Re: XV432 Oscillates with Amp connected

Posted by Colin VE3MSC on May 11, 2011; 11:23pm
URL: http://elecraft.85.s1.nabble.com/XV432-Oscillates-with-Amp-connected-tp6344925p6353970.html


Stu - Three more suggestions:
- remove the paint along the inside edges of the box where the lids
meet the box sides and the C shaped front/back panels, and remove the
paint under the screw heads (I used a dremel bit to grind a nice
circle under the head).
  - try increasing the PA Bias a bit, so that you are reading 30-40mV
instead of 20mV at the test points TP3/4. Gary S suggested this.
- replace the grey heatsink thermal pads with Thermalcote conductive
heatsink grease.  In my case, this stabilized the power output over
time, as well as improved the output instability.

I also had done the PCBoard mod to ground top/bottom sides near the
relay down in front, suggested by someone else.

I was able to work a handful for the spring sprint - including Steve
VE3SMA - as a result of these changes.

Good luck
Colin Haig VE3MSC

At 07:19 PM 2011-05-10, Stu2 wrote:

>Thanks guys!
>
>It's quite weird. When I say key up, I mean activate the XV432 PTT with
>the rig (exciter) in CW mode without pressing the CW key.  That is, no
>RF goes into the transverter. Just the simple fact of keying the
>transverter while it is connected to something other than a 50 Ohm load
>seems to set up an oscillation.
>
>Several people have suggested a pad. The output of the XV432 is a low
>pass pi circuit. Since I don't want to reduce the RX gain, it would seem
>this either needs to be in the amp's TX chain or the XV432's TX chain.
>(i.e. before the TR relay)
>
>After I wrote my first message, I installed an SWR meter between the
>XV432 and amp so I could adjust the Henry for the best SWR.
>Unfortunately, this didn't cure the problem. The XV432 still oscillated.
>I have another amp I can try. I also have a TS2000 to try to help set
>the amp up.
>
>Thanks again for the ideas.
>
>Stu2
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