Very high Intermittent SWR on TS950 SDX!!

JJ2013 · Post by **JJ2013** » Mon Aug 11, 2014 3:04 pm

Hi y'all!!

This isn't directly an audio question, but I am hoping that someone can provide some advice on this!

I will need to study this further, but through the process of elimination I have determined that as soon as I switch the linear amp on, the SWR meter shows a high SWR (just north of 3:1) although this lasts for perhaps 100ms only! Let me qualify this by saying that obviously powering up the linear is not what I am talking about but rather when I go from STBY to OPERATE position is when this SWR peak takes place.......

I think I will need to also take a look at the coax connectors on the chassis of the AMP itself as it seemed like one of them appeared to be "loose."

To recap,when the AMP is powered up but it is on STBY I have no SWR issue at all and it appears to be 1:1! Using an Ameritron AL-811H and also the Buffer relay ARB-704 between AMP and 950SDX.

Sure would appreciate some comments and advice!

Cheers!

JJ

UPDATE as of Aug 12:

Murphy is clearly at work here.......When I did some testing on the 15 m band with the AMP on, there was no issue at all. However, on both 14 MHz an 28 MHz, I see those very short-duration spikes of high SWR and from a wavelength perspective it is interesting to note the harmonic relationship...... Perhaps I try using different length jumpers or coax? That would be the easy fix.........

Note I have 8 snap-on ferrites on the coax at the entry point to the house and I have 7 snap-ons ferrites at the feed-point of the antenna with the appropriate mix. I have found that they do make a difference.

I also tried reducing the drive from the exciter dramatically to put out only 150 W from the AMP and the spikes could be observed with the AMP on, but after I threw the big switch on the AMP to STBY and used just my exciter to put out the same 150 W there was again no spike! I didn't repeat this experiment on the 15 m band or 10 m band....

Tried adding a longer run of coax but it did not make any difference (although I didn't run the experiment on 15m/10m bands!).

The saga continues

Post by **Voodoo Guru** » Tue Aug 19, 2014 1:03 am

Howdy JJ,

We've noticed that the SDX does have a little quirk in that it will show a SWR and ALC "spike" every now and then. This is just an occasional occurrence and does not happen every time.

We know of a few SDX operators that had similar SWR problems as you and found bad coax connectors or coax.

You might try another amplifier and see if the anomaly continues, you could have an issue with the input tuning of the amp which only comes inline when the amplifier goes to OPERATE mode.

Sounds like your on the right track though. Let us know the results of your search. It will be interesting to see how this plays out.

Take Care,

JJ2013 · Post by **JJ2013** » Thu Aug 21, 2014 7:15 pm

Hi y'all!

Guess what?? I opened up the AMP and found one dead tube and a second one that was acting up and looking pretty suspicious. I checked some of the resistors and diodes for good measure as well, but I was kind of thinking that as I never blew a fuse those diodes in the power supply block might be ok and they were.....

Don't see no spikes any more, but the meter does show minor SWR (like a couple of LED bars worth.....) now, but no spikey

Thanks for the comments incidentally!!

Cheers!

JJ

JJ2013 · Post by **JJ2013** » Sun Aug 24, 2014 2:47 pm

Hey VooDoo Guru!

After installing the set of 4 matched tubes that I received, I went on the air again and did enjoy "SWR spike free" operating for about 30 minutes after which the spikes reappeared! Perhaps this was just a fluke?

I also tried operating the 950SDX using a regular hand mic (just in case my audio rack would be picking up RF although it does have plenty of snap-on ferrites on INs/OUTs) but no difference! Even happens when transmitting into the Palstar dummy! My antenna coax also has heavy-duty ferrite snap-ons (7 at feed-point and 8 at entry point to shack).

Then I tried operating my IC756 Pro III on phone using the AMP but the meter on the Pro III does not show any spikes! Then, hoping that I had perhaps lucked out I then switched to the 950 SDX and also do not really see any SWR spikes although I did testing only for a few minutes (both in dummy and into antenna).......hmm......this is getting too intriguing

Note, I played around with the ALC pot on back of the AL-811H amp as well, perhaps THAT made the difference? Dunno! Will make some QSOs later tonight to see if the problem went away! Wouldn't that be great except that I would still not know what exactly the problem was?

Cheers!

JJ