RF TX mismatch

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  • Updated 1 year ago
I recently replied to a posting about multiple crashes during the WPX RTTY contest. I had no crashes during the contest but I did have one right after. It happened when I accidentally transmitted (60-70 watts) into my tuner which was set to the wrong band. What happened was the 6600 locked up and SSDR shut down leaving the radio in transmit mode -Red light on. After a bit the radio reset. 

Someone also posted to this topic and said (in part) this:
 This acts like a RF TX mistmatch. The radio will fault into a red flash then reboot when this     happens.

I read the error codes section in the manual and it does not mention this error condition. 
Is it normal for this to happen if one transmits into a high SWR? Seems like the radio should just reduce its power and not shut down.
I'm asking this because about a month ago I had a rash of this type of shutdown. I tore the station all apart trying to resolve the issue but it seems to have gone away. I would like to know if this type of crash can be caused by transmitting into high SWR. It might help me if the problem returns.

Mark K5XH

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Posted 1 year ago

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Photo of Joe N3HEE


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I think its unlikely the radio will crash on high SWR.  I've accidentally transmitted into high swr on many occasions with no issues.  The radio just folded back the power output.  I suspect you guys are experiencing some RF getting back into the radio.  That may cause the radio to crash.  When you rebuilt your station perhaps you fixed your issue without realizing it.  A loose coax connector or ground connection or placement or routing of wires is all it takes.  I use ferrite cores on interstation cabling and ferrite chokes on all feedlines at three different places.  One at the antenna, one at my entrance panel (which is also grounded)  and one at my antenna switch in the shack. 
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N5LB - Lionel B

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Months ago I had a problem with my 6400 crashing and the power switch flashing red.  Figured it was RFI, I put in lots of ferrite, rerouted the ethernet cable, replaced my ethernet card, changed (and improved?) station grounding.  I pulled all RG8X and put in LMR400 jumpers.  Still crashed.

Here was the problem.  I had an Alpha Delta antenna switch between the outboard auto tuner and the antenna-bad practice-I am going to say it was inadvertent (hmmm).  Apparently under certain conditions, most of the time for me, the Alpha gas discharge tube would fire (low voltage tube) effectively shorting the feeder.  Wow, this event really upset the 6400.  Viola, moved the switch to between the tuner and radio and all was then fine. Been fine ever since.

I guess my point is that the cause of a crash can be tricky to find and, at least in my case, was hiding in plain sight.  RF is sneaky.

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Thanks for the replies. I am pretty sure it has something to do with RF getting into something. I have chokes on everything and everything is grounded to a common copper bar. I unhooked all the unnecessary stuff (key, speakers, etc) and could still trip off the radio while transmitting into a dummy load. I even moved the dummy load out into the yard on 100' of 9913 coax. So the problem seems to be in the shack.
Lionel's experience seems to be what is happening to me - but I don't have any gas discharge devices. My problem always happens at the very start of a transmission, never during a transmission. And it is not consistent. Sometimes I cannot duplicate the problem. Oh well, the hunt will continue.
73, Mark K5XH 

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Pat - WH6HI

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Your ground is not as viable as you may think. You have hooked every thing up correctly, but how long is the ground run to earth ground. Wave length as it relates to your ground run is important. If your run is at quarter wave length or smthing close at the frequencies you were having problems on. Then you need to reengineer the ground to eliminate the voltages being seen at the station ground. This is something you need to look at. Wavelength of the ground is often overlooked.