Re: Steve ugly-build LZ1AQ using MPS2222 sweeps uploaded to Photos
Hi Martin,
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Well when you have a separate 50 ohms coupling loop ( your excitation loop ) coupled with a tuned loop:?
1. More separation betveen both loops - lower the magnetic coupling K coefficient, less induced power from excitation loop into the tuned loop.
2. Less separation, the coupling coefficient rises, induced power goes up and the resonant frequency of tuned loop goes up insignificantly in accordance with:? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? f= 1/2xpi x sqrt (( La (1-K^2)x Ca)) .
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Raphael
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Re: Wellbrook traced-out loop amp schematics uploaded to Photos
Steve,
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Thanks for doing this. It would be a shame to lose these designs now that Andy is gone.
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I added a folder and two files illustrating T1:
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Could you take a look and see if I have it correct?
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Thanks!
--
===================================================================
Mike M
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Re: I've posted JFET Evaluation for active antennas Trask
I'd like to see that Russian verswion. Could you forward it?
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Chris
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When the going gets weird, the weird turn pro
- Hunter S. Thompson
-----Original Message----- From: < [email protected]> Sent: Jul 20, 2024 8:44 AM To: < [email protected]> Subject: Re: [loopantennas] I've posted JFET Evaluation for active antennas Trask
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I found this in my saved documents on my PC. The weblinks on the net no longer work, but I did find a? MS Word version in Russian.
Regards, Ian.
On 20/07/2024 16:34, wn4isx via groups.io wrote:
I've posted JFET Evaluation for active antennas Trask in the files section.
A very nice paper on various JFET response.?
While the paper is for E-Field antennas, the data is valid for any JFET application.
?
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Re: Wellbrook antenna troubleshooting help
First, disconnect the anttena, Is the red light on?? My antenna interface is like yours, has a resettable fuse too.
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Ckeck your power supply, and check the interface output with a voltmeter
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Re: LZ1AQ Purchase Control Board Only
I will repeat Chavdar's commercial email address (he produces the amplifier and interface board under the active-antenna.eu brand name) as before.
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Use the for or following address:
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info(AT)active-antenna.eu?? Replace the (AT) with @ as Groups IO strips full email addresses for security purposes.
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On Sat, Jul 20, 2024 at 06:27 PM, KQ4NUO wrote:
There is no email address on the site for Chavdar
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Re: Wellbrook antenna troubleshooting help
Hi Todd,
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Measure the DC current being drawn by the loop amplifier, somewhere along the coax feeding the loop.
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This will determine that power is actually reaching the amplifier, and if the devices are OK.
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The current will ?most likely be in the region of 100 to 150mA if it is working correctly.
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It is possible the previous owner has accidentally transmitted into to loop interface and caused damage. This has happened to the majority of faulty ones I have been asked to look at.
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Regards,
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Martin
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Wellbrook antenna troubleshooting help
Hello all,
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I am trying to troubleshoot an issue with a used Wellbrook antenna.? When I set it up the day before yesterday, it was working very well!? Then today I noticed a problem with an intermittent LED on the antenna interface not lighting up (as if no power was getting to the unit).? I found some troubleshooting steps on this forum and checked the following and found to be good:
1.? co-ax is ok (using new RG58)
2. Power is at 12 V to the unit
3. Red LED is now lit up.
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However, now there appears to be absolutely no signals being picked up, it's completely deaf.? Is there something else to check?? The only other thing I can think of is checking the connections to the loop at the amplifier (they are tightly taped by the previous owner, so I suspect they would be good).
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Thanks,
Todd
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Some additional power supply notes.
Some additional power supply notes.
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I mentioned there is a severe problem in the way most circuit designs for the uA723 have an error. I said I thought 100 ohms was needed in series with the current sense, it is 1,000 ohms. Most fried uA723 are the result of not using that 1,000 ohm resistor.
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Re noise from batteries.
Mr. Werner Ogiers is a severe audiophile. While I don't necessarily agree with severe audiophiles, I mean oxygen free cryogenically treated copper speaker cables strikes me as a bit unsane, there are some very smart and dedicated people in that clan who actually understand measurement.
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Mr. Ogiers has a series on power supplies and page 4 has noise graphs from chemical batteries.
I doubted his data and performed some tests of my own. [forget the "Some people prefer the sound of the TL431 operating in non-unity-gain" on page 3, even very smart people have their delusions.]
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I used Rod Elliot's Low Noise Test Preamplifier
at https://sound-au.com/project158.htm
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My Dataq data acquisition unit with the Low Noise Test preamplifier with SpectraPluse revealed that "Yyes chemical batteries do produce noise."
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Some batteries produce a lot of noise. And I mean A LOT of NOISE!
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https://www.tnt-audio.com/clinica/regulators_noise4_e.html
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Take it for what it's worth.
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I use Charles Wenzel's Reducing Voltage Regulator Noise
for all of my active antenna power supplies.
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For really critical, low current, needs I add a capacitor multiplier to the output. The noise is so low I can't measure it.
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Something all too many RF designers ignore is "rectifier commutation noise."
https://www.microsemi.com/document-portal/doc_view/14617-rectifier-reverse-switching-performance
[rectifier commutation noise is the term my favorite EE professor used.]
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I won't get down into the weeds over proper rectifier commutation noise snubber design but this can be a serious problem. By serious, I mean so bad as to render a very well designed linear power supply useless for RF work.
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One final note, there is no point in lowering your home grown EMI lower then the ambient RF noise floor, which, if you have AC power, telephone, cable TV, and neighbors within ~300 feet, will be rather high. Such is life and why my wife and I try to escape to a nature preserve so I can do some serious DXing.
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Re: LZ1AQ Purchase Control Board Only
There is no email address on the site for Chavdar ?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]] On Behalf Of Martin - Southwest UK via groups.io
Sent: Saturday, July 20, 2024 1:58 PM
To: [email protected]
Subject: Re: [loopantennas] LZ1AQ Purchase Control Board Only ? Send an email to Chavdar. For additional info please use the for or following address: info(AT)active-antenna.eu On Sat, Jul 20, 2024 at 04:21 PM, KQ4NUO wrote: We misplaced the small Control Board for our LZ1AQ. Does anyone know how to purchase it only without the whole kit or how to contact the manufacturer to buy replacement?
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Re: LZ1AQ Purchase Control Board Only
Send an email to Chavdar.
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For additional info please use the for or following address:
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info(AT)active-antenna.eu
?
?
?
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On Sat, Jul 20, 2024 at 04:21 PM, KQ4NUO wrote:
We misplaced the small Control Board for our LZ1AQ. Does anyone know how to purchase it only without the whole kit or how to contact the manufacturer to buy replacement?
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Re: I've posted JFET Evaluation for active antennas Trask
As I told Steve, someday soon I hope to collect all the Trask papers I've got stashed on several hard drives into one subdirectory. I believe Mr. Trask has several papers on loop antennas.?
"Someday soon" should be understood to mean sometime before the sun runs out of hydrogen.
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LZ1AQ Purchase Control Board Only
We misplaced the small Control Board for our LZ1AQ. Does anyone know how to purchase it only without the whole kit or how to contact the manufacturer to buy replacement?
Thanks
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Re: LF noise measurements
I recently discovered the TI JFE2140 dual JFET:
0.9 nV/sqrtHz noise and 100 Hz 3dB 1/f dB corner
There is an excellent ap note:
TI even has evaluation boards for it.
What I like about it is that this is in current production by
a major semiconductor manufacturer using a current process.
Should be very repeatable.
Is anyone reading this list using it? It seems to be just about
as good as the discontinued BF862 that MVaudiolabs raves about.
Rick N6RK
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Re: I've posted JFET Evaluation for active antennas Trask
I found this in my saved documents on my PC. The weblinks on the
net no longer work, but I did find a? MS Word version in Russian.
Regards, Ian.
On 20/07/2024 16:34, wn4isx via
groups.io wrote:
toggle quoted message
Show quoted text
I've posted JFET Evaluation for active antennas Trask in the
files section.
A very nice paper on various JFET response.?
While the paper is for E-Field antennas, the data is valid
for any JFET application.
|
I've posted JFET Evaluation for active antennas Trask
I've posted JFET Evaluation for active antennas Trask in the files section.
A very nice paper on various JFET response.?
While the paper is for E-Field antennas, the data is valid for any JFET application.
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Re: Found the paper by Trask that reviews JEFTs
Chris
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When the going gets weird, the weird turn pro
- Hunter S. Thompson
-----Original Message----- From: < [email protected]> Sent: Jul 19, 2024 2:39 PM To: < [email protected]> Subject: [loopantennas] Found the paper by Trask that reviews JEFTs
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This might, or might not, be of interest to group member, and might, or might not, be appropriate to place in the files section.
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I did a search in my randomly organized archive and found Chris Trask's "An Evaluation of Junction Field-Effect Transistors Suitable for Active Antenna Applications."
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This paper shows the curves of various JFETs and might be useful.
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The paper is from 2008, so it is a bit dated and it is for E-Field antennas and not loop antennas.
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If there is interest, and a group consensus it is appropriate, I'll drop it there tomorrow or Sunday with a better description of the file.
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Mr. Trask are you still a member and would you approve?
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Re: LF noise measurements
Another trick you can use is to parallel many JFETs to give lower noise. You add the outputs of each JFET. That way the noise adds as an RMS value, since it is random, but the signal adds arithmetically. So if you have two JFETs you get twice the signal but only 1.4 times the noise.
Paralleling multiple devices to lower noise is not unique to audio. There are similar prior arts at RF & microwave too (see below).
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Amplifier for FM antennas - Patent 6653905
https://patents.google.com/patent/US20030146793
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Very Low Noise Amplifiers at 300K for 0.7 to 1.4 GHz
http://astro.uchicago.edu/ursi-comm-J/ursi2005/
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You can also consider a FET with a very wide gate as similar to connecting multiple devices in parallel. To give some numbers to this concept: . ?
73, Chin-Leong Lim, 9W2LC
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Re: Steve ugly-build LZ1AQ using MPS2222 sweeps uploaded to Photos
I linked the Duffy article in post#19752. The section at the end of that article is sub-titled " Diodes connected to antennas" 73, Chin-Leong Lim, 9W2LC
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Re: Urban HF Antenna Dilemma: LZ1AQ vs. M0AYF
The transformer is 4:1 turns ratio.... 16:1 impedance ratio.
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Re: Urban HF Antenna Dilemma: LZ1AQ vs. M0AYF
Update:
Added Chebyshev 3-8 MHz 3rd Order BPF, and also replaced the 1uF input caps by 100nF ones as they resulted in a flatter response between 3-4MHz and improved MF rejection.
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Also performed some tests with a small input transformer (4:1) connected to an "ugly loop" made from a 4m segment of RG11 coax.
Reception was crappy, as The loop was resting partially on the floor and close to AC wiring, but it was enough to confirm that the signal pickup increased some 10 dB with that transformer.
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I have to try a better loop on the roof, far from my lab, power supplies, etc.
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One thing I noticed is how strong the signal level from the LZ1AQ preamp is. I had to turn the attenuator on, as the noise floor of the preamp alone was aronund S5 and rised to S9 with the loop connected.
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Ian Brooks
Caaarlo