[Icom] 765 output spike

Thu, 13 Jun 2002 19:27:38 -0000

This is good information.  Thanks much for the post and congratulations on a
successful fix.

de Paul, W8AEF

----- Original Message -----
From: "Floyd Sense" <[email protected]>
To: <[email protected]>
Sent: Thursday, June 13, 2002 1:45 PM
Subject: Re: [Icom] 765 output spike

> In my recent query on this subject, I reported an output spike of 40-50
> watts when hitting the PTT switch in SSB mode.  While troubleshooting a
> separate problem, I discovered the cause of this one.  I access the audio
> in/out lines on the rig via the ACC-1 connector on the rear panel, and I
> feed the audio lines via mic cable to an interface box containing audio
> isolation transformers (used for PSK31 operation).  It turns out that the
> audio in and out lines at the ACC-1 connector are high impedance, and my
> wiring in the transformer box was a bit of a mess, resulting in coupling
> between the in/out audio lines and a bit of feedback.  Apparently during
the
> switch from receive to transmit, both are "on" for a short period and the
> feedback was driving the audio-in line causing the spike.  This feedback
was
> occuring without a speaker, earphones, or microphone attached to the rig.
>
> Redressing the lead lengths for the transformers reduced this coupling and
> completely eliminated the switching spike.  I now see no trace of output
> when the PTT line is activated without any audio drive.
>
> K8AC
>
> ----
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>