Whining Sound While Receiving on Portables

[kenwoodgeek]

I have a couple Kenwood portables at work, one of them being a TK-3173 and the other being a TK-3312, that make a terrible, low pitch whining or squealing sound while receiving. They do it on and off, and the volume of the noise sometimes changes, but it is so overpowering it makes it difficult to hear the transmission. They transmit perfectly fine.

Anyone know what the cause and fix is for this? One of them had a broken whip with the coil partially exposed, but I'm not sure if that would have anything to do with it. I won't buy a replacement whip if that won't fix it. The radios are old and in poor shape. I want to see if I can get them going to save money; otherwise we'll just replace them.

Thanks!

 

[RFI-EMI-GUY]

if you move the radios to another location does the sound go away...?

 

[mmckenna]

I had a mobile that seemed to do that. Funny thing was the whining noise went away when my wife wasn't riding with me.

But seriously, folks….

Is it a low rumble, or is it higher pitch noise?

 

[kenwoodgeek]

if you move the radios to another location does the sound go away...?

It does seem that way. They were both being carried by a bus mechanic being used back in the shop. I moved one of them up to the dispatch office, and it was alright for a few minutes, and then it started doing it again.

 

[kenwoodgeek]

I had a mobile that seemed to do that. Funny thing was the whining noise went away when my wife wasn't riding with me.

But seriously, folks….

Is it a low rumble, or is it higher pitch noise?

Huh, that is interesting! Haha. It's somewhere in between. Almost like a low pitch feedback noise or tone.

 

[mmckenna]

If it does it consistently, there's one explanation:
If the repeater output is using a really high PL tone, like upwards of the 250Hz range, it can make it through the radio and into the audio path. That presents as a constant low rumble sound in the received audio. Usually there is some audio filtering that eliminates that. Some radios it's designed in and permanent, some radios have it as a "low cut" option.

But that doesn't sound like what you are hearing.

If the antenna is all jacked up, then its likely the radio gets a lot of abuse. Getting knocked around a lot can result in a number of issues I've seen:

-Big one is that metal particles will collect around the speaker. This is common in construction, maintenance or even for a mechanic. Those little pieces of steel/iron get attracted to the magnet in the speaker and will rattle around when the radio is receiving and make all kinds of weird noises. Cleaning it out will fix it, but getting the magnet in the speaker to release it's grip-o-death on those metal particles can be extremely difficult. Sometimes a stronger magnet can help convince them to jump ship and stick to the stronger one.

-Damage to the radio. Stuff comes loose and rattles around. Check for cracked case, loose speaker, etc.

-Usually on transmit, but there can be a situation called "microphonics" where the audio can get RF into it, and that results in all kinds of awful noises. Often it's on the transmit side as it needs the RF to cause it.

 

[kenwoodgeek]

If it does it consistently, there's one explanation:
If the repeater output is using a really high PL tone, like upwards of the 250Hz range, it can make it through the radio and into the audio path. That presents as a constant low rumble sound in the received audio. Usually there is some audio filtering that eliminates that. Some radios it's designed in and permanent, some radios have it as a "low cut" option.

But that doesn't sound like what you are hearing.

If the antenna is all jacked up, then its likely the radio gets a lot of abuse. Getting knocked around a lot can result in a number of issues I've seen:

-Big one is that metal particles will collect around the speaker. This is common in construction, maintenance or even for a mechanic. Those little pieces of steel/iron get attracted to the magnet in the speaker and will rattle around when the radio is receiving and make all kinds of weird noises. Cleaning it out will fix it, but getting the magnet in the speaker to release it's grip-o-death on those metal particles can be extremely difficult. Sometimes a stronger magnet can help convince them to jump ship and stick to the stronger one.

-Damage to the radio. Stuff comes loose and rattles around. Check for cracked case, loose speaker, etc.

-Usually on transmit, but there can be a situation called "microphonics" where the audio can get RF into it, and that results in all kinds of awful noises. Often it's on the transmit side as it needs the RF to cause it.

Thank you! I just noticed that, at least on the 3312, it only does it for me if the volume is cranked up to the max. I could see it being metal particles on the speaker. The mechanics need their radios cranked up to the max, usually, especially with the loud bus engines.

I got a recording of the noise and uploaded it in a video. Here it is.

I rebuilt this 3312 from three different units that were broken, and it has been beaten to crap since then, so I think she's about ready to be replaced and go in my parts bin. Possibly the same for the 3173.

 

[bharvey2]

Thank you! I just noticed that, at least on the 3312, it only does it for me if the volume is cranked up to the max. I could see it being metal particles on the speaker. The mechanics need their radios cranked up to the max, usually, especially with the loud bus engines.

I got a recording of the noise and uploaded it in a video. Here it is.

I rebuilt this 3312 from three different units that were broken, and it has been beaten to crap since then, so I think she's about ready to be replaced and go in my parts bin. Possibly the same for the 3173.

I run in to similar problems. Given that we operate around loud equipment, employees like to have the volume cranked up to 11. The three most common problems I encounter that create similar symptoms of a buzzing sound are: cracked solder connections of volume pots, blown speakers and as mmckenna mentioned, metal particles stuck in the speaker grill. I have to repair one of the problems on a radio at last once a week. I just did a solder repair this morning. Then there are the guys who drop their radios and run them over with a forklift. That creates a different noise: the sound of a "butt chewing" from their manager. Had one of those at the beginning of the week.

 

[mmckenna]

Thank you! I just noticed that, at least on the 3312, it only does it for me if the volume is cranked up to the max. I could see it being metal particles on the speaker. The mechanics need their radios cranked up to the max, usually, especially with the loud bus engines.

I got a recording of the noise and uploaded it in a video. Here it is.

I rebuilt this 3312 from three different units that were broken, and it has been beaten to crap since then, so I think she's about ready to be replaced and go in my parts bin. Possibly the same for the 3173.

That sounds like something wrong in the audio chain of the radio.

If you had the time and a service monitor, you might be able to track it down and fix it.
If not, then I'd say that radio has lived a full and productive life and has earned it's retirement.

 

[bharvey2]

That sounds like something wrong in the audio chain of the radio.

If you had the time and a service monitor, you might be able to track it down and fix it.
If not, then I'd say that radio has lived a full and productive life and has earned it's retirement.

+1 on your diagnosis. After watching the video, I notice the noise even when there is no deviation (audio) present. The other issues mentioned above would only show up when there is audio. It's time to retire the radio.

 

[mmckenna]

Thanks.

Yeah, if it's just this one radio doing that, somethings gone wonky with that radio. If it did it on all your radios, it'd be time to look at the repeater or any wireline links.