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[wxsig] MODEM2 Low TX audio

Joe S. Borovetz wa5vms at tapr.org
Wed Feb 15 19:51:41 UTC 2006

Sct599 at aol.com wrote:
> Hello Group:
> Adding a MODEM2 to my original T238.  I am connecting it to a ICOM  IC-2100 
> which should work with the separate Mic audio (TX audio) and  PTT lines (not 
> combined like an HT). The PTT and RX audio are working properly.  My TX audio is 
> very low even with adjusting V100.  The audio does change  with V100 
> adjustment but is still too low when even at max.  In my  troubleshooting of the audio 
> path I have noticed two things....
> 1. R101 is shown as a 10K on the schematic. However, the instruction manual  
> and parts list calls for a 100K.  A 100K was provided and is what I  have 
> installed. I jumpered past R101 and the audio did indeed increase but not  to an 
> acceptable level. What value should R101 be?
Change it to a 4.7 K and the output coupling capacitor from 100 pf to a 
.1 uf.

This should solve your problems.

> 2. V100 is supposed to be oriented on the board to match the  silkscreening.  
> However, if you do so, the leads are not oriented  properly.  I reversed V100 
> from the silkscreening to match the lead  arrangement and the photo at 
> _http://beals5.com/wx/index.htm_ (http://beals5.com/wx/index.htm)  under  "How to 
> build a T238+"  Does the orientation of V100 make a  difference?
> Any other ideas?
> 73,
> Scott
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