[arm-allstar] Echo heard on Rx Audio

[Kevin Custer]

If those values are in degrees F - you'll be fine.  If the temperatures 
were getting to 140 degrees F - I'd start to worry about longevity.

Kevin


On 7/2/2023 4:20 PM, Dusty Smith wrote:
> Excellent advice. I changed that out this afternoon. Removed the high value inline resistors and added the 10k / 1k L network and the audio is still a little hot but perfectly manageable...more so than before and no more echo. Thanks a million for that advise.
>
> New question, more out of curiosity than anything. How hot would be too hot for the heatsinks on a transmitter...specially these CDM1250's. I've noticed during a long qso, the transmitter's heatsink temp is up around 115-120 degrees. After qso ends, it'll fall 10degrees pretty quickly, within a minute or two and continues to cool down from there. Just wondering about possible overheating problems and curious what the max safe temp range might be. Haven't been able to find any specifics on that in my initial searching.
>
>
> Dusty Smith
> —W4MSI—
>
> -----Original Message-----
> From: Kevin Custer <kevin at kc-wireless.com>
> Sent: Sunday, July 2, 2023 10:08 AM
> To: ARM Allstar <arm-allstar at hamvoip.org>
> Cc: Dusty Smith <w4msi at outlook.com>
> Subject: Re: [arm-allstar] Echo heard on Rx Audio
>
> Since you reference the discriminator audio is really hot - I'd conclude that it's leaking into the transmit audio directly because of cable cross-talk or another pseudo path.
>
> Instead of using a large series resistance to reduce the audio level, consider a L network where you have something like a 10k through resistor and a 1k to ground.  This will keep the audio path low impedance but accomplish necessary reduction without using high value resistors.  Put this resistance at the connector on the radio so it reduces cable cross-talk as well.
>
> Kevin
>
>
> On 7/1/2023 10:50 PM, Dusty Smith via ARM-allstar wrote:
>> Hello all, hoping to gather some info/pointers on where to look to try to solve this issue.
>>
>> I've had a repeater running with hamvoip on a pi4 for a good long while now...no major issues that I haven't been able to overcome at least thus far.
>> This evening I swapped out my radios on the repeater for some different/newer rigs.
>>
>> The old radios that have been working fine were Motorola Maxtracs and I've replaced them with some Motorola CDM1250 units.
>>
>> All seems to be pretty much equal on the surface, however, I've noticed that there is a reverb/echo on my Rx Audio. Any audio coming through links seems to be normal, but if I'm keying into the receiver of the repeater...then the output of the repeater has this echo. It's not a real loud echo, kinda faint, but it's definitely there and can be noticed especially if you are speaking louder. Others on the same frequency/repeater can hear it and if I do the parrot mode I can hear it.
>>
>> This wasn't here on the old radios. Same controller, same interface, etc......there is a new interface cable but it's made up the same way as the old one just different connections for the new radios. I've tried adjusting audio levels and such and if I turn it way down (simpleusb settings) then you can't hear the echo anymore, but the audio is just too low in general. So really the echo is probably still there you just can't hear it at that point. If I go into "alsamixer" and turn off automatic gain control, it seems to get better but it doesn't take it away entirely.
>>
>> One other note, the "flat/filtered rx audio" on pin 11 (where I'm getting my rx audio from on the back panel pinout of the CDM1250) seemed to be extremely hot audio. With it piped directly into my soundcard interface (modified usb fob) I could turn the rx audio level in simpleusb all the way down to 0 and it was still overmodulated by a lot. So I added in 2Mohms worth of resistance to the rxAudio line going from radio to interface (2 x 1Mohm resistors inline) and that got it down to a reasonable level.
>>
>> Ok I think that's all I can think to include in this question for now. If you need more info please ask. And thank very much in advance for any assistance.
>>
>>
>> Dusty Smith
>> -W4MSI-
>>
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