[Elecraft] New P3 TX Monitor....unusual behavior with SWR (at times)

[Jessie Oberreuter]

      I had a similar problem -- even at low power levels, the W2 would 
periodically spike a high-SWR and even show 2-3 bars of SWR when no signal 
was present.  I swapped out the 8-pin cable connecting the sensor to the 
W2 and the problem went away.  I re-crimped the connectors on the original 
cable, but haven't yet swapped it back in to see if doing so fixed the 
problem.

On Wed, 12 Aug 2015, Randy Farmer wrote:

> I find this thread quite interesting. I too have been dealing with VSWR 
> "spurts". My TX lineup is similar to Phil's, but I don't have the TX 
> Monitor. After a recent station rewiring job I found I was having a 
> great deal of trouble with indicated VSWR jumping to high levels with 
> the amplifier on. The problem was especially bad on 80 meters -- 
> anything above about 300W would randomly give a high VSWR fault on the 
> KAT500. Since the KPA500 was feeding the suddenly changed load it too 
> would usually fault out. The sensor for my LP-100A is on the antenna 
> side of the KAT500, and its VSWR indication was rock solid during these 
> events. My station is in an extremely difficult RFI environment, with 
> seven antennas crammed onto a 0.2 acre city lot. I immediately suspected 
> that common mode RF was getting into the reverse power sensor circuit in 
> the KAT500.
>
> I installed a Balun Designs choke on the antenna side of the LP-100A 
> sensor and the KAT500 stopped giving the high VSWR indications right 
> away. That's the good news. The bad news is that now the KPA500 is doing 
> it, but at considerably higher power levels. I can run around 400W out 
> before the KPA500 begins to randomly show VSWR faults. The KAT500 is 
> completely stable at full power. For now, I'm living with this situation.
>
> So I would suggest the troubles you're seeing may be the result of 
> common mode RF problems on the transmitter feedline. It could be that 
> the addition of the extra electrical length of the TX Monitor sensor and 
> its associated cabling changed things just enough to put a common mode 
> voltage node near the KAT500 output port. You might try adding an 
> additional piece of coax somewhere in the lineup and see if that changes 
> the situation. RF is funny stuff.
>
> 73...
> Randy, W8FN
>
> On 8/12/2015 10:10 AM, Phil Hystad wrote:
>> Mike,
>>
>> Thanks for the comment.  I only have one K3 with one P3.  My configuration 
> is:
>>
>>       K3/P3 —>  KPA500 —> TX Mon Sensor —> LP100A Sensor —> KAT500 —> 
> 80-meter Dipole
>>
>> I first noticed the spike with the RED LEDs on both the KAT500 and the 
> KPA500.  I was not looking
>> at the SWR display on the P3 although the second time I did notice that it 
> too spiked (max reading).
>>
>> Like I said, I was operating CW and when I sent just the first dit of a QNI 
> into a CW net the spike occurred.
>> I stopped, and then keyed again and everything was normal.  The second time 
> that I did this, I thought that
>> maybe the spike was momentary and continued keying but the second or third 
> key down action (actually, a paddle)
>> resulted in fault with the KPA500.
>>
>> Last night, I did not have any problems at all because I disconnected the 
> TX Mon sensor.  I will continue
>> experimenting though as I don’t have too many data points yet to draw 
> conclusions.
>>
>> 73, phil, K7PEH
>>
>>
>>
>>
>>> On Aug 12, 2015, at 7:28 AM, Mike VE3YF <Mike at ve3yf.com> wrote:
>>>
>>> Phil:
>>>
>>> I have the same setup but only 1 x P3. A K3 and P3 on my left setup and a 
> K3 on the right setup using a MK2R+ and I noticed what you mention only once. 
> I was on 80m with
>>> the Right K3 and I saw a brief Power and SWR spike on the Left P3 and K3. 
> I might have had a bit of SWR on the standalone Right K3. I have not noticed 
> it happen since, it might
>>> be a band/swr specific issue ie, as I was operating around 3800 and the 
> antenna is designed for the CW and RTTY portion of the band. The Left side 
> radio was on 160m Sloper
>>>
>>>
>>>
>>>
>>> 73 De Mike
>>> VE3YF
>>>
>>> http://www.ve3yf.com
>
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