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Even though the loop uses twisted pair network cable, and the amplifier & control boards have a decent amount of on-board filtering, it's still worthwhile adding yet more ferrite cored choke baluns on the cable. Multiple turns through a decent sized core, not just a few small clipon, single pass though types.

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Regards,

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Martin

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On Thu, May 15, 2025 at 06:34 AM, Fred M wrote:

Hi Fred,

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Thanks for the reply.

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The PSU is actually an iron core linear power supply - took me ages to find!

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I haven't tried switching modes. I don't have the switch built yet, I have just shorted the relevant pins to turn on A+B for both loops. Likewise, I might go and disconnect it and switch between loop and see what happens.

I am using a shielded cat6a for the FTP cable - however, only one end is connected to the shielded RJ45 (at the controller end)

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Ive already asked about the grounding point on the amplifier, and Martin has suggested I don't need to use this.

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I would imagine everything is all above ground currently.

Cheers

Sean

Looks perfect.

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The poor SND might be a problem of a noisy environment. The antenna actually receives, what's in the air.

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The AAA-1C allows switching between magnetic loop mode and electric dipole mode. Have you tried this und what is the result?
What about your power supply, is it a quiet linear regulated supply or a (noisy) switched supply?
Take care of possible noise ingress via unwanted ground loops.

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regards, Fred

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Never looked at my KiwiSDR2 SNR before. It is now 9..10dB,? local evening. I consider my QTH moderately bad. My current antenna is random L wire, 8m vertical + 12m angled to the ground.? There is a predistortion filter to reduce low HF by about 12dB, plus a strong 1.8MHz HPF and a strong 30MHz LPF (my interest is HF only).

I don't know how KiwiSDR measures the SNR. I see some remote Kiwis showing 10..12dB and they are not bad at all for my listening, while others are all noise while claiming the same SNR.

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73, Mike AF7KR

Hi Everyone,

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A little background, I have been into SWL for some time and recently got back into the hobby, and went down the slippery slope of SDR ;-)

I have a KiwiSDR2, and started with an MLA30+ which was OK. I tinkered with it, and broke it :-( and then decided to try an Apex Radio 303wa-2 which works great with a small LNA, however the local noise in my urban area is awful. So, after some deliberation and another hit on the credit card, I purchased a fresh off the production line, LZ1AQ AAA-1C. I was excited to see how it performed, because I can never seem to get much more than 10-20db of SNR, depending on the time of day. (on the Apex Antenna)

After some tinkering with what I already had around, and some more disappointing results had obtained some annealed copped pipe from a local HVAC workshop, who kindly gave me their off cuts, and its super easy to work with.




Initially I had a single loop with mixed results, and yesterday built this (I want to say monstrosity, however It's not really), an orthogonal loop. I didn't put a lot of science into the build, more feeling, however readying various notes on how these are built, suggests the most important thing is the material (like pure copper) and its area.

The loops are suspended on / in the PVC pipe and the shaft is metal which stops about where you see the first zip tie under the amplifier.

My issue is the performance. No more than 20db at silly o'clock (when I am sleeping) and SNR: 8 dB (0-30 MHz), 8 dB (1.8-30 MHz) right now, at 7.30am.

I've moved the antenna around the garden, however this seems to be the best place.

There is a lot to unpack here, however my first consideration is if I have configured the Amplifier correctly, as I found the instructions quite confusing.

Some more info.

I'm not using switches on the control board yet (that's to be made up) So I am shorting the relevant pins on the connector for now - which I confirmed working OK by checking the continuity of the A and B connectors. When shorted the relays open and when not shorted, the relays close.

The FTP cable is an outdoor rated Cat6 shielded. It's a PITA as it's thick, but it's all I had.

The PSU is an iron core 12VDC wall plug, which is delivering 14v no load, and the amplifier gets all of that from the control board.

Martin (G8JNJ) who is a guru of all things loop, suggest I should post in here :-)

Many thanks for looking and look forward to your feedback. (all and any welcome - as I'm still learning this craft)

Cheers

Sean (ZL2006SWL)

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Looking for a SAL-30? (no mast needed) .?

Nick VK9DX

vk9dx@...

Dear Whitham,

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Thank you for your kindness.
This wonderful device seems to me, to be of excessive quality.
and now I interested in the Hybrid itself and will continue to experiment.

Thank you very much again for your kindness.
73, Hisami 7L4IOU

Hello Hisami - I have two Anzac JH-6-4 couplers if you're interested.

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Contact me off-list at whitreeve@...

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Whitham D. Reeve
Anchorage, Alaska USA
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Hi Mark,

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Thank you very much.
I remembered a mistake I made in the past.
I wanted to use M-521CT as just a choke coil for BIAS-T.
I shorted the far end and input/output at the near end, but it did not work at all.
Now I know, I was trying to use leakage inductance.
Ignorance is a terrible thing!

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I will measure it later.

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73, Hisami 7L4IOU

Hi Hisami,

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On Thu, May 1, 2025 at 02:23 PM, hisami dejima wrote:

Is there an easy way to check the leakage inductance??

Yes.? For a transformer, you normally short the secondary and measure the inductance across the primary with an RLC bridge or a VNA.? You can also do this for a common mode choke. Alternatively, you can measure the inductance across the near end of the choke with the far end shorted.? Both methods should give about the same reading.? I just did this using a nanoVNA with nanoVNA-saver software for the Murata 50513AC.? I got 89nH.? ? The data sheet says it should be 70nH typical.

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Hi Hisami,

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The problem when using cores with greater permeability, is that the core loss tangent is likely to be greater, and the temperature stability may also be a problem, so you can easily trade one set of problems for another. I agree that self resonance could be an issue with so many turns, but the winding resistance shouldn't be.

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Type 61 mix ferrite would be my next suggestion, with a u' of 125, it may be an acceptable choice. 15 turns on an FT50-61 gets you in the ballpark for the desired value.

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Regards,

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Martin

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On Thu, May 1, 2025 at 09:08 PM, hisami dejima wrote:

Hi Mark,

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The construction of the M-521CT is a typical bifilar wound choke coil.

Is there an easy way to check the leakage inductance??

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tnx & 73, Hisami 7L4IOU

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Thank you for the advice.
There is certainly that concern.
but Iron Powder material requires a lot of turn, more resistance too.
I will try other cores and beads, paying attention to the self resonant frequency.

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tnx & 73, Hisami?

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You may find that the material used in the 33uH core you rewound for L3 is not best suited at RF frequencies. I have done similar in the past and found the results to be disappointing.

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Type 2 Iron powder is just about a high enough value of permeability. Approx 50 turns on a T50-2 core should get you started.

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Regards,

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Martin

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On Tue, Apr 29, 2025 at 11:10 PM, hisami dejima wrote:

Hi Hisami,

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Unfortunately, the M-521CT data sheet does not have a leakage inductance spec or a differential impedance plot.? I will order a couple next week, put them in my circuit and see how they perform.

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