Re: Reasonable size of an AziLoop?
I currently have an Azi-Loop in the construction process; Thanks Guy, I know your and Walt's ambitions for AM-DX, your solution is already very perfect. I can see that the size (one meter up or down) will be a very good option, also the self-supporting structure is a perfect solution, especially because of animals. I'm already looking forward to a short report on the antenna from your upcoming DXpedtion. My plan is to erect the antenna in the summer, just in time before the first Asian signals can be heard in Central Europe in the fall. Thanks also for the photo, very helpful. Good luck with the AziLoop on your DXpedtion! 73 Christoph, OE2CRM —
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Re: "active antenna preamplifiers" in ham radio May 1986
The J-310 would be a much better choice. ??
Dave - W?LEV
With todays knowledge, the usage of a MOSFETs in the front stage of an active e-field impedance converter is not really a good idea. Even if some professional active-monopoles like the Eastern German KAA1000 with its made-in-Russia KP902A Power-MOSFET went this way in the past. The noise of as MOSFET is much higher compared to a JFET.? You should also avoid a series resistors to the gate or keep it as small as possible, its thermal noise voltage adds to the signal and degrades the noise figure. That 's why i would not recommend the fig.2 circuit in this article.
?
regards
Fred
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Re: Reasonable size of an AziLoop?
Hi Christoph,
I use 16m (50ft) circumference (W=20ft, top H=15ft, bottom H=4ft) .? I decided on this size for 9dB or 10dB noise over-ride from the antenna on 160m. using only 4 x 3.5m elevated radials (H=3ft) as a counterpoise.
In K9AY loop mode, the antenna works very well on MW as well as 160m and 80m., with measured groundwave f/b in the region of 30dB, degrading considerably on 7 and 10MHz..
The sensitivity of the antenna models just over -40dBi with the counterpoise, and -35dBi if a good conventional earth is used.
?
So with a good conventional earth you may be able to go considerably smaller than 16m. which will help the antenna performance on higher frequencies where the K9AY cardioid pattern degrades. Quickly modelling a size reduction for near -40dBi on 1.8MHz indicates about 10.5m circumference. However, there is considerable difference in back-lobe pattern using the two earth systems, with a high null (around 45 degrees) using the conventional earth but less groundwave null.
?
In performance, the Aziloop is up to a few dB down in s/n on my beverages in their optimum directions on some days, as we might expect from their comparative RDFs, but this depends on direction and conditions of course. I can hardly rotate a 200m wire - !!? Also when the ionoshere favours higher angles then the Aziloop is just as good, again as you might expect from the comparitive patterns.
73
John
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Re: Added photo album Azi-Loop Self-Supporting Structure for Transportable / DXpedition Use
#photo-notice
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Re: "active antenna preamplifiers" in ham radio May 1986
With todays knowledge, the usage of a MOSFETs in the front stage of an active e-field impedance converter is not really a good idea. Even if some professional active-monopoles like the Eastern German KAA1000 with its made-in-Russia KP902A Power-MOSFET went this way in the past. The noise of as MOSFET is much higher compared to a JFET.? You should also avoid a series resistors to the gate or keep it as small as possible, its thermal noise voltage adds to the signal and degrades the noise figure. That 's why i would not recommend the fig.2 circuit in this article.
?
regards
Fred
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Re: "active antenna preamplifiers" in ham radio May 1986
Hi Hisami,
?
The circuit and principles shown in the article are valid, but the reasoning behind them is now somewhat dated. The use of a power FET for this purpose was "state of the Art" at the time of publication, but IMHO has since been superseded.
?
Power FET's tended to present a very high value of input capacitance, which is less than ideal when used with a short? "whip" antenna. The Intermodulation performance of the amplifier in the article is also worse than I would expect to be able to obtain by using more recent devices. Many of the techniques mentioned in the article are attempts to improve these parameters, which are less problematic in modern designs.
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Unless you are interested in reception at very low frequencies, say <100kHz, it is not necessary to use an amplifier with a very high value of input resistance. By reducing this value, it is possible to relax the design parameters, whilst still being capable of producing good results.
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On Wed, Mar 12, 2025 at 04:28 AM, hisami dejima wrote:
Please someone tell me what they are?
About "inductive feedback and input capacitance"
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Yes, you can use feedback to cancel out the opposite value of reactance.
?
?
About "active notch"?
?
?
This is where feedback is used to create a resonant peak, but it is fed back in the opposite phase, to produce a notch in the frequency response ?
Regards,
?
Martin
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Re: "active antenna preamplifiers" in ham radio May 1986
Hi Vojtech,
?
Thanks for the reply.
?
"neutralisation" is a nostalgic word.
I hadn't been aware for years.
It filled few pieces of the puzzle.
?
Thanks also for the explanation of the traps.
?
I tried to improvise, but I burned 2N7002 and BS170.
even MOSFET is more clitical than I imagined.
fixed resistance is seems too rough for bias and VR is needed.
?
tnx & 73, Hisami 7L4IOU
?
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Re: "active antenna preamplifiers" in ham radio May 1986
On Wed, Mar 12, 2025 at 05:28 AM, hisami dejima wrote:
Hi All,
?
I found an interesting site, there a archive of the defunct "ham radio" magazine.
?
I have been reading this article intensively for the past few days.
"active antenna preamplifiers by R.W.Burhans, ham radio May 1986" pp.47-54
?
There are things I can't understand.
Please someone tell me what they are?
About "inductive feedback and input capacitance"
that says "A circuit that can reduce the input capacitance and improve the linearity for MOSFETs involves a noiseless feedback method" and "with the FET input capacitance reduced to pratical levels comparable to ..."
Does this mean that the inductance and capacitance cancel each other out?
Or does the NFB current or voltage physically reduce capacitance?
?
I try to explain it in few words. Yes, inductance and capacitance are canceling each out, this is the fact how the resonant circuits works. In old times, when the tubes have a lots of internal capacitance and feedback, the neutralisation was used and it was based on this principle too. How this work in active circuit is a bit complicated, you have to simulate the circuit and see what happens there. The negative feedback decreases the gain, but? can improve input impedance as well.
?
?
About "active notch"?
I have tried to the BC band notch between the Probe and the Amplifier or between the Small Loop and the Amplifier, but it does not work well.
It seems to be difficult with High-Z or Low-Z line.
Putting it in the ?NFB line looks like a good idea.
Have you tried it? Did you get good results?
?
The graph in the magazine answers clearly to that. Without the feedback, the reflective behavior of the BC bandstop is presenting high impedance on the input, which leads to the peak in gain and sometimes even to instability. The feedback can prevent such problems.
?
?
Actually, the MiniWhip I made at the end of last year looks exactly like fig.2 circuit and works well for VLF.
it running at?
?
and I hope to improve it.
I have no electrical or physics education (other than Ham radio), so please forgive my naive question.
?
73, Hisami 7L4IOU
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73s, OK1VAW, Vojtech.
?
?
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Added photo album Azi-Loop Self-Supporting Structure for Transportable / DXpedition Use
#photo-notice
Guy Atkins <dx@...> added the photo album
Azi-Loop Self-Supporting Structure for Transportable / DXpedition Use
: My in-progress design uses fiberglass rods to support and tension the lower legs of the triangular loops. Screw hooks along the length of each heat-shrink tubing covered rod allows quick removal of the loop wires (Teflon-covered 20AWG), along with weatherproof connectors that will be used near each pair of 90-deg. angle brackets.
I will upload more photos as the design progresses.
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Re: Reasonable size of an AziLoop?
Hi Christoph,
?
The image you uploaded from Dave's excellent presentation actually shows a circumference of 13.8m; close, but not quite the 15m you mentioned.
?
I currently have an Azi-Loop in the construction process; it's been taking some months due to other commitments. I am designing it to be easily transportable to take it from home to DXpedition sites, and also so that it will be mostly free-standing (fewer stakes and structures for the local deer to trip over or damage :^)? ?Like you I want the Azi-Loop to resist storms; I live on a hill above Aberdeen, WA USA, and we are vulnerable to Pacific coastal weather. The self-supporting "arms" for the lower horizontal loop segments are made from 3/8-inch dia. fiberglass rods (so-called driveway flags or markers). My hope is that the semi-flexibility of the rods will let the structure bend but not break in the winds.
?
As you've read, the Azi-Loop designer Dave recommends a modest 9.0m circumference. The dimensions of the Azi-Loop I'm building work out to a 10.56m circumference, so that's roughly similar to the size you are considering. Like you, my primary application will be the medium wave range.
?
Unfortunately I cannot give any comments just yet on performance, but hopefully in 2-3 weeks! I have a DXpedition to a beach location planned for mid-April, so I definitely need to have the antenna ready by then.
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You are probably familiar with the name of my Pacific Northwest DXing pal, Dr. Walt Salmaniw. He has an Azi-Loop among his antennas for MW DXing, at his Haida Gwaii, BC Canada vacation home. If you contact him I'm sure he'd be happy to give you comments on the antenna's performance. However, his antenna is built considerably larger than 10-15m circumference we are discussing. He decided to go larger since he has nearly zero chance of overload at that remote location.
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73,
Guy KE7MAV
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?
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"active antenna preamplifiers" in ham radio May 1986
Hi All,
?
I found an interesting site, there a archive of the defunct "ham radio" magazine.
?
I have been reading this article intensively for the past few days.
"active antenna preamplifiers by R.W.Burhans, ham radio May 1986" pp.47-54
?
There are things I can't understand.
Please someone tell me what they are?
About "inductive feedback and input capacitance"
that says "A circuit that can reduce the input capacitance and improve the linearity for MOSFETs involves a noiseless feedback method" and "with the FET input capacitance reduced to pratical levels comparable to ..."
Does this mean that the inductance and capacitance cancel each other out?
Or does the NFB current or voltage physically reduce capacitance?
?
About "active notch"?
I have tried to the BC band notch between the Probe and the Amplifier or between the Small Loop and the Amplifier, but it does not work well.
It seems to be difficult with High-Z or Low-Z line.
Putting it in the ?NFB line looks like a good idea.
Have you tried it? Did you get good results?
?
Actually, the MiniWhip I made at the end of last year looks exactly like fig.2 circuit and works well for VLF.
it running at?
?
and I hope to improve it.
I have no electrical or physics education (other than Ham radio), so please forgive my naive question.
?
73, Hisami 7L4IOU
?
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Reasonable size of an AziLoop?
Hello from Austria,
I am an enthusiastic mediumwave BC-DXer and operate a small remote station outside Salzburg, which I have built up over the last 14 years. ( As I don't own the land, I can't set up endless antennas there. At the moment I use a 200 metre two-wire Beverage and a K9AY (circumference of 30 meter), but it only listens to Asia and South America and is much too close to a house wall. The cows want it that way. But everything can be controlled remotely from QRO.cz, I'm very happy with it.
I'm thinking about setting up the ingenious AziLoop, which I could erect a good distance from the houses. The coax there is already buried, so far everything is fine. However, I have two problems at my location: the antenna has to survive storms well, and there are often storms there. And it has to be able to be dismantled quickly, but maybe I can talk my farmer out of that.
So I come to the point: I should - although the opposite would be better - erect the antenna as compactly as possible, also because I have to do everything myself. Dave specified a circumference of only 10 meters in his AziLoop manual (page 104). He wanted to cover this topic in more detail in the forthcoming manual, which will be much more comprehensive, but it has not yet been published. In an exciting (and humorous) talk at the Norfolk Amateur Radio Club, he presented the antenna and his thoughts: - starts at minute 20, the more technical part begins at minute 52.
In the presentation Dave showed a circumference of 15 meters, a picture is attached here. This size seems to me to be easily realisable, so my question is whether anyone here already has experience with a ‘relatively’ small AziLoop. My use is only intended from 500-1800 kHz. I have seen the perfect installation from Steve, VK5SFA, in the group - I don't know the exact size, but that seems ‘a size’ too big for me - even if I would do it exactly the same way. Then I would certainly hear AM stations from Australia better in Austria!
Thanks for your opinions.
73 Christoph, OE2CRM
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Re: TX protection on RX Loop
Addendum: I am more inclined to trust IN3OTD's data because there isn't much opportunity to screw up a S21 measurement on a VNA. However, the Cedola et al's time domain measurement (OCVD) has more potential to trip the unwary.
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Re: TX protection on RX Loop
On Thu, Feb 27, 2025 at 11:50 PM, Fred M wrote:
Sure, there are several measurements available in the web:
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The use of an 1N4007 as P.I.N. diode for Shortwave frequencies is well documented. See Jims link:
?
I have a problem reconciling the measurements of Cedola et al and IN3OTD.
I plotted IN3OTD's Fig. 1 data on a graph comparing 3 different types of real PIN diodes (below). ?IN3OTD's data are the red triangles in the graph. IN3OTD's data lies somewhere between the Tau = 0.5 uS diode (blue trace) and the 0.2 uS diode (red trace).
?
/g/loopantennas/photo/300438/3895061
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In contrast to the above, Cedola et al reported Tau = ~ 7 uS - clearly a very thick bulk diode. This discrepancy has implication on what is the suitable application for 1N4007: attenuator, switch or limiter?
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73, Leong, 9M2LCL, ex-9W2LC
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?
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#12-40 MOUNTING NUTS FOR MICA TRIMMER/PADDER CAPS
#12-40
If anyone needs mounting nuts for ARCO and other brands of "padder" or "trimmer"
capacitors, I have some that are surplus to my needs.? These are almost unobtainium....
VERY hard to find.?
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They are size 12 and have 40 threads-per-inch, solid brass.
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Charlie, N0TT?
n0tt at Juno.com
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Re: Why not a resonant loop?
This subject was extensively covered and commented on a few months ago.? I'd suggest you check the archives.
Personally, I don't want to tune the loop every time I chase something else.? They are extremely high-Q and tuning is required at BCB and HF frequencies for even a couple of 10 kHz.? No thanks.? My untuned loops work just fine!? I do have a single tuned 1-meter diameter loop I occasionally use for RCV and XMT on 40 and 20-meters during lightning season.? But on 40 the 2 : 1 bandwidth is roughly 6 kHz.? I don't use it too often.
Dave - W?LEV
On Sat, Mar 8, 2025 at 7:48?PM VLF Dilletante via <brownpiggin= [email protected]> wrote: I like tuned loop antennas for AM BCB as well as for NDB chasing. I have a 45 inch on a side box 8 turn loop wound with
#12 magnet wire and also use it as a crystal radio set. A good tuning capacitor is essential. I recently was given a Comet vacuum variable
8 to 1000pf capacitor and it is great for tuning the loop. Very sharp tuning and no need for a vernier. Better Q than my air variables for the BCB band as the tuning peak is sharper and the signal is stronger.
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?I am glad it was free. They are expensive capacitors!
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Re: Why not a resonant loop?
I have made several similar loops for BCB and NDB work. I wind the loop to about 330uH and use a BB112 Variactor to? resonate it, fed from a 0-10V Bias-Tee (indoors) . Very sharp / hi-Q and nothing expensive.
Here's the circuit, but with a different model loop using ferrite. Both the 1-meter loop and the rod loop work nicely with the BB112 circuitry.
Bob, N1KPR
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- Youtube: N1KPR
- Youtube: Ham Radio Doctor
Engineering, where enigma meets paradox
On Saturday, March 8, 2025 at 02:48:51 PM EST, VLF Dilletante via groups.io <brownpiggin@...> wrote:
I like tuned loop antennas for AM BCB as well as for NDB chasing. I have a 45 inch on a side box 8 turn loop wound with
#12 magnet wire and also use it as a crystal radio set. A good tuning capacitor is essential. I recently was given a Comet vacuum variable
8 to 1000pf capacitor and it is great for tuning the loop. Very sharp tuning and no need for a vernier. Better Q than my air variables for the BCB band as the tuning peak is sharper and the signal is stronger.
?
?I am glad it was free. They are expensive capacitors!
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Re: Why not a resonant loop?
I like tuned loop antennas for AM BCB as well as for NDB chasing. I have a 45 inch on a side box 8 turn loop wound with
#12 magnet wire and also use it as a crystal radio set. A good tuning capacitor is essential. I recently was given a Comet vacuum variable
8 to 1000pf capacitor and it is great for tuning the loop. Very sharp tuning and no need for a vernier. Better Q than my air variables for the BCB band as the tuning peak is sharper and the signal is stronger.
?
?I am glad it was free. They are expensive capacitors!
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If anyone is interested in a loop amp, or a phaser, please contact me off list. everettsharp (@) aol.com
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Everett N4CY
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Christoph Ratzer
Guy Atkins
Bob, N1KPR
Everett N4CY