K3 Synthesizer Stiffener Plate Mod

[w0sz]

Has anyone installed the K3 Synthesizer Stiffener Plate Mod?  Do you think
this is an important Mod to install in an old K3?  Thanks for the
information.  Steve W0SZ

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[Bruce Beford-2]

Hi Steve.

 

I installed the stiffener plate mod on both synth boards in my K3, s/n 559.
It probably is only really needed if you run CW, with the internal speaker
on, and the sidetone turned up fairly loud. It is under those circumstances
that the speaker vibration can flex the synth board, causing some "chirp" or
other variability. You only actually need to do the main synth board. I
chose to do both, in case I ever swap the synth boards.

 

Bruce, N1RX

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[Jim Brown-10]

On Sun, 5 Sep 2010 17:55:15 -0600, W0SZ wrote:

>Has anyone installed the K3 Synthesizer Stiffener Plate Mod?  Do you think
>this is an important Mod to install in an old K3?  

If you transmit CW, RTTY, or PSK with the speaker on, vibrations from the
speaker can modulate the synthesizer at the frequency of your sidetone.
This produces sidebands that differ from your main signal by the sidetone
frequency(ies). This can be VERY serious -- it is a violation of FCC Rules,
it causes QRM, and it leads to confusion.

Several of us who are members of NCCC (Northern California Contest Club)
learned this the hard way last winter during the 10M contest, when we were
getting off-frequency responses to our CQs! Mostly contesters and CW ops
use headphones, but the 10M contest is one where you must call CQ for hours
on a dead band with no responses, hoping for a band opening. During that
time, you do things around the shack, etc., listening on the speaker. Many
of us also use the speaker when working RTTY during contests.

The band-aid fix for the problem is to use an external speaker that you
move away from the radio.

So the short answer is that if you work CW, RTTY, or PSK with sidetone
Monitor into the internal speaker turned on, this mod is VERY important.  

73, Jim K9YC


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