[App_rpt-users] Noisy Sound FOBS

Jim Duuuude telesistant at hotmail.com
Thu Feb 23 01:21:58 EST 2012

Did you use the sleeve of the mic input as the GND reference, or did you make the
(often smokey) mistake of even connecting to the sleeve of the headphone output,
which, if the chip didnt blow up from being shorted is at VCC/2??


Date: Wed, 22 Feb 2012 21:15:15 -0800
From: n6gkj.cm98 at yahoo.com
To: app_rpt-users at ohnosec.org
Subject: [App_rpt-users] Noisy Sound FOBS

Hey guys,

I just got in some really cheap CM108 type sound FOB's from China, they work, I use the DSP for COR and CTCSS with the DB25 pins for ptt. However, I am hearing some really noisy sound when I access this node. I setup a DMK URI on the same node, no noise. 

Has anyone encountered this before?

Is it the cheap sound FOB's or is there something else I need to do.

I have my audio voitage divider feeding the RX Input, I have that fed by a 10uf cap. No DC bias on the chip. I am feeding the FOB with a VHF Maxtrac 300 discriminator audio, JU551 in position A. plenty of audio, PL detect and COR is very reliable. I use this as a RX only node. A very simple hardware configuration.

Any ideas?

Ron Simpson,

N6GKJ Amateur Radio


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it is always found in the last place you look?
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