder construction?of a mag-loop for efficiency.
There are plenty of competing naratives about how effective a mag loop is.
Things like the use of solder could definitely contribute to the disparity.
And a dielectric such as teflon that is usually very good might well be marginal in these conditions.
On the other hand, a thin film of solder at an overlap between two sheets of copper
would present a very short path for current flow through solder.
The shorter that path is (and the larger the area of overlap), the less impact it would have on resistance.
Even with 10x the inherent resistivity, the effect of such a junction should be much less than that of
the resistivity of the much longer path through the copper loop.
Jerry
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I still like that laminate strip with a copper foil glued to it, a teflon sheet for the dielectric?where the foil
overlaps?to form a cap.? The overlap is held firmly in place by a couple bare FR4 boards bolted onto it.?
Perhaps add a gimmick cap of a couple teflon covered wires across the overlap cap for final adjustments.
So a very limited tuning range once you bolt down the overlap cap, but good enough for?
hitting a digital watering hole or perhaps keeping a schedule on a particular frequency.?
From an online calculator, skin effect at 14mhz is around 18um (well under a thousandth of an inch) for copper.
So a strip of moderately thin copper foil on laminate is sufficient, very lightweight, winds down to a small diameter.
There are ways to make a good variable cap, I like the trombone scheme of QST Nov 1994.
Could simplify that by going to 1.5" copper pipe with a gear drive motor inside, a 1.25" pipe
covered by a teflon sheet being pulled into it by a motor driven screw, the loop flexes a bit as
the 1.25" pipe moves.? But that would take a week, the laminate plus foil might be working in a day.?
Lots of mag loops using teflon, is that considered good enough for the capacitor dielectric?
Will using laminate for mechanical support have some undesired effect?
Jerry, KE7ER
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The stability issue is real and controlling overlap with a motor is a challenge of engineering in and of itself. For myself I consider it a challenge and part of the fun.
Also...I have really come to believe that I don’t know how anyone builds a magloop or experiments with them without a proper antenna analyzer. I would be lost without mine. Not sure if you have one, but they make experimenting easier.
Kurt-ae6uj
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On Dec 22, 2019, at 3:09 PM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
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Yes, if bandwidth is maybe 10khz, mechanical stability will be a real concern.
My laminate thing, like a lot of mag loops I see, could be a bit floppy.
But perhaps an advantage, distort the circular shape to tune it?
Another thought about tuning, similar to a book cap, but uses FR4 board warping as a hinge:
Have two PCB's perhaps 2" x 12" of one sided copper, 3 inches of copper removed from one end of each.
The copper foil ends solder to each of the two PCB's at the ends that still have copper.
Place one board over the other with teflon in between with copper facing copper, the 3" of removed copper on opposite ends.
Two screws through one end hold them together firmly, the teflon well compressed here.
The other end has some sort of screw with spring arrangement to adjust the distance between the two boards there
If this is part of my foil on laminate antenna, could separate the two boards by removing those screws
when coiling the antenna up tight for transport.
nanoVNA here, but not yet dangerous with it.? Touch part of touch screen not working.
Need to spend a full day just figuring out the menu, or get NanoVNA-Saver going.
Also an AQRP VIA.
Agree on needing something more than a DVM.
Jerry
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On Sun, Dec 22, 2019 at 02:42 PM, Kurt Loken wrote:
The stability issue is real and controlling overlap with a motor is a challenge of engineering in and of itself. For myself I consider it a challenge and part of the fun.
Also...I have really come to believe that I don’t know how anyone builds a magloop or experiments with them without a proper antenna analyzer. I would be lost without mine. Not sure if you have one, but they make experimenting easier.
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Hello Jerry,
My 3D printed cap isn’t wholly dissimilar to what you describe. I think the stability issue could be mitigated by having an overlap system rather than a hinge but that causes complications because the diameter of the main loop is always going to change. One other thing I did consider with my cap is heat dissipation. What I ended up with is Teflon not just between but also around the overlapping ends. I would have rather build the capacitor surrounding structure out of ceramic, but by the time I did it that way I may as well buy a vacuum variable because the cost would be high.
Having fun is what this hobby should be about. It is also about learning by doing. There is a huge amount of information on magloops and you should read it all, but there are some very ingrained ideas that have become dogma. Dogma can be good...it fills up the pews...and most of it is right.
How small can you make an antenna and still have it work like a champ? That is one thing that intrigued me. What is the definition of working like a champ? Reaching Europe from your kitchen table?
Have fun,
Kurt-ae6uj
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On Dec 22, 2019, at 5:54 PM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
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Historically, Teflon hasn't been suitable for "daily drivers" over time, whether trombones or otherwise. It's fine for proof of concept, but it's far from ideal and it's lossy at RF. Not when used in "regular" antennas, but in magnetic loops, which are a whole nother breed.
What's been proven ideal? Vacuum and butterfly. That's pretty much it.
If you just want to crank out a "foxhole" loop, why not simply solder a short length or RG-8 coax (not foam dielectric, but the hard stuff) to the loop ends and cut the cable until the SWR analyzer says it's resonating on your chosen frequency? True, resonance moves around a bit with heat and humidity, but for single-frequency work it has been successfully used. And at 20 meters and up you'll have a few kHz of resonance to play around in.
I'm not trying to stifle innovation, but as an experienced mag loop builder and user (30 years now), I know that all of the things you're noodling around with have been tried before. The mag loop groups have treasure troves that detail what works and what doesn't. And of course, Youtube is filled with "revolutionary" loops that "work" after a fashion but absolutely don't work anywhere near as well as they could.
It takes about the same amount of farting around to make a mag loop that "works" as it does to use proven methods that are known to "work well" or define the state of the art.
Vacuum and Butterfly. Sounds like a country song! Or a mantra.
BTW, if you want an awesome autotuner designed for mag loops, complete with global temperature compensation, CAT and SWR inputs, and lots of other goodies, check out Loftur's masterpiece at:
Best of luck,
--Kirk, NT0Z
My book, "Stealth Amateur Radio," is now available from
www.stealthamateur.com and on the Amazon Kindle (soon)
On Sunday, December 22, 2019, 5:54:16 PM CST, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
Yes, if bandwidth is maybe 10khz, mechanical stability will be a real concern.
My laminate thing, like a lot of mag loops I see, could be a bit floppy.
But perhaps an advantage, distort the circular shape to tune it?
Another thought about tuning, similar to a book cap, but uses FR4 board warping as a hinge:
Have two PCB's perhaps 2" x 12" of one sided copper, 3 inches of copper removed from one end of each.
The copper foil ends solder to each of the two PCB's at the ends that still have copper.
Place one board over the other with teflon in between with copper facing copper, the 3" of removed copper on opposite ends.
Two screws through one end hold them together firmly, the teflon well compressed here.
The other end has some sort of screw with spring arrangement to adjust the distance between the two boards there
If this is part of my foil on laminate antenna, could separate the two boards by removing those screws
when coiling the antenna up tight for transport.
nanoVNA here, but not yet dangerous with it.? Touch part of touch screen not working.
Need to spend a full day just figuring out the menu, or get NanoVNA-Saver going.
Also an AQRP VIA.
Agree on needing something more than a DVM.
Jerry
On Sun, Dec 22, 2019 at 02:42 PM, Kurt Loken wrote:
The stability issue is real and controlling overlap with a motor is a challenge of engineering in and of itself. For myself I consider it a challenge and part of the fun.
Also...I have really come to believe that I don’t know how anyone builds a magloop or experiments with them without a proper antenna analyzer. I would be lost without mine. Not sure if you have one, but they make experimenting easier.
|
What do you mean by “daily drivers?” ?Can you also share some data that Teflon is lossy at rf?
Thanks for the help.
Kurt?
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On Dec 22, 2019, at 9:26 PM, Kirk Kleinschmidt via Groups.Io <sohosources@...> wrote:
? Historically, Teflon hasn't been suitable for "daily drivers" over time, whether trombones or otherwise. It's fine for proof of concept, but it's far from ideal and it's lossy at RF. Not when used in "regular" antennas, but in magnetic loops, which are a whole nother breed.
What's been proven ideal? Vacuum and butterfly. That's pretty much it.
If you just want to crank out a "foxhole" loop, why not simply solder a short length or RG-8 coax (not foam dielectric, but the hard stuff) to the loop ends and cut the cable until the SWR analyzer says it's resonating on your chosen frequency? True, resonance moves around a bit with heat and humidity, but for single-frequency work it has been successfully used. And at 20 meters and up you'll have a few kHz of resonance to play around in.
I'm not trying to stifle innovation, but as an experienced mag loop builder and user (30 years now), I know that all of the things you're noodling around with have been tried before. The mag loop groups have treasure troves that detail what works and what doesn't. And of course, Youtube is filled with "revolutionary" loops that "work" after a fashion but absolutely don't work anywhere near as well as they could.
It takes about the same amount of farting around to make a mag loop that "works" as it does to use proven methods that are known to "work well" or define the state of the art.
Vacuum and Butterfly. Sounds like a country song! Or a mantra.
BTW, if you want an awesome autotuner designed for mag loops, complete with global temperature compensation, CAT and SWR inputs, and lots of other goodies, check out Loftur's masterpiece at:
Best of luck,
--Kirk, NT0Z
My book, "Stealth Amateur Radio," is now available from
www.stealthamateur.com and on the Amazon Kindle (soon)
On Sunday, December 22, 2019, 5:54:16 PM CST, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
Yes, if bandwidth is maybe 10khz, mechanical stability will be a real concern. My laminate thing, like a lot of mag loops I see, could be a bit floppy. But perhaps an advantage, distort the circular shape to tune it? Another thought about tuning, similar to a book cap, but uses FR4 board warping as a hinge: Have two PCB's perhaps 2" x 12" of one sided copper, 3 inches of copper removed from one end of each. The copper foil ends solder to each of the two PCB's at the ends that still have copper. Place one board over the other with teflon in between with copper facing copper, the 3" of removed copper on opposite ends. Two screws through one end hold them together firmly, the teflon well compressed here. The other end has some sort of screw with spring arrangement to adjust the distance between the two boards there If this is part of my foil on laminate antenna, could separate the two boards by removing those screws when coiling the antenna up tight for transport. nanoVNA here, but not yet dangerous with it.? Touch part of touch screen not working. Need to spend a full day just figuring out the menu, or get NanoVNA-Saver going. Also an AQRP VIA. Agree on needing something more than a DVM. Jerry On Sun, Dec 22, 2019 at 02:42 PM, Kurt Loken wrote:
The stability issue is real and controlling overlap with a motor is a challenge of engineering in and of itself. For myself I consider it a challenge and part of the fun.
Also...I have really come to believe that I don’t know how anyone builds a magloop or experiments with them without a proper antenna analyzer. I would be lost without mine. Not sure if you have one, but they make experimenting easier.
|
That controller you link to is similar to what I have in mind...but an iPhone would be the interface to the user.
...but when I have someone with 30 years of knowledges telling me to give up...I’m at a loss of what to do. ? Am I wasting my time with the idea of building anything in my own? ?Can’t I just buy a commercial loop and save a lot of trouble. ?I think so. ?
Buy wire...hang a dipole.
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On Dec 22, 2019, at 10:36 PM, Kurt Loken via Groups.Io <kurt.loken@...> wrote: ? What do you mean by “daily drivers?” ?Can you also share some data that Teflon is lossy at rf?
Thanks for the help.
Kurt? On Dec 22, 2019, at 9:26 PM, Kirk Kleinschmidt via Groups.Io <sohosources@...> wrote:
? Historically, Teflon hasn't been suitable for "daily drivers" over time, whether trombones or otherwise. It's fine for proof of concept, but it's far from ideal and it's lossy at RF. Not when used in "regular" antennas, but in magnetic loops, which are a whole nother breed.
What's been proven ideal? Vacuum and butterfly. That's pretty much it.
If you just want to crank out a "foxhole" loop, why not simply solder a short length or RG-8 coax (not foam dielectric, but the hard stuff) to the loop ends and cut the cable until the SWR analyzer says it's resonating on your chosen frequency? True, resonance moves around a bit with heat and humidity, but for single-frequency work it has been successfully used. And at 20 meters and up you'll have a few kHz of resonance to play around in.
I'm not trying to stifle innovation, but as an experienced mag loop builder and user (30 years now), I know that all of the things you're noodling around with have been tried before. The mag loop groups have treasure troves that detail what works and what doesn't. And of course, Youtube is filled with "revolutionary" loops that "work" after a fashion but absolutely don't work anywhere near as well as they could.
It takes about the same amount of farting around to make a mag loop that "works" as it does to use proven methods that are known to "work well" or define the state of the art.
Vacuum and Butterfly. Sounds like a country song! Or a mantra.
BTW, if you want an awesome autotuner designed for mag loops, complete with global temperature compensation, CAT and SWR inputs, and lots of other goodies, check out Loftur's masterpiece at:
Best of luck,
--Kirk, NT0Z
My book, "Stealth Amateur Radio," is now available from
www.stealthamateur.com and on the Amazon Kindle (soon)
On Sunday, December 22, 2019, 5:54:16 PM CST, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
Yes, if bandwidth is maybe 10khz, mechanical stability will be a real concern. My laminate thing, like a lot of mag loops I see, could be a bit floppy. But perhaps an advantage, distort the circular shape to tune it? Another thought about tuning, similar to a book cap, but uses FR4 board warping as a hinge: Have two PCB's perhaps 2" x 12" of one sided copper, 3 inches of copper removed from one end of each. The copper foil ends solder to each of the two PCB's at the ends that still have copper. Place one board over the other with teflon in between with copper facing copper, the 3" of removed copper on opposite ends. Two screws through one end hold them together firmly, the teflon well compressed here. The other end has some sort of screw with spring arrangement to adjust the distance between the two boards there If this is part of my foil on laminate antenna, could separate the two boards by removing those screws when coiling the antenna up tight for transport. nanoVNA here, but not yet dangerous with it.? Touch part of touch screen not working. Need to spend a full day just figuring out the menu, or get NanoVNA-Saver going. Also an AQRP VIA. Agree on needing something more than a DVM. Jerry On Sun, Dec 22, 2019 at 02:42 PM, Kurt Loken wrote:
The stability issue is real and controlling overlap with a motor is a challenge of engineering in and of itself. For myself I consider it a challenge and part of the fun.
Also...I have really come to believe that I don’t know how anyone builds a magloop or experiments with them without a proper antenna analyzer. I would be lost without mine. Not sure if you have one, but they make experimenting easier.
|
Sorry, Kurt,
A "daily driver" is an antenna that stays in service for long periods of time and is used daily (as opposed to something whipped together for one reason or another). It's a motor vehicle reference. I guess I'm getting old!
The Teflon data I'm remembering is/was in the mag loop archives when everything was hosted on Yahoo Groups (may now be at groups,io?). I don't have access right now, as I'm traveling, but perhaps someone else is on both lists who might?
Because of the unusual electric and magnetic properties encountered by mag loop materials (30,000 V at 30 amps, anyone?), almost nothing other than vacuum and air variables with no physical contacts (butterfly caps) emerges as stable and non-lossy.
These and many additional materials have been tested over the past 50 years, not just by hams, but by the military and commercial companies developing the mag loops are related stuff.
Leigh, VK5KLT, who has been intimately involved in military and commercial mag loop design (and the underlying science) for the past 50 years, is an accessible and approachable authority on all details of materials, feeding and construction. He's a regular on the Mag Loop list, and his papers are available on the web. He emails, too.
What does Lee say about Teflon? He says that vacuum and butterfly caps are better. :)? Good enough for me.
I have worked up various trombone/Teflon approaches over the years, but after I studied a lot more I set them aside.
In short, it works, but it's not ideal.
Also, if I'm remembering the photo correctly, you may have had some wires running up one side of the mag loop from bottom to top? Consider centering these on the main axis of the loop, as maintaining loop balance can also be critical (hence the practice of splitting the loop down the center when running wires, installing motors and caps, etc). With massive circulating currents on the loop, objects that are closer to one side of the loop than the other can mess things up. The same goes for items in the environment (wires, trees dog houses, cars, air conditioners, etc).
Regards,
--Kirk, NT0Z
My book, "Stealth Amateur Radio," is now available from
www.stealthamateur.com and on the Amazon Kindle (soon)
On Sunday, December 22, 2019, 10:36:30 PM CST, Kurt Loken <kurt.loken@...> wrote:
What do you mean by “daily drivers?” ?Can you also share some data that Teflon is lossy at rf?
Thanks for the help.
Kurt?
On Dec 22, 2019, at 9:26 PM, Kirk Kleinschmidt via Groups.Io <sohosources@...> wrote:
? Historically, Teflon hasn't been suitable for "daily drivers" over time, whether trombones or otherwise. It's fine for proof of concept, but it's far from ideal and it's lossy at RF. Not when used in "regular" antennas, but in magnetic loops, which are a whole nother breed.
What's been proven ideal? Vacuum and butterfly. That's pretty much it.
If you just want to crank out a "foxhole" loop, why not simply solder a short length or RG-8 coax (not foam dielectric, but the hard stuff) to the loop ends and cut the cable until the SWR analyzer says it's resonating on your chosen frequency? True, resonance moves around a bit with heat and humidity, but for single-frequency work it has been successfully used. And at 20 meters and up you'll have a few kHz of resonance to play around in.
I'm not trying to stifle innovation, but as an experienced mag loop builder and user (30 years now), I know that all of the things you're noodling around with have been tried before. The mag loop groups have treasure troves that detail what works and what doesn't. And of course, Youtube is filled with "revolutionary" loops that "work" after a fashion but absolutely don't work anywhere near as well as they could.
It takes about the same amount of farting around to make a mag loop that "works" as it does to use proven methods that are known to "work well" or define the state of the art.
Vacuum and Butterfly. Sounds like a country song! Or a mantra.
BTW, if you want an awesome autotuner designed for mag loops, complete with global temperature compensation, CAT and SWR inputs, and lots of other goodies, check out Loftur's masterpiece at:
Best of luck,
--Kirk, NT0Z
My book, "Stealth Amateur Radio," is now available from
www.stealthamateur.com and on the Amazon Kindle (soon)
On Sunday, December 22, 2019, 5:54:16 PM CST, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
Yes, if bandwidth is maybe 10khz, mechanical stability will be a real concern. My laminate thing, like a lot of mag loops I see, could be a bit floppy. But perhaps an advantage, distort the circular shape to tune it? Another thought about tuning, similar to a book cap, but uses FR4 board warping as a hinge: Have two PCB's perhaps 2" x 12" of one sided copper, 3 inches of copper removed from one end of each. The copper foil ends solder to each of the two PCB's at the ends that still have copper. Place one board over the other with teflon in between with copper facing copper, the 3" of removed copper on opposite ends. Two screws through one end hold them together firmly, the teflon well compressed here. The other end has some sort of screw with spring arrangement to adjust the distance between the two boards there If this is part of my foil on laminate antenna, could separate the two boards by removing those screws when coiling the antenna up tight for transport. nanoVNA here, but not yet dangerous with it.? Touch part of touch screen not working. Need to spend a full day just figuring out the menu, or get NanoVNA-Saver going. Also an AQRP VIA. Agree on needing something more than a DVM. Jerry On Sun, Dec 22, 2019 at 02:42 PM, Kurt Loken wrote:
The stability issue is real and controlling overlap with a motor is a challenge of engineering in and of itself. For myself I consider it a challenge and part of the fun.
Also...I have really come to believe that I don’t know how anyone builds a magloop or experiments with them without a proper antenna analyzer. I would be lost without mine. Not sure if you have one, but they make experimenting easier.
|
I too am curious on the details of why teflon is not a good choice.
If so, homebrew air variable caps could work, they just have to be?
big enough for a suitable air gap.
It's a hobby, and an opportunity to learn.
If I just wanted to communicate a message with stuff I buy, I'd use a cell phone.
Or write a post to some web forum.
Jerry
|
Hello Kirk,
I think you might not be seeing what you think you are seeing.? I really made a big mistake posting here.? I wish I could delete my picture.? If anyone reading this knows how to delete photos from the group here, I would appreciate?help at making it so.? You get working on something and you want to share...but I'm not ready to share this stuff yet. ?
That "wire" on the side isn't a wire at all...it isn't what you think it is.? It will have zero effect on the loop...I guarantee it.? It is teflon and plastic not metal. ? There is NO METAL above the feed point other than those temporary push to fit connectors in the 3D printed cap.?
There are many choices that go into a design and one of them is cost.? Yes, a vacuum variable cannot be beat...though all the soldering of connections and all the peripherals (motors, shafts, etc.) that people seem to think are okay to put around them might lead to a debate on that subject.? There are some horrible designs on the internet...most of them have vac variables.? I am trying to make a low cost self tuning magloop with solid performance.? I think I can do that (including the electronics) for the cost of a single vac variable cap.? I would think this would interest someone who writes about stealth antennas.?
Teflon is not lossy in rf.? What material beats it?? Polystyrene?? Not much else. ?
The loop I'm making I also intend to use indoors, it is not meant to be used permanently mounted outside. ?
This map I show below were confirmed receipts yesterday of my 0.2W transmission from the loop in the picture sitting where the picture was taken...on my kitchen table.? I have reached hawaii and europe from that table using 0.2 watts on other days. ? No whip antenna would do that...feel free to try and let us know how it works out.
Kurt-ae6uj ???
On Sun, Dec 22, 2019 at 11:08 PM Kirk Kleinschmidt via Groups.Io <sohosources= [email protected]> wrote: Sorry, Kurt,
A "daily driver" is an antenna that stays in service for long periods of time and is used daily (as opposed to something whipped together for one reason or another). It's a motor vehicle reference. I guess I'm getting old!
The Teflon data I'm remembering is/was in the mag loop archives when everything was hosted on Yahoo Groups (may now be at groups,io?). I don't have access right now, as I'm traveling, but perhaps someone else is on both lists who might?
Because of the unusual electric and magnetic properties encountered by mag loop materials (30,000 V at 30 amps, anyone?), almost nothing other than vacuum and air variables with no physical contacts (butterfly caps) emerges as stable and non-lossy.
These and many additional materials have been tested over the past 50 years, not just by hams, but by the military and commercial companies developing the mag loops are related stuff.
Leigh, VK5KLT, who has been intimately involved in military and commercial mag loop design (and the underlying science) for the past 50 years, is an accessible and approachable authority on all details of materials, feeding and construction. He's a regular on the Mag Loop list, and his papers are available on the web. He emails, too.
What does Lee say about Teflon? He says that vacuum and butterfly caps are better. :)? Good enough for me.
I have worked up various trombone/Teflon approaches over the years, but after I studied a lot more I set them aside.
In short, it works, but it's not ideal.
Also, if I'm remembering the photo correctly, you may have had some wires running up one side of the mag loop from bottom to top? Consider centering these on the main axis of the loop, as maintaining loop balance can also be critical (hence the practice of splitting the loop down the center when running wires, installing motors and caps, etc). With massive circulating currents on the loop, objects that are closer to one side of the loop than the other can mess things up. The same goes for items in the environment (wires, trees dog houses, cars, air conditioners, etc).
Regards,
--Kirk, NT0Z
My book, "Stealth Amateur Radio," is now available from
and on the Amazon Kindle (soon)
On Sunday, December 22, 2019, 10:36:30 PM CST, Kurt Loken < kurt.loken@...> wrote:
What do you mean by “daily drivers?” ?Can you also share some data that Teflon is lossy at rf?
Thanks for the help.
Kurt? On Dec 22, 2019, at 9:26 PM, Kirk Kleinschmidt via Groups.Io <sohosources=[email protected]> wrote:
? Historically, Teflon hasn't been suitable for "daily drivers" over time, whether trombones or otherwise. It's fine for proof of concept, but it's far from ideal and it's lossy at RF. Not when used in "regular" antennas, but in magnetic loops, which are a whole nother breed.
What's been proven ideal? Vacuum and butterfly. That's pretty much it.
If you just want to crank out a "foxhole" loop, why not simply solder a short length or RG-8 coax (not foam dielectric, but the hard stuff) to the loop ends and cut the cable until the SWR analyzer says it's resonating on your chosen frequency? True, resonance moves around a bit with heat and humidity, but for single-frequency work it has been successfully used. And at 20 meters and up you'll have a few kHz of resonance to play around in.
I'm not trying to stifle innovation, but as an experienced mag loop builder and user (30 years now), I know that all of the things you're noodling around with have been tried before. The mag loop groups have treasure troves that detail what works and what doesn't. And of course, Youtube is filled with "revolutionary" loops that "work" after a fashion but absolutely don't work anywhere near as well as they could.
It takes about the same amount of farting around to make a mag loop that "works" as it does to use proven methods that are known to "work well" or define the state of the art.
Vacuum and Butterfly. Sounds like a country song! Or a mantra.
BTW, if you want an awesome autotuner designed for mag loops, complete with global temperature compensation, CAT and SWR inputs, and lots of other goodies, check out Loftur's masterpiece at:
Best of luck,
--Kirk, NT0Z
My book, "Stealth Amateur Radio," is now available from
and on the Amazon Kindle (soon)
On Sunday, December 22, 2019, 5:54:16 PM CST, Jerry Gaffke via Groups.Io <jgaffke= [email protected]> wrote:
Yes, if bandwidth is maybe 10khz, mechanical stability will be a real concern. My laminate thing, like a lot of mag loops I see, could be a bit floppy. But perhaps an advantage, distort the circular shape to tune it? Another thought about tuning, similar to a book cap, but uses FR4 board warping as a hinge: Have two PCB's perhaps 2" x 12" of one sided copper, 3 inches of copper removed from one end of each. The copper foil ends solder to each of the two PCB's at the ends that still have copper. Place one board over the other with teflon in between with copper facing copper, the 3" of removed copper on opposite ends. Two screws through one end hold them together firmly, the teflon well compressed here. The other end has some sort of screw with spring arrangement to adjust the distance between the two boards there If this is part of my foil on laminate antenna, could separate the two boards by removing those screws when coiling the antenna up tight for transport. nanoVNA here, but not yet dangerous with it.? Touch part of touch screen not working. Need to spend a full day just figuring out the menu, or get NanoVNA-Saver going. Also an AQRP VIA. Agree on needing something more than a DVM. Jerry On Sun, Dec 22, 2019 at 02:42 PM, Kurt Loken wrote:
The stability issue is real and controlling overlap with a motor is a challenge of engineering in and of itself. For myself I consider it a challenge and part of the fun.
Also...I have really come to believe that I don’t know how anyone builds a magloop or experiments with them without a proper antenna analyzer. I would be lost without mine. Not sure if you have one, but they make experimenting easier.
|
I get it. I'm not trying to stifle experimentation. I simply want to steer you toward the best resources.
Self-resonant mag loops made from strap (where the insulated ends overlap to provide the C to the loop's L), work best at VHF, where the high Q of the antenna still provides enough low-SWR bandwidth around the resonance point to minimize the effects of insulation-induced instabilities (temperature and humidity effects, too).
At 160 and 80 meters, however, when bandwidths are 3-5 kHz, more stable materials are beneficial or necessary.
Using WSPR to reference/define antenna performance is somewhat moot unless all you want to do is WSPR, at which point making a useful antenna becomes 40-dB "easier" than if you're trying to make an antenna that will be used for more conversational or more conventional modes. I congratulate you, but working DX via WSPR with any mag loop, even indoors or in the basement, is the norm and not the exception. If you run the numbers regarding propagation path loss, antenna gain, and the sensitivity of the WSPR demodulation process, you'll see that those distances are expected and on track. To make those QSOs via SSB, CW, or even PSK-31 takes a better-performing antenna/mag loop or more RF power, but it is still doable, even indoors. Many mag loop users, myself included, have made ocean-hopping SSB QSOs with mag loops sitting on the kitchen table while running QRP (5-10 W PEP) Again, scaling the numbers for power and the efficiency of the WSPR decoder, the events are approximately equivalent.
I don't know how to remove posted pix. Maybe it's not even possible.
Regardless, I'm just having a conversation here, so don't let me get in your way. I think what you're doing is fantastic. I have been doing my best to steer you toward the best methods and materials, but personal experimentation always earns my respect. Other readers, perhaps lacking your skills and determination, may want to know about what experts and experimenters have already discovered about how to make top-performing mag loops and mag loop autotuners. I have provided those links and references as part of our conversation.
Regards,
--Kirk, NT0Z ? Rochester, MN
My book, "Stealth Amateur Radio," is now available from
www.stealthamateur.com and on the Amazon Kindle (soon)
On Monday, December 23, 2019, 12:05:52 AM CST, Kurt Loken <kurt.loken@...> wrote:
Hello Kirk,
I think you might not be seeing what you think you are seeing.? I really made a big mistake posting here.? I wish I could delete my picture.? If anyone reading this knows how to delete photos from the group here, I would appreciate?help at making it so.? You get working on something and you want to share...but I'm not ready to share this stuff yet. ?
That "wire" on the side isn't a wire at all...it isn't what you think it is.? It will have zero effect on the loop...I guarantee it.? It is teflon and plastic not metal. ? There is NO METAL above the feed point other than those temporary push to fit connectors in the 3D printed cap.?
There are many choices that go into a design and one of them is cost.? Yes, a vacuum variable cannot be beat...though all the soldering of connections and all the peripherals (motors, shafts, etc.) that people seem to think are okay to put around them might lead to a debate on that subject.? There are some horrible designs on the internet...most of them have vac variables.? I am trying to make a low cost self tuning magloop with solid performance.? I think I can do that (including the electronics) for the cost of a single vac variable cap.? I would think this would interest someone who writes about stealth antennas.?
Teflon is not lossy in rf.? What material beats it?? Polystyrene?? Not much else. ?
The loop I'm making I also intend to use indoors, it is not meant to be used permanently mounted outside. ?
This map I show below were confirmed receipts yesterday of my 0.2W transmission from the loop in the picture sitting where the picture was taken...on my kitchen table.? I have reached hawaii and europe from that table using 0.2 watts on other days. ? No whip antenna would do that...feel free to try and let us know how it works out.
Kurt-ae6uj ???
On Sun, Dec 22, 2019 at 11:08 PM Kirk Kleinschmidt via Groups.Io <sohosources= [email protected]> wrote: Sorry, Kurt,
A "daily driver" is an antenna that stays in service for long periods of time and is used daily (as opposed to something whipped together for one reason or another). It's a motor vehicle reference. I guess I'm getting old!
The Teflon data I'm remembering is/was in the mag loop archives when everything was hosted on Yahoo Groups (may now be at groups,io?). I don't have access right now, as I'm traveling, but perhaps someone else is on both lists who might?
Because of the unusual electric and magnetic properties encountered by mag loop materials (30,000 V at 30 amps, anyone?), almost nothing other than vacuum and air variables with no physical contacts (butterfly caps) emerges as stable and non-lossy.
These and many additional materials have been tested over the past 50 years, not just by hams, but by the military and commercial companies developing the mag loops are related stuff.
Leigh, VK5KLT, who has been intimately involved in military and commercial mag loop design (and the underlying science) for the past 50 years, is an accessible and approachable authority on all details of materials, feeding and construction. He's a regular on the Mag Loop list, and his papers are available on the web. He emails, too.
What does Lee say about Teflon? He says that vacuum and butterfly caps are better. :)? Good enough for me.
I have worked up various trombone/Teflon approaches over the years, but after I studied a lot more I set them aside.
In short, it works, but it's not ideal.
Also, if I'm remembering the photo correctly, you may have had some wires running up one side of the mag loop from bottom to top? Consider centering these on the main axis of the loop, as maintaining loop balance can also be critical (hence the practice of splitting the loop down the center when running wires, installing motors and caps, etc). With massive circulating currents on the loop, objects that are closer to one side of the loop than the other can mess things up. The same goes for items in the environment (wires, trees dog houses, cars, air conditioners, etc).
Regards,
--Kirk, NT0Z
My book, "Stealth Amateur Radio," is now available from
and on the Amazon Kindle (soon)
On Sunday, December 22, 2019, 10:36:30 PM CST, Kurt Loken < kurt.loken@...> wrote:
What do you mean by “daily drivers?” ?Can you also share some data that Teflon is lossy at rf?
Thanks for the help.
Kurt? On Dec 22, 2019, at 9:26 PM, Kirk Kleinschmidt via Groups.Io <sohosources=[email protected]> wrote:
? Historically, Teflon hasn't been suitable for "daily drivers" over time, whether trombones or otherwise. It's fine for proof of concept, but it's far from ideal and it's lossy at RF. Not when used in "regular" antennas, but in magnetic loops, which are a whole nother breed.
What's been proven ideal? Vacuum and butterfly. That's pretty much it.
If you just want to crank out a "foxhole" loop, why not simply solder a short length or RG-8 coax (not foam dielectric, but the hard stuff) to the loop ends and cut the cable until the SWR analyzer says it's resonating on your chosen frequency? True, resonance moves around a bit with heat and humidity, but for single-frequency work it has been successfully used. And at 20 meters and up you'll have a few kHz of resonance to play around in.
I'm not trying to stifle innovation, but as an experienced mag loop builder and user (30 years now), I know that all of the things you're noodling around with have been tried before. The mag loop groups have treasure troves that detail what works and what doesn't. And of course, Youtube is filled with "revolutionary" loops that "work" after a fashion but absolutely don't work anywhere near as well as they could.
It takes about the same amount of farting around to make a mag loop that "works" as it does to use proven methods that are known to "work well" or define the state of the art.
Vacuum and Butterfly. Sounds like a country song! Or a mantra.
BTW, if you want an awesome autotuner designed for mag loops, complete with global temperature compensation, CAT and SWR inputs, and lots of other goodies, check out Loftur's masterpiece at:
Best of luck,
--Kirk, NT0Z
My book, "Stealth Amateur Radio," is now available from
and on the Amazon Kindle (soon)
On Sunday, December 22, 2019, 5:54:16 PM CST, Jerry Gaffke via Groups.Io <jgaffke= [email protected]> wrote:
Yes, if bandwidth is maybe 10khz, mechanical stability will be a real concern. My laminate thing, like a lot of mag loops I see, could be a bit floppy. But perhaps an advantage, distort the circular shape to tune it? Another thought about tuning, similar to a book cap, but uses FR4 board warping as a hinge: Have two PCB's perhaps 2" x 12" of one sided copper, 3 inches of copper removed from one end of each. The copper foil ends solder to each of the two PCB's at the ends that still have copper. Place one board over the other with teflon in between with copper facing copper, the 3" of removed copper on opposite ends. Two screws through one end hold them together firmly, the teflon well compressed here. The other end has some sort of screw with spring arrangement to adjust the distance between the two boards there If this is part of my foil on laminate antenna, could separate the two boards by removing those screws when coiling the antenna up tight for transport. nanoVNA here, but not yet dangerous with it.? Touch part of touch screen not working. Need to spend a full day just figuring out the menu, or get NanoVNA-Saver going. Also an AQRP VIA. Agree on needing something more than a DVM. Jerry On Sun, Dec 22, 2019 at 02:42 PM, Kurt Loken wrote:
The stability issue is real and controlling overlap with a motor is a challenge of engineering in and of itself. For myself I consider it a challenge and part of the fun.
Also...I have really come to believe that I don’t know how anyone builds a magloop or experiments with them without a proper antenna analyzer. I would be lost without mine. Not sure if you have one, but they make experimenting easier.
|
Well hell...you are telling me I could have done all this work in my basement and not the kitchen table? ?Wow. ?My wife will be happy to hear that. ? They really have a racket going to claim WSPR is good for antenna testing. ?Do you have a chapter in your book on that? ?You need to get the word out that is a worthless testing tool.
I am not designing my loop for 80 and 160. ?
I don’t know what you “get” or what your game is, but you make a lot of assumptions. ?it is amusing you show me a link to a controller that has an option for tracking its tuning to SWR and then you give me a story about how instability is insurmountable. ? Got it.
toggle quoted message
Show quoted text
On Dec 23, 2019, at 1:37 AM, Kirk Kleinschmidt via Groups.Io <sohosources@...> wrote:
? I get it. I'm not trying to stifle experimentation. I simply want to steer you toward the best resources.
Self-resonant mag loops made from strap (where the insulated ends overlap to provide the C to the loop's L), work best at VHF, where the high Q of the antenna still provides enough low-SWR bandwidth around the resonance point to minimize the effects of insulation-induced instabilities (temperature and humidity effects, too).
At 160 and 80 meters, however, when bandwidths are 3-5 kHz, more stable materials are beneficial or necessary.
Using WSPR to reference/define antenna performance is somewhat moot unless all you want to do is WSPR, at which point making a useful antenna becomes 40-dB "easier" than if you're trying to make an antenna that will be used for more conversational or more conventional modes. I congratulate you, but working DX via WSPR with any mag loop, even indoors or in the basement, is the norm and not the exception. If you run the numbers regarding propagation path loss, antenna gain, and the sensitivity of the WSPR demodulation process, you'll see that those distances are expected and on track. To make those QSOs via SSB, CW, or even PSK-31 takes a better-performing antenna/mag loop or more RF power, but it is still doable, even indoors. Many mag loop users, myself included, have made ocean-hopping SSB QSOs with mag loops sitting on the kitchen table while running QRP (5-10 W PEP) Again, scaling the numbers for power and the efficiency of the WSPR decoder, the events are approximately equivalent.
I don't know how to remove posted pix. Maybe it's not even possible.
Regardless, I'm just having a conversation here, so don't let me get in your way. I think what you're doing is fantastic. I have been doing my best to steer you toward the best methods and materials, but personal experimentation always earns my respect. Other readers, perhaps lacking your skills and determination, may want to know about what experts and experimenters have already discovered about how to make top-performing mag loops and mag loop autotuners. I have provided those links and references as part of our conversation.
Regards,
--Kirk, NT0Z ? Rochester, MN
My book, "Stealth Amateur Radio," is now available from
www.stealthamateur.com and on the Amazon Kindle (soon)
On Monday, December 23, 2019, 12:05:52 AM CST, Kurt Loken <kurt.loken@...> wrote:
Hello Kirk,
I think you might not be seeing what you think you are seeing.? I really made a big mistake posting here.? I wish I could delete my picture.? If anyone reading this knows how to delete photos from the group here, I would appreciate?help at making it so.? You get working on something and you want to share...but I'm not ready to share this stuff yet. ?
That "wire" on the side isn't a wire at all...it isn't what you think it is.? It will have zero effect on the loop...I guarantee it.? It is teflon and plastic not metal. ? There is NO METAL above the feed point other than those temporary push to fit connectors in the 3D printed cap.?
There are many choices that go into a design and one of them is cost.? Yes, a vacuum variable cannot be beat...though all the soldering of connections and all the peripherals (motors, shafts, etc.) that people seem to think are okay to put around them might lead to a debate on that subject.? There are some horrible designs on the internet...most of them have vac variables.? I am trying to make a low cost self tuning magloop with solid performance.? I think I can do that (including the electronics) for the cost of a single vac variable cap.? I would think this would interest someone who writes about stealth antennas.?
Teflon is not lossy in rf.? What material beats it?? Polystyrene?? Not much else. ?
The loop I'm making I also intend to use indoors, it is not meant to be used permanently mounted outside. ?
This map I show below were confirmed receipts yesterday of my 0.2W transmission from the loop in the picture sitting where the picture was taken...on my kitchen table.? I have reached hawaii and europe from that table using 0.2 watts on other days. ? No whip antenna would do that...feel free to try and let us know how it works out.
<Screen Shot 2019-12-21 at 1.36.55 PM.png>
Kurt-ae6uj ???
On Sun, Dec 22, 2019 at 11:08 PM Kirk Kleinschmidt via Groups.Io <sohosources= [email protected]> wrote: Sorry, Kurt,
A "daily driver" is an antenna that stays in service for long periods of time and is used daily (as opposed to something whipped together for one reason or another). It's a motor vehicle reference. I guess I'm getting old!
The Teflon data I'm remembering is/was in the mag loop archives when everything was hosted on Yahoo Groups (may now be at groups,io?). I don't have access right now, as I'm traveling, but perhaps someone else is on both lists who might?
Because of the unusual electric and magnetic properties encountered by mag loop materials (30,000 V at 30 amps, anyone?), almost nothing other than vacuum and air variables with no physical contacts (butterfly caps) emerges as stable and non-lossy.
These and many additional materials have been tested over the past 50 years, not just by hams, but by the military and commercial companies developing the mag loops are related stuff.
Leigh, VK5KLT, who has been intimately involved in military and commercial mag loop design (and the underlying science) for the past 50 years, is an accessible and approachable authority on all details of materials, feeding and construction. He's a regular on the Mag Loop list, and his papers are available on the web. He emails, too.
What does Lee say about Teflon? He says that vacuum and butterfly caps are better. :)? Good enough for me.
I have worked up various trombone/Teflon approaches over the years, but after I studied a lot more I set them aside.
In short, it works, but it's not ideal.
Also, if I'm remembering the photo correctly, you may have had some wires running up one side of the mag loop from bottom to top? Consider centering these on the main axis of the loop, as maintaining loop balance can also be critical (hence the practice of splitting the loop down the center when running wires, installing motors and caps, etc). With massive circulating currents on the loop, objects that are closer to one side of the loop than the other can mess things up. The same goes for items in the environment (wires, trees dog houses, cars, air conditioners, etc).
Regards,
--Kirk, NT0Z
My book, "Stealth Amateur Radio," is now available from
and on the Amazon Kindle (soon)
On Sunday, December 22, 2019, 10:36:30 PM CST, Kurt Loken < kurt.loken@...> wrote:
What do you mean by “daily drivers?” ?Can you also share some data that Teflon is lossy at rf?
Thanks for the help.
Kurt? On Dec 22, 2019, at 9:26 PM, Kirk Kleinschmidt via Groups.Io <sohosources=[email protected]> wrote:
? Historically, Teflon hasn't been suitable for "daily drivers" over time, whether trombones or otherwise. It's fine for proof of concept, but it's far from ideal and it's lossy at RF. Not when used in "regular" antennas, but in magnetic loops, which are a whole nother breed.
What's been proven ideal? Vacuum and butterfly. That's pretty much it.
If you just want to crank out a "foxhole" loop, why not simply solder a short length or RG-8 coax (not foam dielectric, but the hard stuff) to the loop ends and cut the cable until the SWR analyzer says it's resonating on your chosen frequency? True, resonance moves around a bit with heat and humidity, but for single-frequency work it has been successfully used. And at 20 meters and up you'll have a few kHz of resonance to play around in.
I'm not trying to stifle innovation, but as an experienced mag loop builder and user (30 years now), I know that all of the things you're noodling around with have been tried before. The mag loop groups have treasure troves that detail what works and what doesn't. And of course, Youtube is filled with "revolutionary" loops that "work" after a fashion but absolutely don't work anywhere near as well as they could.
It takes about the same amount of farting around to make a mag loop that "works" as it does to use proven methods that are known to "work well" or define the state of the art.
Vacuum and Butterfly. Sounds like a country song! Or a mantra.
BTW, if you want an awesome autotuner designed for mag loops, complete with global temperature compensation, CAT and SWR inputs, and lots of other goodies, check out Loftur's masterpiece at:
Best of luck,
--Kirk, NT0Z
My book, "Stealth Amateur Radio," is now available from
and on the Amazon Kindle (soon)
On Sunday, December 22, 2019, 5:54:16 PM CST, Jerry Gaffke via Groups.Io <jgaffke= [email protected]> wrote:
Yes, if bandwidth is maybe 10khz, mechanical stability will be a real concern. My laminate thing, like a lot of mag loops I see, could be a bit floppy. But perhaps an advantage, distort the circular shape to tune it? Another thought about tuning, similar to a book cap, but uses FR4 board warping as a hinge: Have two PCB's perhaps 2" x 12" of one sided copper, 3 inches of copper removed from one end of each. The copper foil ends solder to each of the two PCB's at the ends that still have copper. Place one board over the other with teflon in between with copper facing copper, the 3" of removed copper on opposite ends. Two screws through one end hold them together firmly, the teflon well compressed here. The other end has some sort of screw with spring arrangement to adjust the distance between the two boards there If this is part of my foil on laminate antenna, could separate the two boards by removing those screws when coiling the antenna up tight for transport. nanoVNA here, but not yet dangerous with it.? Touch part of touch screen not working. Need to spend a full day just figuring out the menu, or get NanoVNA-Saver going. Also an AQRP VIA. Agree on needing something more than a DVM. Jerry On Sun, Dec 22, 2019 at 02:42 PM, Kurt Loken wrote:
The stability issue is real and controlling overlap with a motor is a challenge of engineering in and of itself. For myself I consider it a challenge and part of the fun.
Also...I have really come to believe that I don’t know how anyone builds a magloop or experiments with them without a proper antenna analyzer. I would be lost without mine. Not sure if you have one, but they make experimenting easier.
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Kirk Kleinschmidt, NT0Z