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Re: "active antenna preamplifiers" in ham radio May 1986
Although the basic concepts and principles are sound, things have moved on over the 40+ years that have passed since the articles were published.
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Regards,
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Martin
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On Fri, Mar 14, 2025 at 07:30 PM, crabtreejr wrote:
Ralph Burhans wrote an excellent series of antenna articles in Radio Electronics in 1983: |
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Re: "active antenna preamplifiers" in ham radio May 1986
Ralph Burhans wrote an excellent series of antenna articles in Radio Electronics in 1983: ? ?February 1983, part 1 - All about VLF Active Antennas ? ?March 1983, part 2 - All about VLF Active Antennas,?plus corrections, August 1983, p. 25 ? ?April 1983, part 3 - VLF-HF Active Antennas ? ?May 1983, part 4 -?VLF-HF Passive Antenna Tuner ? ?June 1983, part 5 - Low Frequency Loop Antennas In addition he contributed these articles to Radio Electronics in 1983: ? ?July 1983 - Using Loran for Time and Frequency Calibration ? ?September 1983 - Frequency Calibration using WWV ? ?December 1983 - Interference Traps for SWL's At Fig. 7 of his 1986 article in Ham Radio Magazine, Burhans showed an VLF-LF utility amplifier using a noiseless feedback input.? Ulrich Rohde had shown these techniques in his article in the November 1979 issue of Ham Radio Magazine. The AMRAD active antenna referenced by Steve Ratzlaff below used a CP666 FET from Crystalonics Inc..? They seem to have closed or moved in the last few months.? Unfortunately their web site ? ?? is no longer working.? Their telephone number is no longer in service.?? 73? John? KC0G/M0KCY
On Wednesday, March 12, 2025 at 10:34:35 PM CDT, Steve Ratzlaff via groups.io <ratzlaffsteve@...> wrote:
The AMRAD active antenna is based on Burhan's circuit.?? W1VD also has a version using a common J310 jfet.?? 73, Steve AA7U On 3/11/2025 9:28 PM, hisami dejima via
groups.io wrote:
Hi All,
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I found an interesting site, there a archive of the defunct
"ham radio" magazine.
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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
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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.
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73, Hisami 7L4IOU
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Re: Aziloop
Well, the truth be known, I mostly use the 0.5-meter "shielded" loop for DF'ing RFI.? It's great for that.? But, yes, the null is bidirectional. Dave - W?LEV On Fri, Mar 14, 2025 at 6:48?PM Simon via <ohhellnotagain=[email protected]> wrote: Hi Dave.. totally agree..when comes to antennas I hate to buy!! --
Dave - W?LEV |
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Re: Aziloop
Hi Dave.. totally agree..when comes to antennas I hate to buy!!
However, not all feel the need to do so, or have the time to do. (Dave you are on rsgb technical, you have no doubt seen my thread on short marconi T for 160m and the quest to improve, so on same page. (Getting better btw, vk’s on ft8 now.)) The “ standard loop” has short falls .. bi directional being one..(hence the k9ay/ azi- loop.) Ie yes ( standard loop) stunning null, but not much use if ( example) dx is north and qrm ( from local station) is south. Simon g0zen |
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Re: Aziloop
Understand, Simon.? In retirement, US $$$$ are not an option for me.? That's why, whenever possible, I build my own. Dave - W?LEV On Fri, Mar 14, 2025 at 6:11?PM Simon via <ohhellnotagain=[email protected]> wrote: Hi Bill --
Dave - W?LEV |
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Re: Aziloop
Hi Bill
( and Dave) Bill has paid a good few bucks for the Azi-loop if its from UK, so wants it to work as advertised.( if not a knock off.) It should av a better f/b than that. But Bill remember its just a flash k9ay loop.. Size of loop matters, placement etc.. Bill, if it’s the UK version get in contact with the maker and ask for advice? I just hear good things about them, though it wont be better than a k9ay ( of same size) on a rotator with variable R over a reasonable gnd. Keep us informed..Simon g0zen |
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Re: Aziloop
If you are searching for nulls, I find a "shielded" 0.5-meter loop made of 0.5-inch copper tubing hard to beat.? Five internal turns, the center of which is cut and brought out to a home brew and characterized (using an HP VNA) broadband transformer.?? We have a "blowtorch" AM transmitter in Boulder, Colorado on 760 kHz which measures -24 dBm on any of my outdoor dipoles (not cut to frequency - they're all quite short for the frequency).? I'm only some 25 or so miles from the transmitter on the Front Range of the Rockies.? The null with that small loop is so sharp and deep that I'm able to null out that "blowtorch" during day or night (no reduction in power after sunset) to receive other distant stations.? I haven't measured the null depth, but it must be in excess of 40 to 50 dB. Dave - W?LEV? On Fri, Mar 14, 2025 at 5:10?PM Bill Riches via <bill.riches=[email protected]> wrote:
--
Dave - W?LEV |
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Re: "active antenna preamplifiers" in ham radio May 1986
On Thu, Mar 13, 2025 at 08:54 AM, Martin - Southwest UK wrote:
The better IMD performance of the Trask circuit, means that it can be used with a larger antenna (one having greater self capacitance) such as a 1m whip. ?Hi Martin, Thank you very much for the explanation, it all makes sense. Yes I was thinking flat plate antenna.
???????????????????????????????????????????????????????????????????????? Mikek |
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Re: "active antenna preamplifiers" in ham radio May 1986
A tour de force by Chris Trask!! Re my previous suggestion of using constant current sources replacing R1 and R2 in Everett's great circuit, I leave the following quote by Chris.... >> The first of these circuits is shown in Fig.4. Here, the source load inductor of the KAA 1000 has been replaced with a JFET constant current source (Q2), where resistor R3 determines the bias current for the JFET source for Fig. 5 - Complementary Push-Pull Amplifier with Complementary Push-Pull Input Stage lower (Q1). This active load provides a very high load impedance for the Q1 source follower, which in turn results in better IMD performance of the input stage.<< best wishes Paul VE3PVB Collingwood ON CANADA
On Friday, March 14, 2025 at 06:30:10 a.m. EDT, Martin - Southwest UK via groups.io <martin_ehrenfried@...> wrote:
Hi Hisami,
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This is the paper the design was taken from.
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Regards,
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Martin
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On Thu, Mar 13, 2025 at 11:27 PM, hisami dejima wrote:
Thanks also for the recommend on "Chris Trask (fig.5)". |
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Re: "active antenna preamplifiers" in ham radio May 1986
Hi Hisami,
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This is the paper the design was taken from.
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Regards,
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Martin
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On Thu, Mar 13, 2025 at 11:27 PM, hisami dejima wrote:
Thanks also for the recommend on "Chris Trask (fig.5)". |
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Aziloop
I have just installed an Aziloop and I do not get good nulls - 10 -15 dB on 50 -100-mile ground wave signals, Loop is 13' on long side, 8' on short side and PVC mast is 15 feet. Radials are on the ground below the loop elements. It is fed with about 200' of RG6 cable and the?supply voltage is 12.7 volts. I have a SAL-20 antenna 40 feet north of the AZI.? I can get 15-30 dB nulls with it.? I have a 60 foot self-supported welded steel tower with a large 10–40-meter Mosley beam at the top 42' east of the Azi. Antennas are in the middle of a 1.5 acre lot - no other buildings or metal nearby.? Ground elevation is 15 feet ASL. Could these two other antennas be affecting the poor null operation on the Azi??? Any suggestions would be appreciated. 73, Bill, WA2DVU Cape May, NJ 609 425 8651 |
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Re: "active antenna preamplifiers" in ham radio May 1986
Hi ?Mikek,
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The better IMD performance of the Trask circuit, means that it can be used with a larger antenna (one having greater self capacitance) such as a 1m whip.
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The coax transmission line forms a major part of the antenna anyway, so I see little point in having an excessively high value of input impedance, just so that a very small "plate" can be used.
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By using an antenna with a larger value of self capacitance, the issue of the amplifier input shunt capacitance, that otherwise degrades the Signal to Noise performance, is minimised.
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If you use a small plate with a self capacitance value of say 0.5pF, and the amplifier input capacitance is say 2pF (including mounting), then the majority of the input signal is shunted to ground. A 1m whip has a value of self capacitance of around 10 - 15pF, so the amplifier shunt capacitance is much less of an issue.
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Using a larger antenna, also reduces the need for an excessively high value of amplifier input resistance, which also helps reduce problems associated with choking common mode noise induced in the feed line.
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Regards,
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Martin
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On Thu, Mar 13, 2025 at 03:42 PM, Mikek wrote:
I have a question about the Trask push-pull amplifier. Doesn't it have a rather low input impedance to be connected to a probe antenna? |
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Re: "active antenna preamplifiers" in ham radio May 1986
Hi Hisami,
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The PA0RDT ?
PA3FWM
PA0NHC dual fet
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Are probably the best simple designs around at the moment.
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My favourite remains the Chris Trask (fig.5) which I believe offers the bast trade between performance, cost and ease of construction.
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My previous active antenna experiments can be found at
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Regards,
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Martin
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On Wed, Mar 12, 2025 at 11:34 PM, hisami dejima wrote:
Thanks for the advice. |
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Re: "active antenna preamplifiers" in ham radio May 1986
开云体育The AMRAD active antenna is based on Burhan's circuit.?? W1VD also has a version using a common J310 jfet.?? 73, Steve AA7U On 3/11/2025 9:28 PM, hisami dejima via
groups.io wrote:
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Bill Riches
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