[CQ-Contest] Voice Keyer

[kl7ra]

Dave, K8CC  writes:

>Its been my experience that ICOMs are the worst in terms of humming from 
>unisolated mic grounds.  For these, I got a small mini-box with input and 
>output connectors and wired a Radio Shack 600:600 isolation transformer to 
>these connectors.  Oh yeah, you need a small capacitor (a 1uF/15V 
>electrolytic will do) between the transformer and the output connector to 
>isolate the +8V that is superimposed on the ICOM mic lead.  This combo 
>(MFJ-432 and isolation box) has worked perfectly on five or six different 
>ICOM models on which it was tried.

Another solution is to remove the Ground from the wiper of  RY1 relay and 
replace it with a wire going back to the radio pinout PTT Gnd. This will also
isolate the Gnds. MFJ made several flavors of the 432 and later ones have
FETs in place of the RY1 relay so they may have fixed the problem. Can't
tell for sure as they don't give you a schematic any more. 

The W9XT card does have a .22 cap, C3, installed on pin 17 mic input of 
the ISD-1016A voice keyer. This is a problem as the new Heil headsets
for Icom come with an electret mic and need the DC. The MFJ provides
MIC DC power and the new headsets work fine with them. I modified my 
SO2R box that routes MIC to the W9XT card and back to the radios to 
provide DC while recording.

By the way the new Heil headset for Icom is their final fix as the VOX will
now work, smooth as silk. Also requires their Icom adapter without the DC 
blocking.

I have three W9XT cards and three MFJ keyers for Muli-Multi. The W9 required
some RFI work to be able to record during the contest. The MFJ required mods
as Dave, K8CC  mentions to work with IC-781 radios.  

   
73 Rich  KL7RA     Latitude with attitude...


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