Transmit audio distorted when connected to Antenna, audio is fine when in dummy load.

[Tech Minds]

Hi all,

I have the most bizarre issue with a brand new HL2 with N2ADR filter board.

Power source: 13.8v 50amp shack PSU

Transmit software: SDR Console

Receive software: SDRConnect with RSPdx / 1b

Connection: Ethernet

Antenna EFHW Multi-Band

Dummy load 100 Watt 50Ohm dummy load.

The issue is that when transmitting with an antenna connected my audio is distorted. It is even more apparent when transmitting on FM. There is almost like a main hum.

When using the same setup, but transmitting into a dummy load, the audio distortion on SSB and noticeable on FM, is gone!

Fearing it was the PSU, I powered the HL2 from a Bionno battery, and the issue is exactly the same. Still get the buzz when transmitting into an antenna even from a battery.

Please see the following video:

https://www.youtube.com/watch?v=60zuSxvzP9I

Please note I have had many HL2 and this is the first time I have seen this issue.

Any suggestions welcomed.

Thanks!

Matt

M0DQW

YT: TechMinds

[Brock Nanson]

That sounds like it could be RF getting into your audio somewhere.  Perhaps try a common mode choke on your feedline?  Or add a ferrite to your mic cable?

Brock VA7AV

[ron.ni...@gmail.com]

The first thing I would suspect, when there is a difference in behavior between transmitting into a dummy load and transmitting into an unbalanced antenna, such as an EFHW, is common mode RF on the antenna feedline coupling into the SDR computer cables (microphone, other audio, keyboard, mouse, other USB, power, and etc.)  A commonly suggested solution is to choke the feedline and/or the computer cables with multiple turns through ferrite toroids of a suitable mix.

73, Ron, n6ywu

On Tuesday, June 4, 2024 at 9:30:32 AM UTC-7 Tech Minds wrote:

[Tech Minds]

I would agree with you, but not with the power slider on SDR Console set to the minimum it can go. I use the same antenna on other radios and don'f get this issue.

This is 100% an issue with either the filter board or the main HL2 board... Just need some pointers where to check before I request a return.

Thanks

Matt

[Tech Minds]

And I already have 1:1 chokes inline. I solved that issue long ago when I first started with EFHW lol :-)

[Steve Haynal]

Hi Matt,

Just to confirm, if you swap our just your HL2, the problem goes away, so the HL2 is the only variable? And you tried that recently?

Do you see the distortion with a key down CW transmission? Do you see the distortion at all drive levels, when adjusting just the hardware 7.5dB gain for TX?

One possible cause could be the oscillator or clock generator in this HL2 is sensitive to RF. That might explain why the problem is more apparent with FM. Can you try applying some finger pressure to X2 and U6 (top side of PCB, in the area near the CW/PTT jack) and see if that changes the behavior?

73,

Steve

kf7o

[ron.ni...@gmail.com]

Is the problem some sort of buzz sound?  Have you listened to the HL2 enclosure to make sure it's not the HL2's relays that are clicking?

73, Ron, n6ywu

[Neil Howard]

Matt,

 I have seen a similar problem, and it had my head scratching - I didn't hear a buzz on FM though.. The problem turned out to be the the actual negative lead from the power supply to the HL2 was broken, and the power only earth was through the antenna!! So maybe look for some weird earthing path... 

Good luck!

Neil  M0KNC

[Tech Minds]

Hi Steve (and everyone else)

To answer your questions:

1) Yes, it;s just this new HL2 which has the problem. I am actively working trying to fix the issue as I want this one to be my main HF station.

2) Yes, I also see the issue with a key down on CW using the front ptt port. Its like a buzzing sound mixed in.

3) Yes, all drive levels I see the distortion

4) I have tried applying pressure to the X2 and U6 area with no effect on transmission

5) No relays are chattering

Here is another video demonstrating the transmitted audio on ssb:

https://www.youtube.com/watch?v=rrPtUT4MG0M

I have even setup another sdr receiver, well away from the shack, and the results are the same.

I find it very strange that this does not happen when I attach a dummy load. There should be no difference, and by all accounts this would indicate an RF in the audio chain problem, but its cant be, not at the minimum drive level.

Any thoughts @Steve? Or are we looking to send this back for a replacement? The problem is here, is whether its the filter board or the main HL2 board?

Thanks so much!

Matt

M0DQW

[Ed Grafton]

I dont know if anyone mentioned to try ferrites on your USB &  power cables for the HL2.

Ed

[Tech Minds]

Thanks for the suggestion Ed but the issue is not related to rf getting into any usb and power cables. I have tried running from batteries and from another computer (via ethernet) and still the same issue.

@Steve Haynal  What is the RMA procedure with makerfabs please? And do I return both the filter board and the HL2?

Thanks

Matt

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[Steve Haynal]

Hi Matt,

Since you have multiple HL2, can you try swapping out the N2ADR board with another one you have? We can at least check if the problem is with that board.

Do you see this same problem across multiple bands?

One cause for TX distortion I've seen in the past is if one of the DAC lines were open or shorted with another. But you would observe this with a dummy load. When you use the dummy load, are you reducing the amplitude of your audio test signal versus without the dummy load? If so, that could not utilize all the bits to the DAC and thus not distort.

Another explanation is that RF is getting into the HL2 and affecting some component which is more sensitive (or even the wrong value) versus your other HL2s. For example, if the analog power supply to the AD9866 was not filtering out noise as much on this unit it might explain the distortion. Do you have a scope and desire to check for noise on various power supplies? I can also point you to some specific AD9866 analog power supply test points.

The explanation of a missing ground connection is possible, but I think your battery test wouldn't have worked then.

You can post high resolution top/bottom photos of your boards and we can take a look.

The Makerfabs "warranty and return" link is at the bottom of their main page. More details are on the repair wiki page.

73,

Steve

kf7o

[Steve Haynal]

The power output is a little higher on the newers HL2s. Are you certain your receiver is not being overloaded?

[Tech Minds]

Hi Steve,

Thanks for the pointers.

1) My other HL2 boards are not accessible for the foreseeable future, otherwise I would of done a test with the other boards.

2) Not a ground issue as I have tried multiple leads, power supplies and batteries (Bioneno)

3) Don't have a scope :-(

4) Checked voltages as per the link you shared and they match

5) I setup a KiwiSDR with a small telescopic antenna downstairs (as my shack is upstairs). Even with the lowest power setting on Thetis or SDR Console the buzz/noise is apparent.

6) I also tried using a laptop connect to the local network here, running off battery, and still the same buzz/noise on transmission.

Attached are some photos, if you need a close up of certain parts let me know, I have a camera microscope I can set up.

Many thanks for your support, its most appreciated!

Regards,

Matt

[ron.ni...@gmail.com]

Are you connecting to the HL2 with an ethernet cable directly between your computer and the HL2, or through a router or switch?  If through a router or switch, could RF be getting into one of those?  Also, what's the SWR reported for your EFHW antenna?  73, Ron, n6ywu

[Tech Minds]

@ron.ni...@gmail.com Through a switch in my home. Antenna swapped to a remote tuned wire, so close to 1:1. Doubt it would be rf getting into the cables as this happens with the power level set to minimum too.

@Steve Haynal I have since noticed that when starting to transmit, there is a little blip of power, a pause, and then it starts transmitting. Not sure if that info helps, but defo seems strange.

Cheers

Matt

M0DQW

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[ron.ni...@gmail.com]

Can you try connecting to the HL2 directly via ethernet cable from a laptop run on battery power (no switch or router in between).  That would remove a few more conductive loops from the equation.  73, Ron, n6ywu

[Tech Minds]

@Steve 

Not sure if you saw my emails between Makerfabs and myself, but I have shipped the main board and the filter board to you today.  Please let me know once you have them

Many thanks

Matt

[Werner de Vos]

Matt, I'm having the same issue but listening to a webSDR the audio is fine. I've tested from HL2 <-> Yaesu FTDX10 and visaversa. Both way's the sound is distorted, so also the audio coming from the Yaesu.

So my advise would be, ask some hams further away to listen to your audio or pick a webSDR and record yourself.

Werner PA3GYV

Op vrijdag 7 juni 2024 om 22:28:22 UTC+2 schreef Tech Minds:

[Kurt V.]

Hi Matt,

I have had the same distortion when I listen to my voice on another radio in the shack when I TX with the HL2. Exactly the same. On that receiver (a Kenwood TS 480), I seem to get rid of this weird distortion just by adding a little screwdriver on the center of the SO plug. It seems for some reason it is more an issue with the receiver than with the transceiver or the HL2. 

Just plug anything in into your antenna plug of your receiver, and suddenly that weird audio goes to clear. Don't ask me why, but it seems the receiver is too close to the transceiver and it somehow interferes with the components inside the receiver. 

Another thing, Matt... I discovered that I had a humming sound in my audio. I got rid of it just by moving my OM 2000+ amplifier further away from the microphone. It seems the high voltage transformer is giving some magnetic field interference into my microphone. 

Hope to meet you one day on the air, so we can make a contact from HL2 to HL2. 

One more thing Mat, please, try the FDUCE SL40 microphone on your HL2; It is dirt cheap and boy, what a spendid audio this microphone gives on the HL2. Seems they are born to be together, the HL2 and the FDUCE SL40

Greetings and thanks for all the fantastic video's on YT.

De ON7OFF

Kurt

[Tech Minds]

Hi Kurt,

Thanks for the suggestions.

I did try an RSPdx pretty near to the HL2, but even on the lowest power setting on HL2 the buzz and the warbled SSB audio was present. So another test that I done was to connect a KiwiSDR up downstairs, away from the shack and just use a little telescopic antenna attached to the KiwiSDR. Exactly the same issues were observed.

I have now sent the HL2 and filter board to Steve and hopefully he will get a chance to look at it soon. Im sure Steve will be able to tell me if I have gone completely mad and the Hl2 is perfectly fine or whether there is a fault. 

I;ve had around 4 other HL2 in the past, and none of them experienced this issue. Unfortunately the ones that I had I gave to ham friends, and not so easy to get back to test here.

Cheers

Matt