Re: TX protection on RX Loop
Are we maybe overthinking this ?
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A pair of back to back 1N4148's or a BAV99 should be perfectly adequate in a receive situation.
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I use a pair of 1N4148's across the antenna cable from my "old school" external car radio antenna, that feeds the broadcast radio, as I also use a roof mounted screwdriver HF transmit antenna that is less than a metre away, and I've not had any problems from the 100w of RF that is being radiated.
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Regards,
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Martin
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Re: TX protection on RX Loop
Hi Andrew,
The 1N4148 ist a fast switching Diode. Some 1N4007 have a long carrier lifetime and behave like a HF PIN Diode.
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regards, Fred
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Re: TX protection on RX Loop
Hi Jim,
I wonder if a 1n4148 and a 1n4007 would work in the same way for HF?
Andrew VK5CV
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From: loopantennas@groups.io <loopantennas@groups.io> on behalf of Adam via groups.io <adamtoynton@...>
Sent: Thursday, 27 February 2025 6:14:22 pm
To: loopantennas@groups.io <loopantennas@groups.io>
Subject: Re: [loopantennas] TX protection on RX Loop
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Jim, thank you. It's always easier to follow a diagram. Much appreciated
Adam
On Thu, 27 Feb 2025 at 3:13, James Redding WA9VEZ via groups.io
<wa9vez@...> wrote:
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It will be informative to follow the link below:
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Have a nice day!
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Jim/VEZ
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Re: TX protection on RX Loop
Jim, thank you. It's always easier to follow a diagram. Much appreciated
On Thu, 27 Feb 2025 at 3:13, James Redding WA9VEZ via groups.io <wa9vez@...> wrote: ?
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It will be informative to follow the link below:
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Have a nice day!
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Jim/VEZ
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Re: TX protection on RX Loop
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It will be informative to follow the link below:
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Have a nice day!
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Jim/VEZ
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Re: File upload: Rotable FLAG-antenna
Hi Fred,
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If I recall, it was an experiment I tried after reading about *tuned* spiral loops (windings in the same plane) in the early days of radio. My intented use was MW only, and I was seeking a greater amount of wire in the same space, and hoped this would work for a broadband loop also, vs. tuned. Indeed, it never worked as well as my single turn version, although it still had some good nulling ability on MW.
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Guy
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Re: File upload: Rotable FLAG-antenna
Hi Guy,
why did you choose a spiral-loop?
The enclosed loop area is a key figure of merit of a small magnetic broadband loop. With a spiral loop the enclosed loop area decreases with each winding.
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regards
Fred
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On Sun, Feb 23, 2025 at 10:01 PM, James Redding WA9VEZ wrote:
Sort of a shame the WW2 400 Hz selsyns are no longer "inexpensive" although a PM magnet, an Arduino flux compass, and some hot glue will probably replace a selsyn and all the analog hardware to remotely read out azimuth position in degrees.
I've agonised over azimuth sensing - been looking for a battery-powered device with built-in Wi-Fi or Bluetooth sender and a PC Windows receiver that "exposes" the azimuth value for easy capture by a simple program (e.g. data logger).
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Some years ago I tried a device from (via Amazon) with a display program that tries to mimic an aircraft attitude indicator. It was disorientating and made me tear my hair out. And anyway this did not let me capture the azimuth value.
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I have that exact rotator. It is fine for a 1 to 1.5m diameter loop. Although the readout only indicates 10 degree steps, it can be "jogged" to any position allowing good nulls if necessary. Tom
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There is a re-calibration sequence in the manual if it get out of whack, but I'm not sure if it covers that situation.
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Re: File upload: Rotable FLAG-antenna
Oops, this 3rd link is the one for photos of the spiral loop on rotor:
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-Guy
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Re: File upload: Rotable FLAG-antenna
I did something similar in 2008. One design was a small bidirectional loop on a rotor, and the other was a four-turn spiral loop on a rotor. Both used Wellbrook ALA100 modules. Support elements in one case was fiberglass fishing poles, and fiberglass tent poles for the other:
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73,
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Guy
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Re: File upload: Rotable FLAG-antenna
The shape isn't critical. Att that matters is loop area (length x height). Bigger area, more gain.
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/Hans
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Re: File upload: Rotable FLAG-antenna
The SULA is a smaller loop than most FLAG antennas but both bigger than a YouLoop
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Regardless they are interesting to experiment with and can use a preamplifier
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The County Wireless loop amp is a great one to use, low noise floor
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John VE3IPS?
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I have the predecessor unit and it is just a two winding capacitor (direction) induction motor with a gear train. The digital display seems to be counting AC cycles. A strong wind (or in my case power mains failure) can push a 12' yagi out of alignment. In short it is not like a CDR type with an internal wire wound resistor measuring direction.
Sort of a shame the WW2 400 Hz selsyns are no longer "inexpensive" although a PM magnet, an Arduino flux compass, and some hot glue will probably replace a selsyn and all the analog hardware to remotely read out azimuth position in degrees.
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Re: File upload: Rotable FLAG-antenna
What about this diamond shape antenna, would it better? I have a Wellbrook FLG100 Wellbrok module amplifier. I dont know if the growning flag will be better.
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https://swling.com/blog/tag/small-unidirectional-loop-antenna-sula/
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https://swling.net/viewtopic.php?t=55
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I just saw this RCA rotor on sale, I don't know that is is precise enough, because it is programmable for every 10 degrees. I haven't read the manual
far enough to see if you can precisely set direction to null your noise sources or if you can fool it to ever 5degrees by only turning 180 degrees.
It is $89 on sale with rebate.? $14 shipping, at least to me in Fl.
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Here's the manual,
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???????????????? Mikek
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Re: Entry Level SDR recommendations
Maybe is the power supply causing this problem. I have tried to feed with a well filtered external USB adptor but the problem persit. I forgot also I purchased a USB isolator but not results at all . I have several 31-43 mix toroids and big 43 ferrite clamps.? As I said before the cable is not too long I will purchase extra cables in order to wind the toroids.
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Re: Entry Level SDR recommendations
I agree with Simon, and he raises a valid point that you can use smaller diameter cables, but sometimes things like moulded USB connectors prevent their use, and you have to resort to larger cores.
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Regards,
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Martin
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On Sun, Feb 23, 2025 at 06:47 PM, Simon wrote:
However you do NOT need to use ft240/(31/43) cores.. Ft240 is the size of core. As your cable is not rg213 ie thick, one can use cheaper smaller diameter cores..just as long as one can get the required turns though and are of same spec. Ie type 31/43 etc.
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Re: Entry Level SDR recommendations
If the amplifier is genuinely running in class A (which I doubt) it should not generate any RFI.
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It is difficult to tell from the video if the interference varies in unison with the audio, but the Spectrum Analyser plots suggest a single switching frequency and harmonics, which to me suggests a power supply issue.
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I believe the noise is most likely being introduced from the USB port, or whatever is powering the amplifier, so personally I would concentrate on that rather than the amplifier, as I think you have tried just about every usual technique of RFI suppression on the PCB itself.
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I'd suggest trying a screened PSU cable, with good decoupling of the supply cores at each end, and a decent bond to ground at the PC end.
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Regards,
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Martin
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On Sun, Feb 23, 2025 at 05:17 PM, enriqueeeeee2001 wrote:
Trust speakers, it has a class A amplifier and radiates a lot s of RFI
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Adam
James Redding WA9VEZ
Guy Atkins
Hans Ostnell
John