Headphone o/p noise on transmit

EI2HH
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Headphone o/p noise on transmit

Postby EI2HH » Mon Sep 28, 2020 10:01 am

This is a strange one, I find with my Anan 7000DLE, on transmit the headphone connection, supposedly muted, outputs some noise.

This is a kind of digital-sounding hiss/hum, which to the uninitiated sounds like a fan running in the background.

Its a problem for me because of the way I route the audio; My audio comes from a mixer to the Apache, and the output of the Apache is fed to a channel on the mixer, fader up all the time, so that in my headphones/speakers I hear the rx audio when receiving, but when transmitting I hear myself, clean.

Trouble is, this noise coming from the hph output during tx, albeit at low level, gets picked up and amplified by the audio processor I use (which is after the mixer), so to the 'audience' it sounds like I have a noisy fan running in the background. To stop it I have to put the Apache fader down each time I tx, then raise it again when keying down, which is annoying.

Is this is 'thing', that they all do? Is there a setting that could reduce this? Any thoughts? I don't believe its RFI, as the level of the noise doesn't alter with RF output level.

Please don't suggest that I connect everything differently as I have specific reasons for doing this!

Thanks

Andy EI2HH
Last edited by EI2HH on Mon Sep 28, 2020 11:44 am, edited 1 time in total.
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w-u-2-o
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Re: o/p noise on transmit

Postby w-u-2-o » Mon Sep 28, 2020 11:42 am

Andy, I don't have an answer for you, but you might edit your post title to use the word "headphone" so it is easier to understand.

I use VAC exclusively and have literally never used the headphone jack, and can't since the hardware is two stories below my operating position. It's tempting to point the finger at RFI, though.
w9mdb
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Re: Headphone o/p noise on transmit

Postby w9mdb » Mon Sep 28, 2020 1:31 pm

Please describe your shack grounding system in detail. Hum is frequently caused by different ground potentials.
I've had to help a number of people who stuck a rod in the ground outside their shack without grounding it to the house ground (doing it outside the house). Simply having them use the house ground instead solved their problems of RFI and hum.
You should also check the shield on your mixer jack to see if it's grounded to the case.

Mike W9MDB
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EI2HH
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Re: Headphone o/p noise on transmit

Postby EI2HH » Mon Sep 28, 2020 2:04 pm

Each piece of equipment is grounded by a separate cable to a central point, which is then connected to a couple of ground rods.

But this does not sound like a ground loop. It sounds like a digital hash with a slight high frequency hum, not 50Hz (which we use here).

Here's a recording - this has been amplified by 10dB:

https://soundcloud.com/andy-linton/apache-noise/s-0sI9CEEFBVE
Last edited by EI2HH on Mon Sep 28, 2020 2:22 pm, edited 1 time in total.
w9mdb
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Re: Headphone o/p noise on transmit

Postby w9mdb » Mon Sep 28, 2020 2:20 pm

And what are your "couple of ground rods" connected to ? The house ground rod too?
If not that is an electrical code violation and bad idea to boot for RFI control.

Mike
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EI2HH
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Re: Headphone o/p noise on transmit

Postby EI2HH » Mon Sep 28, 2020 2:23 pm

It is also connected to the house ground.

And since I'm in Ireland I'm not bound by US electrical code.

And as I said, I don't believe its RF feedback, as it's irrelevant to the OP power. In the recording above, the Apache is on SSB, there is no audio being fed to it, therefor its not actually transmitting anything, but is 'in' transmit mode.
w9mdb
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Re: Headphone o/p noise on transmit

Postby w9mdb » Mon Sep 28, 2020 2:34 pm

That audio does sound like a fan running.
So what happens when you unplug the mic?
Does the headphone jack on the rig have the same noise?
Is your mixer grounded?

Mike
Mike W9MDB
EI2HH
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Re: Headphone o/p noise on transmit

Postby EI2HH » Mon Sep 28, 2020 2:38 pm

That is with the audio input to the tx disconnected, audio taken from the headphone output, Apache MOX on.

Mixer is grounded like everything else, all interconnecting cables are balanced, with an isolation transformer on the audio input. But like I say, that's with no mic or audio input connected.

A
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w-u-2-o
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Re: Headphone o/p noise on transmit

Postby w-u-2-o » Mon Sep 28, 2020 5:59 pm

EI2HH wrote:Here's a recording - this has been amplified by 10dB:

https://soundcloud.com/andy-linton/apache-noise/s-0sI9CEEFBVE

Is that with or without the post processing?

If it is with post processing, would you please post a recording of the raw output at 0dB gain?

Note that you can attach the file directly to your post using the "attachments" tab below the main post editing window.

edited to add: dumb question: if you disconnect the cable from the ANAN and then transmit, do you still get the noise?
EI2HH
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Re: Headphone o/p noise on transmit

Postby EI2HH » Tue Sep 29, 2020 8:04 am

No processing on that, just +10dB. And that's with no audio cable connected to inputs.
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Re: Headphone o/p noise on transmit

Postby w-u-2-o » Tue Sep 29, 2020 2:32 pm

Is the noise present when you pull the cable out of the ANAN headphone jack?
EI2HH
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Re: Headphone o/p noise on transmit

Postby EI2HH » Tue Sep 29, 2020 2:55 pm

How would I know? Thats where I'm hearing it from.
laurencebarker
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Re: Headphone o/p noise on transmit

Postby laurencebarker » Tue Sep 29, 2020 4:11 pm

Do you have MON selected (at the top left)? If that's selected, your headphone output will be fed from the TX audio, re-received and downconverted. If there was any noise from the microphone, that would then potentially be present in the headphone audio.

If MON is selected: do you get the same sound with it turned off?

You've said you are hearing this noise at the output of a mixer, if I understand correctly. It would be useful to know if the same noise is present directly on the headphone output of the radio hardware: that would help to track down whether it has been introduced in the radio hardware or after the radio.
Laurence Barker G8NJJ
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w-u-2-o
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Re: Headphone o/p noise on transmit

Postby w-u-2-o » Tue Sep 29, 2020 5:31 pm

EI2HH wrote:How would I know? Thats where I'm hearing it from.

Not necessarily. You are hearing it from your headphones. Where it is being sourced or introduced from has not yet been established.

If you pull the cable out of the ANAN headphone jack, then transmit, and you still hear the sound in your headphones, then the noise is not coming from the ANAN.

Laurence is making the same suggestion I am but proposing a different method to arrive at the same answer: where is the noise coming from and/or being introduced?
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Re: Headphone o/p noise on transmit

Postby w-u-2-o » Tue Sep 29, 2020 6:21 pm

I just tried this on my 8000, which is the same as the 7000 in that they both use the Orion MKII SDR board and thus share the same audio and SDR circuitry. I plugged headphones into the front panel jack, cranked the Master AF to 100, and could discern no noise on the output during transmit.

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