Hum while receiving on 20m?

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ki4pot
 

Posts: 10
Joined: 15 May 2022, 13:04

Hum while receiving on 20m?

Post by ki4pot »

With the radio tuned to 20m and powered by a battery, I get a nasty hum that sounds like AC hum. Any idea what could be causing that and how I can mitigate it? I don't hear this on 40m (the only other band I use).

Edit to add:
I just noticed it happens on all bands but 80m. As you go lower in frequency it becomes less noticeable, but is still there until you hit 80. This is while on battery power and without an antenna attached. I wasn't noticing it on the lower bands before because received signals often drowned it out, but without an antenna attached, it's definitely there on all but 80.

Chris
N6YWU
 

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Joined: 24 May 2022, 16:09

Re: Hum while receiving on 20m?

Post by N6YWU »

Do you hear this hum with an antenna attached? Or with a 50 Ohm dummy load?
What is the audio volume level? Are you using the internal speaker or headphones?
If the audio level is set above somewhere around 9 or so using the built-in speaker, microphonics (vibration or magnetic field from the small internal speaker feeding back into the electronics) can cause audible noise, buzz, or hum.
73, Ron, n6ywu
ki4pot
 

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Re: Hum while receiving on 20m?

Post by ki4pot »

N6YWU wrote: 06 Jun 2022, 15:30 Do you hear this hum with an antenna attached? Or with a 50 Ohm dummy load?
What is the audio volume level? Are you using the internal speaker or headphones?
If the audio level is set above somewhere around 9 or so using the built-in speaker, microphonics (vibration or magnetic field from the small internal speaker feeding back into the electronics) can cause audible noise, buzz, or hum.
73, Ron, n6ywu
With an antenna as well. I haven't tried with a dummy load. Since this is on receive and is present even without an antenna, I wouldn't expect a dummy load to matter.
Audio level is usually around 9 (never above 10). I use headphones.

I just tried it again and can hear the hum over the radio's noise floor (without an antenna) down to level 7. At 6 and below, the audio more or less completely cuts out except for some light crackling, so that's probably why the hum isn't evident at those levels.

Chris
dl6sez
 

Posts: 44
Joined: 30 Dec 2021, 22:54

Re: Hum while receiving on 20m?

Post by dl6sez »

Hello Chris,

i think you should compare it with the sound of the videos here, than you will know if it is normal (tr)uSDX sound or not. There are many video-links here in the general => video of.....
Remember (tr)uSDX is not an IC7300 ;) but it is an SDR :)
doing it's calculations on an 8-Bit non floating point capable 20MHz processor.

73 de Chris DL6SEZ
Chris DL6SEZ, JN48XL near Ulm, Southern Germany
ki4pot
 

Posts: 10
Joined: 15 May 2022, 13:04

Re: Hum while receiving on 20m?

Post by ki4pot »

dl6sez wrote: 06 Jun 2022, 17:02 Hello Chris,

i think you should compare it with the sound of the videos here, than you will know if it is normal (tr)uSDX sound or not. There are many video-links here in the general => video of.....
Remember (tr)uSDX is not an IC7300 ;) but it is an SDR :)
doing it's calculations on an 8-Bit non floating point capable 20MHz processor.

73 de Chris DL6SEZ
It was listening to the other videos that led me to believe the sound is abnormal. I'll try to get a recording of it tomorrow.

Chris
dl6sez
 

Posts: 44
Joined: 30 Dec 2021, 22:54

Re: Hum while receiving on 20m?

Post by dl6sez »

Hello Chris,

okay, there is one other possibility i forgot: do you have a strong AM Station or a Mobile TRX anywhere in the near of your listening place? The SDR is not really protected with his PLA or other 3D printer friendly plastic case and it is from the RF few a direct sampling circuit.
You could probably have a bad solder joint on Si5351, which i once had with a very strong nice Motorboating sound :x
Would be interesting to hear how it sounds, it's a good idea to record it.

73 de Chris DL6SEZ
Chris DL6SEZ, JN48XL near Ulm, Southern Germany
radioguy
 

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Joined: 05 Mar 2022, 07:42

Re: Hum while receiving on 20m?

Post by radioguy »

FWIW.......I've noticed the same thing......JUST as you described it (with or without an antenna)......mainly on 20. I have to admit, however, that it is not ALWAYS there. It's not a 60 cycle hum but it does sound similar.

The little radio does have some anomalies but it does work. I don't use it in "the field" but I do play with it quite a bit at the home station using my tri bander and open wire fed 80M dipole. I regularly work all over Europe and even Hawaii on 20 SSB.....from NJ..... haven't even tried it yet on CW but it sounds very clean. When 20 is open even 5 watts gets thru......with no problems. Just a toy......for when using a kilowatt gets old. I guess I'm cheating a little using the big antennas.....but I don't lose any sleep over it ...LOL.

radioguy
ki4pot
 

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Re: Hum while receiving on 20m?

Post by ki4pot »

dl6sez wrote: 07 Jun 2022, 06:32 Hello Chris,

okay, there is one other possibility i forgot: do you have a strong AM Station or a Mobile TRX anywhere in the near of your listening place? The SDR is not really protected with his PLA or other 3D printer friendly plastic case and it is from the RF few a direct sampling circuit.
You could probably have a bad solder joint on Si5351, which i once had with a very strong nice Motorboating sound :x
Would be interesting to hear how it sounds, it's a good idea to record it.

73 de Chris DL6SEZ
Unfortunately I wasn't able to record the sound in a way that came through. While I could hear it clearly, my phone wasn't picking it up.

There are no strong transmitters nearby, but the neighborhood is densely populated and there are many many normal household devices (wifi routers, etc) emitting RF. I'm going camping this weekend and will be up in the mountains, so I'll try it there to see if it's environmental in nature. I've already gone through the rig looking for poor solder joints, aside from a couple questionable ones on toroids, things looked pretty decent.

Chris
ki4pot
 

Posts: 10
Joined: 15 May 2022, 13:04

Re: Hum while receiving on 20m?

Post by ki4pot »

radioguy wrote: 07 Jun 2022, 09:33 FWIW.......I've noticed the same thing......JUST as you described it (with or without an antenna)......mainly on 20. I have to admit, however, that it is not ALWAYS there. It's not a 60 cycle hum but it does sound similar.

The little radio does have some anomalies but it does work. I don't use it in "the field" but I do play with it quite a bit at the home station using my tri bander and open wire fed 80M dipole. I regularly work all over Europe and even Hawaii on 20 SSB.....from NJ..... haven't even tried it yet on CW but it sounds very clean. When 20 is open even 5 watts gets thru......with no problems. Just a toy......for when using a kilowatt gets old. I guess I'm cheating a little using the big antennas.....but I don't lose any sleep over it ...LOL.

radioguy
It does have some quirks. I'm not expecting perfection, I already have a KX2 for critical portable ops, but I would like to polish this one more over time. I've had a few QSOs with it already, so it certainly works.

Chris
ki4pot
 

Posts: 10
Joined: 15 May 2022, 13:04

Re: Hum while receiving on 20m?

Post by ki4pot »

Couple updates...

I hear the noise in any location (even in the deep mountains away from any other transmitters).
The noise is worse on USB/LSB, but not noticeable on CW.
It's apparent on all the bands, but very bad on 20m.

Chris
virhao
 

Posts: 7
Joined: 31 Dec 2021, 05:46

Re: Hum while receiving on 20m?

Post by virhao »

Go to menu 1.9 and listen if this noise is the same in my case noise is dependent on how much display i displaying and menu 1.9 have the least to display and i am always transmitting and receiving being in that menu option
Last edited by virhao on 02 Aug 2022, 16:29, edited 1 time in total.
ki4pot
 

Posts: 10
Joined: 15 May 2022, 13:04

Re: Hum while receiving on 20m?

Post by ki4pot »

The noise is reduced on the menus with less displayed text, so it's clear the noise is from the display.

Maybe the 8v mod described here is a partial fix?
viewtopic.php?p=2968#p2968

Chris
dl6sez
 

Posts: 44
Joined: 30 Dec 2021, 22:54

Re: Hum while receiving on 20m?

Post by dl6sez »

Hello OM,

maybe you haven't done the OLED display mod, which disables the charge pump in the OLED?
This belongs to standard assembly as DL2MAN shows in his video and is so far not an extra mod.
There is no 8V mod needed, normally the 5V are used directly from the (tr)uSDX itself.
They only use 8V because of the not so bright OLEDs with 5V.
So if the charge pump wasn't disabled at your OLED this would explain the harsh Noise....
You will still here a little bit of Noise with mod to 5V or 8V but it is really not comparable with no mod.

73 de Chris
Chris DL6SEZ, JN48XL near Ulm, Southern Germany
ki4pot
 

Posts: 10
Joined: 15 May 2022, 13:04

Re: Hum while receiving on 20m?

Post by ki4pot »

dl6sez wrote: 02 Aug 2022, 14:00 Hello OM,

maybe you haven't done the OLED display mod, which disables the charge pump in the OLED?
This belongs to standard assembly as DL2MAN shows in his video and is so far not an extra mod.
There is no 8V mod needed, normally the 5V are used directly from the (tr)uSDX itself.
They only use 8V because of the not so bright OLEDs with 5V.
So if the charge pump wasn't disabled at your OLED this would explain the harsh Noise....
You will still here a little bit of Noise with mod to 5V or 8V but it is really not comparable with no mod.

73 de Chris
No, I haven't yet. I bought mine assembled from the approved vendor at AliExpress and am now working to sort out the rig. I thought the 8v mod would be the fix since the author mentioned it reduced the noise. Is there a link to just the charge pump mod?

Chris
RichardB
 

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Joined: 15 May 2022, 01:37

Re: Hum while receiving on 20m?

Post by RichardB »

Check DL2MAN assembly page - https://dl2man.de/2-trusdx-assembly/

The video, around the 9:20 time mark is where he talks about the display mod.

Richard
ki4pot
 

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Joined: 15 May 2022, 13:04

Re: Hum while receiving on 20m?

Post by ki4pot »

RichardB wrote: 02 Aug 2022, 23:20 Check DL2MAN assembly page - https://dl2man.de/2-trusdx-assembly/

The video, around the 9:20 time mark is where he talks about the display mod.

Richard
It looks like that mod was done to mine, so the problem is elsewhere. :?

Chris
dl6sez
 

Posts: 44
Joined: 30 Dec 2021, 22:54

Re: Hum while receiving on 20m?

Post by dl6sez »

Hello OM,

can you please record the sound and post it here?
It doesn't have to be a video...makes no sense.... but the sound :)

73 de Chris
Chris DL6SEZ, JN48XL near Ulm, Southern Germany
ki4pot
 

Posts: 10
Joined: 15 May 2022, 13:04

Re: Hum while receiving on 20m?

Post by ki4pot »

dl6sez wrote: 05 Aug 2022, 10:45 Hello OM,

can you please record the sound and post it here?
It doesn't have to be a video...makes no sense.... but the sound :)

73 de Chris
I've tried in the past but can never seem to get a recording that makes the sound clear. It sounds very much like 60hz AC hum and directly related to the screen content (more text, more noise). It goes away when in CW mode and gets less noticeable as you go down in frequency (undetectable in 80m, barely detectable in 40m, obnoxious in 20m).

Chris
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