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 <kl...@acsalaska.net> To: Elecraft@mailman.qth.net 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 <s...@stu2.net> Subject: [Elecraft] XV432 Oscillates with Amp connected To: elecraft@mailman.qth.net Message-ID: <4dc6d43f.2090...@stu2.net> 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 dubus...@hotmail.com ====================================== ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
