Re: XV432 Oscillates with Amp connected

Posted by Thomas Ries on May 09, 2011; 10:11pm
URL: http://elecraft.85.s1.nabble.com/XV432-Oscillates-with-Amp-connected-tp6344925p6345858.html


Hello Stu2,

Some time ago, I had problems with an oscillating (or at the tip of
starting self-oscillation) XV432. It manifested in such a way, the XV432
being very sensitive to input power levels and "jumpy" output power when
adjusting the power level. Together with a Mirage D1010 (100W 70cm PA)
sometimes oscillation at full power has been observed.

In my case I could track it down to 70cm HF being coupled back into the
IF (TX IF towards the XV432) causing a feedback. I could eliminate the
oscillation by 2 modifications:

1) Added both the Elecraft Erratas to eliminate oscillation on the PA
   hybrid module (one is about installing a coil and a second one about
   installing a series resistor). Note that the errata to install the
   series resistor seems to superseede the coil, in my case installing
   both of the modifications did improve stability.

2) Install a small low-pass filter in the TX IF input in the XV432,
   as described here: www.dl7maj.de/XV432-Mod.pdf
   I installed the filter on board of the XV432, as shown in the
   PDF above. Note that I drive my XV432 from a K3 with 0dBm power.

With the above modifications no oscillation or instability in output
power has been seen anymore.

I hope this may help.

Best 73 de Thomas, HB9XAR

Stu2 wrote:

> Good day,
>
> I'm working with the XV432, Flex 1500 and Henry  2004A Amp. The rig,
> xvrtr and amp PTTs are sequenced. Hoping somebody might have been down
> this path before and has a solution.
>
> If I connect the transverter output to the amp (or different pieces of
> open coax) and key the transverter, the power meter goes full scale and
> I see an oscillation on the spectrum analyzer. The frequency of the
> oscillation varies with the load. (i.e. amp connected or different
> lengths of coax) If I connect the XV432 to a 50 ohm load, no
> oscillations and all works well.
>
> I ran through the alignment procedure again with the XV432 connected to
> a 50 Ohm load. All the voltages look right and the tuning is smooth.
> (e.g. 20mV Quiescent Current Adjustment, TP3/TP4) It's obvious the XV432
> is happy into 50 Ohms, but not into impedances that wander from 50 Ohms.
>
> BTW, I have added all the mods as per the Elecraft website.
>
> Any ideas?
>
> 73's
> Stu2
> W7IY
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