XV432 Oscillates with Amp connected

[Edward R Cole]

First off let me state that I do not have any of the equipment Stu is
using.  The fact the XV432 likes the 50-ohm termination (dummy load
to the rest of us), says it looks like a termination loading
issue.  The Henry 2004 should offer a 50-ohm load at input.  Some
amps require input tuning (my 2m-8877 is very touchy on input tuning
and does not present a low SWR; best I get is 1.7:1).  My amp is HB
so I know why.  Transmitting into open unterminated coax will
normally show standing wave peaks and valleys.  But perhaps the XV432
is going into self-oscillation when not seeing a good load?

If you have enough excess power I would suggest using a 3-dB
attenuator between the XV432 and Henry amp.  It will have to be rated
for full power of the XV432.  Many amps even have an internal
attenuator on the input (mainly to broadband input tuning).

Do you have another 432 transmitter to test with the Henry
amp?  Also, try different lengths of coax between the XV432 and the
amp.  Oh, and test those coax lines with the 50-ohm termination on
the far end (should see no oscillation or SWR).

If the XV432 is going into self-oscillation it might be RF feedback
from the Henry amp thru power lines?  Try moving the XV432 dc cables
to see if that causes any effect.  If so wrapping the dc cord thru a
toroid core may help (also check that there is RF bypassing inside
the XV432 on the dc input.  Should see a bypass cap and maybe
ferriite beads on the dc line.  Check station grounding.  That Henry
needs a good RF and safety ground to an external ground post and
house wiring ground (this has been a recent topic).

Have you tested with the Henry into a 50-ohm termination (dummy
load)?   High SWR on the antenna can also produce these effects with
a high-power amp.  (of course no all of us have a QRO dummy load)  I
have a 500w Sierra Electronics air cooled load that will sustain up
to 1000w for quick checks (no sustained key-down).  At 1500w, I
usually use my 2m eme array as best load (on a clear freq.).

GL, Ed - KL7UW

------------------------------

Message: 2
Date: Sun, 08 May 2011 13:34:55 -0400
From: Stu2 <[hidden email]>
Subject: [Elecraft] XV432 Oscillates with Amp connected
To: [hidden email]
Message-ID: <[hidden email]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

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





73, Ed - KL7UW, WD2XSH/45
======================================
BP40IQ   500 KHz - 10-GHz   www.kl7uw.com
EME: 50-1.1kW?, 144-1.4kw, 432-100w, 1296-testing*, 3400-?
DUBUS Magazine USA Rep [hidden email]
======================================
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[Thomas Ries]

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
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

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[M Cresap]

I had a similar problem with my XV432. I was able to chase the problem to the tx
driver stage. The fix was to add ground vias from the top to the bottom of the
board in a few judicious places. I passed this info back to Gary at Elecraft. I
know of at least one other XV432 that has been stabilized by this method. I
don't see those mods in the latest XV432 errata sheet, perhaps they vias have
been added to the latest circuit board or they have found other ways to cure the
problem.

73, Mike, W3IP




________________________________
From: Edward R. Cole <[hidden email]>
To: [hidden email]
Sent: Mon, May 9, 2011 12:46:11 PM
Subject: [Elecraft] XV432 Oscillates with Amp connected

First off let me state that I do not have any of the equipment Stu is
using.  The fact the XV432 likes the 50-ohm termination (dummy load
to the rest of us), says it looks like a termination loading
issue.  The Henry 2004 should offer a 50-ohm load at input.  Some
amps require input tuning (my 2m-8877 is very touchy on input tuning
and does not present a low SWR; best I get is 1.7:1).  My amp is HB
so I know why.  Transmitting into open unterminated coax will
normally show standing wave peaks and valleys.  But perhaps the XV432
is going into self-oscillation when not seeing a good load?

If you have enough excess power I would suggest using a 3-dB
attenuator between the XV432 and Henry amp.  It will have to be rated
for full power of the XV432.  Many amps even have an internal
attenuator on the input (mainly to broadband input tuning).

Do you have another 432 transmitter to test with the Henry
amp?  Also, try different lengths of coax between the XV432 and the
amp.  Oh, and test those coax lines with the 50-ohm termination on
the far end (should see no oscillation or SWR).

If the XV432 is going into self-oscillation it might be RF feedback
from the Henry amp thru power lines?  Try moving the XV432 dc cables
to see if that causes any effect.  If so wrapping the dc cord thru a
toroid core may help (also check that there is RF bypassing inside
the XV432 on the dc input.  Should see a bypass cap and maybe
ferriite beads on the dc line.  Check station grounding.  That Henry
needs a good RF and safety ground to an external ground post and
house wiring ground (this has been a recent topic).

Have you tested with the Henry into a 50-ohm termination (dummy
load)?  High SWR on the antenna can also produce these effects with
a high-power amp.  (of course no all of us have a QRO dummy load)  I
have a 500w Sierra Electronics air cooled load that will sustain up
to 1000w for quick checks (no sustained key-down).  At 1500w, I
usually use my 2m eme array as best load (on a clear freq.).

GL, Ed - KL7UW

------------------------------

Message: 2
Date: Sun, 08 May 2011 13:34:55 -0400
From: Stu2 <[hidden email]>
Subject: [Elecraft] XV432 Oscillates with Amp connected
To: [hidden email]
Message-ID: <[hidden email]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

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





73, Ed - KL7UW, WD2XSH/45
======================================
BP40IQ  500 KHz - 10-GHz  www.kl7uw.com
EME: 50-1.1kW?, 144-1.4kw, 432-100w, 1296-testing*, 3400-?
DUBUS Magazine USA Rep [hidden email]
======================================
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[Stu2-3]

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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[Colin VE3MSC]

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
>______________________________________________________________
>Elecraft mailing list
>Home: http://mailman.qth.net/mailman/listinfo/elecraft
>Help: http://mailman.qth.net/mmfaq.htm
>Post: mailto:[hidden email]
>
>This list hosted by: http://www.qsl.net
>Please help support this email list: http://www.qsl.net/donate.html

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