[CQ-Contest] SO2R audio spike problem

David A. Pruett k8cc at comcast.net
Fri Feb 6 18:09:07 EST 2004


I wonder if this has something to do with the fact that ICOMs have +8V on 
the mic pin of the radio for use with electret mics?  This voltage is not 
required for non-electret elements such as the Heil (either DX or 
standard), and indeed should be blocked with a capacitor of 0.22uF or greater.

The Heil ICOM adapter (from sub-mini jack to 8-pin plug) has the blocking 
capacitor built in.  If you've built the two-radio switch box just like the 
schematic, and you're plugging the Heil in directly, your mic is seeing 
+8VDC on it.  The "pop" you're hearing on switching may be caused when the 
mic connects, and loads down the +8V supply.

If one isn't present already, I would add a blocking capacitor at the jack 
where your Heil plugs into the switchbox.  This will block the +8VDC from 
getting both to the headset and the DVP.  The latter probably doesn't need 
the protection, as I'm pretty sure it's capacitively coupled.

The cap value is non-critical - anything over .22uF and rated for 8VDC or 
more is OK.  An electrolytic is OK too - I would put the + end towards the 



At 03:06 PM 2/6/04 -0500, Barkey, Patrick M. wrote:
>I've been running a pair of IC-765's with a N6TR-style
>two radio switch box for quite some time.  This is the
>one described in http://www.kkn.net/~k5tr/trlog/switch.pdf
>I have noticed on SSB for some time that whenever I
>switch between radios, the VOX on the radio I am
>switching towards pops.  I have a very short delay, so
>this is not a big deal.
>The problem is this.  Many times after switching my mike
>to radio #2 to work a multiplier, and then back to radio #1
>to call CQ, I loose audio output from my microphone
>and my DVP entirely.  It will be dead for about 5-10 seconds.
>If I leave the VOX off on both radios, this never happens.
>But I like to use VOX, so this isn't a great solution.
>I am using a Heil Pro-Set mike with a DX element.
>Anybody got any suggestions for a solution?  Thanks.
>   - Pat
>     N9RV
>     The world's top contesters battle it out in Finland!
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