[arm-allstar] Open board cm108 sound fobs

[David McGough]

Hi Alan,

Is this a case where the RX audio with the fob was originally okay and is 
now too low?  ...Or, a case where the audio was always low? (I think the 
latter case....)

If the audio was initially okay and is now bad, I expect either a 
connection is failing or the you've got hardware failure.

If the audio was always low, we've run into some cm1xy series chips that
have really low RX (cm1xy mic input) audio; sometimes 20db below "normal"  
chips! It also seems that most (all?) of the "B" series chips (like:  
cm119b) have very low audio.

I don't really have an explanation for why the significant audio level 
variation, particularly in the real c-media "B" series chips, the data 
sheet doesn't indicate there should be any difference, hardware wise.

I know there are several hardware builders out there that monitor this 
list, they may want to elaborate further??

Anyhow, I have a simpleusb patch to boost or attenuate the audio levels 
digitally, but it's not released in the main code. The problem with 
boosting the gain this way is that it also boosts the noise floor, which 
is obviously undesirable.

The best solution is to avoid the fobs that have low audio, or use an 
audio pre-amp stage. Another possibility might be to pick up the RX audio 
from a different spot in the radio.

What type of fob do you have?

73, David KB4FXC


On Thu, 3 Aug 2017, "Alan Matthews via arm-allstar" wrote:

> Guys

I have been using the open board style cm108 sound fobs from china to build my nodes. I have noticed recently that the tx audio into the system (what you hear on your end) is very low.

When running the simple usb tune option 2 i cannot get the audio level  to get anywhere near the markers.

when using the baofeng bf888s its not to bad, however connected to my ft991 or 7800 the levels are extremely low. I never had this problem with startech fobs. 

My URI fob works great with the 991. 

Have any of you guys experienced this issue.

thanks in advance.

regards Alan
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