Re: Fwd Bias LEDs as Varicaps/Varactors
A bench test, sort of...
Using a 30m Rx**, 10.116 crystal?and a BB910 vs a small LED
I adjusted the LED bias?for about the same measured?C range as the BB910
The read-out on my FT-847 Rx and 25Hz filter.
BB910?? 10.113000? 10.110850?? .002150? (10V)
LED???????10.116000? 10.113140?? .002860? (6.5V)
I want to do some measurements with sig gen and scope. Off hand, though, I'd say the LED is useable as a Varactor.
**Simple SA612/LM386? built for WWV-10 and 30m
--
Chuck, W5USJ (ex K2OFN)
Point, Rains Co, TX? EM22cv
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Re: Fwd Bias LEDs as Varicaps/Varactors
There is of course a nice exponential relationship between forward voltage and current.
But forward current is much easier to measure.
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On Sun, Dec 22, 2019 at 07:15 AM, Jerry Gaffke wrote:
so what the graph is really showing is capacitance as a function of forward current.
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Mike ? Yep, I have seen it there and plan to use for my6 builders.? The PC boards are coming from China based on some Gerbers I found.? But I did see a book at one of the web sites so I thought I would ask.? It’s a very nice thing that you have done putting those lesson up on your site, I appreciate it and your sited motivated me to get the boards built since you can not buy them anywhere and the PC board house that I used in China was cheap and very fast. ? Thanks so much for those lesson Mike ? Merry Christmas Steve NU0P ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Michael Maiorana
Sent: Sunday, December 22, 2019 5:19 AM
To: [email protected]
Subject: Re: [qrptech] Elmer 101 ? Steve, It's been over 20 years, but the original info is still on my qsl web page . You are welcome to print and use the info as you wish, just not for profit. ? On Sat, Dec 21, 2019, 10:03 PM stephen white <sswhite@...> wrote: I understand that their used to be a "Elmer 101" box available.? My little Builders group is going to be building SWxx's soon and would like to get a hold of this book for the builders.? Anyone have any ideas as to where I can get some of these or even one of these??? I have found all the Elmer 101 lessons on the net but if i can I would like to get the book.
Thanks
Steve NU0P
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Re: Fwd Bias LEDs as Varicaps/Varactors
Seeing a forward voltage of 12v applied across a 1n4001 got my attention as well.
From the webpage:? "NOTE: the voltages measured are at the wiper of the potentiometer, which is NOT now the voltage across the diode junction, since current is now flowing in the diode."
There's a 330k resistor in series with the diode under test, so what the graph is really showing is capacitance as a function of forward current.
The forward current through the diode is something on the order of (V-0.6)/330k
Jerry, KE7ER
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On Sun, Dec 22, 2019 at 06:55 AM, w8diz wrote:
Hi All, I gotta ask...
How can you forward bias a 1N4007 diode greater than 0.6 volts?
I must be missing something?
Diz
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Re: Fwd Bias LEDs as Varicaps/Varactors
It IS.
The "combined" graph had a hover feature to show forward bias
voltage, but it isn't working for me
either... if I am not mistaken...
73,
Gary
WB6OGD
On 12/22/2019 6:55 AM, w8diz wrote:
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Hi All, I gotta ask...
How can you forward bias a 1N4007 diode greater than 0.6 volts?
I must be missing something?
Diz
On 12/22/19 7:47 AM, Chuck Carpenter
wrote:
Read the Info from Hans,
And especially this comment with calculations at the
bottom...(Jerry)
Adam SQ5RWQ
Note that connecting two LEDs in series cuts C to 1/2.?
Also note that graph showing that C increases with voltage,
opposite of reverse bias and that C is much greater.? I tried
this with my tester with quite similar results.? Neat...
--
Chuck, W5USJ (ex K2OFN)
Point, Rains Co, TX? EM22cv
|
Re: Fwd Bias LEDs as Varicaps/Varactors
Hi All, I gotta ask...
How can you forward bias a 1N4007 diode greater than 0.6 volts?
I must be missing something?
Diz
On 12/22/19 7:47 AM, Chuck Carpenter
wrote:
toggle quoted message
Show quoted text
Read the Info from Hans,
And especially this comment with calculations at the
bottom...(Jerry)
Adam SQ5RWQ
Note that connecting two LEDs in series cuts C to 1/2.?
Also note that graph showing that C increases with voltage,
opposite of reverse bias and that C is much greater.? I tried this
with my tester with quite similar results.? Neat...
--
Chuck, W5USJ (ex K2OFN)
Point, Rains Co, TX? EM22cv
|
Thanks Richard,
I think Santa is bringing me a NanoVNA. I'm looking forward to learning what it can do for me.
Cheers,
Paul
VA3ZC
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Fwd Bias LEDs as Varicaps/Varactors
Read the Info from Hans,
And especially this comment with calculations at the bottom...(Jerry)
Adam SQ5RWQ
Note that connecting two LEDs in series cuts C to 1/2.? Also note that graph showing that C increases with voltage, opposite of reverse bias and that C is much greater.? I tried this with my tester with quite similar results.? Neat...
--
Chuck, W5USJ (ex K2OFN)
Point, Rains Co, TX? EM22cv
|
Steve, It's been over 20 years, but the original info is still on my qsl web page . You are welcome to print and use the info as you wish, just not for profit.
Good luck Mike Maiorana Ku4qo (ex kf4trd)
On Sat, Dec 21, 2019, 10:03 PM stephen white < sswhite@...> wrote: I understand that their used to be a "Elmer 101" box available.? My little Builders group is going to be building SWxx's soon and would like to get a hold of this book for the builders.? Anyone have any ideas as to where I can get some of these or even one of these??? I have found all the Elmer 101 lessons on the net but if i can I would like to get the book.
Thanks
Steve NU0P
|
Re: SMT Varactor vs Thru Hole
Eric,
Good info, makes sense when you relate the shape to functional applications.? On the O/T about the capacitor plates.? In my Vast Experience (or maybe Half-) I knew that tapered plate style as logarithmic and for the reason you mentioned.? And also, I'm rebuilding a z-match using dual 360pF poly caps. The plates in these little gems are of the tapered type making adjustment? a little smoother, I think...8^)
Not much happening with RMs? and RM][s?these days.?Rigs like the QCX have captured the interest with all the great features and functions at a good price.
Still...Fun Stuff
--
Chuck, W5USJ (ex K2OFN)
Point, Rains Co, TX? EM22cv
|
5% is 1.45uH so 0.6uH is well within tolerance. I've been analysing a 20m LPF with my NanoVNA and I found I had to remove a total of 4 turns off the 3 toroids to get a decent return loss and minimise the insertion loss. How tight the turns are and how spaced they are makes quite a difference.
--
73
Richard
G4TGJ
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QRPp journal Vol. IV No. 3
Cheers,
Mark.
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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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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)
?
|
I understand that their used to be a "Elmer 101" box available.? My little Builders group is going to be building SWxx's soon and would like to get a hold of this book for the builders.? Anyone have any ideas as to where I can get some of these or even one of these??? I have found all the Elmer 101 lessons on the net but if i can I would like to get the book.
Thanks
Steve NU0P
|
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)
?
|
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
|
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
|
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
|
Chuck Carpenter
Kirk Kleinschmidt, NT0Z