Hum On The Feed

[thinbluebbq]

I am chasing a hum that is in my feed I believe and that is in my radio room now too. I have isolated it to either the comm cable or the audio cable from my Uniden BCD325P2. I have a 3.5 mm audio cable running from my headphone jack on the Uniden to the mic input line on my desktop computer where I host the feed. I have a comm cable from the Uniden running into a USB port on the front of the desktop. Traditional Dell Optiplex Windows based computer. I have a very high pitched whine in the radio room and the audio from the radio won't play through my speakers attached to the computer. Additionally, I believe my feed sounds garbly and thick like there is a hum here. I would love any advice on how to get this hum to go away.

 

[Deziel0495]

A ground loop isolator may solve your issue. They can be found on amazon for less than $20.

 

[Reconrider]

You need a ground isolator. I got mine on amazon and use this one - buddy uses the same for his feed here on RR

Amazon.com: JABINCO Ground Loop Noise Isolator: for Car Audio/Home Stereo System with 3.5mm Audio Cable (Black): Car Electronics

Amazon.com: JABINCO Ground Loop Noise Isolator: for Car Audio/Home Stereo System with 3.5mm Audio Cable (Black): Car Electronics

www.amazon.com

 

[thinbluebbq]

Thanks for the advice. So I plug that device into the desktop and then the audio cable from my scanner into it, correct?

 

[doctordialtone]

That's it!

I use this one. Actually 3 of them!

 

[Deziel0495]

I use this one

I've got 2 of these, they work great.

 

[chipjumper]

I'm still getting a hum on my feed. Should I use more than one of those 3.5mm ground loop isolators?

 

[AB5ID]

I'm still getting a hum on my feed. Should I use more than one of those 3.5mm ground loop isolators?

That's more of a hiss with a very slight hum. How's your scanner connected to your computer?

 

[chipjumper]

Goes from the Radioshack scanner --> 3.5mm short cord to the ground loop isolator (the rectangle CHICOM one) --->raspberry pi. The power is supplied by an Eaton rack-mount 1500VA UPS that I thought did power conditioning in additional to UPS work. Maybe I should use one of those power strips have have a conditioning function? If I elimination the CHICOM ground loop isolator the hum is horrendous so I know that is working.

 

[AB5ID]

It sounds really good. If you're using the headphone or speaker output on the scanner the hiss may be coming from the audio amplifier in the scanner output or from the microphone input being too sensitive on the computer. If you can adjust the input sensitivity on the computer input try turning it down and turning the volume up on the scanner. An inline audio attenuator might also help. Here is a really cheap one: https://www.amazon.com/PChero-Extension-Adapter-Adjustment-Control/dp/B08T1YW1JK/

 

[chipjumper]

I never thought about doing that! I will grab that attenuator. Its easier to turn that little dial than fumble fart with the Raspberry Pi interface. Thank you. I'll report back here with my findings.

 

[iMONITOR]

Goes from the Radioshack scanner --> 3.5mm short cord to the ground loop isolator (the rectangle CHICOM one) --->raspberry pi. The power is supplied by an Eaton rack-mount 1500VA UPS that I thought did power conditioning in additional to UPS work. Maybe I should use one of those power strips have have a conditioning function? If I elimination the CHICOM ground loop isolator the hum is horrendous so I know that is working.

Does your UPS produce a true sine wave?

 

[AB5ID]

Another thing you can try is unplugging the audio in from the raspberry pi to make sure that the hiss goes away when there's nothing connected to the audio input. I had some hiss I could not get rid of but it was on a windows machine so I installed software that had a noise gate along with an audio compressor to finally get rid of the noise and keep the audio levels the same between different radio systems.

 

[chipjumper]

Interesting question iMONITOR. Its an Eaton so I think everything flows through the inverter regardless of the power status? I'll have to review the documentation. I like using Eaton as I once worked I.T. for a major ambulance firm in Michigan. We had catastrophic issues with APC UPS's as they would go bananas when they mechanically switched over. The Eaton's we started to buy had a seamless power transfer and would not overload the outdoor generator unit when it tried to come online.

AB5ID I will try unlplugging the audio to eliminate the scanner and CHICOM ground loop isolator.

 

[chipjumper]

Another thing you can try is unplugging the audio in from the raspberry pi to make sure that the hiss goes away when there's nothing connected to the audio input.

I just did this and the hiss+hum disappeared. Maybe its from the crappy wall wart that powers the scanner? I can try putting it on a 12V battery and see if that cleans it up (is there a RadioReference™ suggested brand or model power supply?) I will also order up that attenuation device.

 

[a417]

this is on a raspi running raspbian? ...and you've got the volume turned way the heck down on the RS scanner?

alsamixer --> select your sound card, go to "capture", and then adjust your gain. You might not need a physical attenuator at all. If your gain is up at the top, that's a super-hot mic you've got there...and it's going to amplify e v e r y t h i n g, including noise. If you roll the gain back down,and then have to turn up the volume on the scanner output, you might find better results.

I don't think your Eaton UPS has anything to do with this issue.

 

[KA0KDW]

Had that issue with my feed when I powered the scanner via the computer. I had to use a ground loop insulator and a usb sound card to get rid of the issue. If I wasn’t powering it via the computer I can just plug the audio cable directly into the line in and had no issue.

 

[chipjumper]

this is on a raspi running raspbian? ...and you've got the volume turned way the heck down on the RS scanner?

alsamixer --> select your sound card, go to "capture", and then adjust your gain. You might not need a physical attenuator at all. If your gain is up at the top, that's a super-hot mic you've got there...and it's going to amplify e v e r y t h i n g, including noise. If you roll the gain back down,and then have to turn up the volume on the scanner output, you might find better results.

I don't think your Eaton UPS has anything to do with this issue.

I think you solved the issue here. The capture was set to 44 and I dropped it to 19. I turned the volume up slightly. Here is the odd part, the feed went offline briefly and the alsamixer gain changed back to 44. I'm assuming darkice tanked. Is alsamixer supposed to retain the last settings or do I need to modify a file?

 

[chipjumper]

This definitely solved the problem. I actually dropped the gain down to 6. Its nearly silent now. Thank you! I just hope the alsamixer setting stays put upon an uncommanded restart...

 

[Kingscup]

I think you solved the issue here. The capture was set to 44 and I dropped it to 19. I turned the volume up slightly. Here is the odd part, the feed went offline briefly and the alsamixer gain changed back to 44. I'm assuming darkice tanked. Is alsamixer supposed to retain the last settings or do I need to modify a file?

If I remember correctly, it should be

sudo alsactl store