PGXL: Low SWR on CW. High SWR on USB. Same Ant, Freq and Drive power!

KM6XX

PGXL with 3.4.10 driven by a 6600 running SSDR 3.1.11. At the same frequency (~14.202) and same drive power (~46W) I get ~1200
https://www.youtube.com/watch?v=3kpf6H3ZUWk
W and a 1.5:1 SWR with a CW tone. However, using USB I get a "HIGH SWR RFP" warning in the PGXL utility.  This is new.  I've never seen this issue before. See the attached video.  Any ideas?

Sergey KN7K

Can you check on dummy load?
IS it possible something changed at your antenna? What antenna do you use?
I run PGXL on few bands, SSB tested only on 160 and 40m and so far all good.
Sergey, KN7K

KM6XX

Sergey-  

Thanks for the suggestion. Yes, I just did, and the issue does not happen on a dummy load.  

I haven't changed the antenna at all and after inspecting it, I don't see anything obvious.   I just rechecked the SWR with the SWRPlotter program from K9DUR and the SWR is virtually unchanged.  

The antenna is an 80m 1/2 wave end fed, with a DAVIS RF common mode choke near the feed point.  The coax is Times Microwave RG214. As another experiment added 6 snap on CM chokes to the coax, just outside the shack.  Unfortunately the problem persists.  

What stumps me is that less than a week ago I was using the PGXL with no issues.

DL4RCE

Please read the changes of the update to the PGXL software, there is an update also to SWR related / protection stuff. 73 Volker

Al K0VM

If you reduce power in SSB to say half power, does it still happen ?   Possibly something arching at high RF.

AL, K0VM

DL4RCE

"Fast SWR Protection: The Power Genius XL hardware protection system, designed to prevent damage due to high SWR events, is now more sensitive and reacts faster."

Dan-N7HQ

The High SWR (RFP) alarm is telling. 

There are two independent, directional coupler circuits in the PGXL.  One, serviced by the primary microprocessor, monitors power and return loss between the antenna and the amplifier.  The second, by an (RF Protection) RFP microprocessor, monitors from the PA MOSFET perspective.  This design allows the PGXL to protect the PA against failures in components, internal to the amplifier, but external to the finals. 

Prior to v3.4.10, the RFP, by default, calculates SWR using a firmware algorithm.  If the RFP detects a high SWR condition, it 'trips' the alarm within about 1 millisecond.   However, the hardware in the RFP circuit employs an analog IC that can respond to high-SWR conditions within just a few microseconds.  This adds several orders of magnitude faster protection; and a feature not the norm for Amateur class amplifiers. 

We enabled this feature as the default in v3.4.10.

Why? 

Early, during the alpha stage, this feature made it difficult to understand if a specific problem was caused by an antenna system issue or something in the amplifier.  As the number of amplifiers in use by customers increased, our data, understanding/confidence in the accuracy of this super-fast protection increased. 

As Al, suggests your alarm may be the result of a transient caused by a component/condition in your antenna system that is struggling at high power.  I experienced this issue when moisture found its way into a dipole balun.

Here are the steps to a resolution: 

1) Please do this first. Check your antenna system - this covers the vast majority of issues. Especially when the problem is not reproducible on a dummy load.  Note that running an SWR test with <insert rig here>, or an analyzer/VNA is not adequate. The tests need to be at power. 

2) Create a helpdesk ticket and schedule a call and team viewer session with our team - they can run some tests that will isolate or fix. Again, once the antenna system is cleared as the cause.

73,

Dan, N7HQ

Sergey KN7K

Hi Dan,
I discovered one issue yesterday during 7QP contest.
During TX, by accident I touched VFO on Maestro and frequency slightly changed, immediately I got "High SWR RFP" error.
I reproduced it several times.
I know it is not desirable to touch VFO during TX, but I wonder what is the mechanism to to enable this message during such events?
It is nothing to do with antenna.

Here is a brief demonstration
https://drive.google.com/open?id=17BkBJVzSppH_ednZCBFrNKdHs25a5KrR

Thanks
Sergey, KN7K

Tim - W4TME

Cabral, please open a HelPDesk ticket for your issue are suggested by Dan so we can address this issue for you.

KM6XX

Dan-
Thanks for the detailed explanation.  I believe you are correct in the issue is related to the antenna system.  I did a battery of tests on my feed line system with a dummy load to rule out possible issues with the 8" coupler penetrating the wall of my shack, the Davis CMC and various feed line sections that make up the antenna system.  All of these components tested out fine under high power. 

However, having the manifest itself during USB transmissions and not during  constant CW transmission had me believe it was  RF in the shack.   

Do you have any data that suggests the directional couplers are susceptible to wide band RF current vs narrow band?

Also, I have a AM radio tower about a mile from my shack and the signals at 780kHz are outrageously high. Do you know of the directional couplers are susceptible to external RF?


That being said, I changed my antenna feed system based on a paper on End Fed Half Wave antennas to reduce the likely hood of stray RF in the shack. It recommends a  0.05 Lamda  length of coax from the feed point to the CMC.  I found some interesting results:
1. With a 14ft length of coax (0.05Lamda) between the system passed! Please note the SVSWR was 1.36:1.
2.  If I reduce the length by about 3ft, the unit systems fails with "High SWR RFP".  The SVSWR was 1.26:1.
3. Reducing the length further reduces the SVSWR and the system fails.

This begs the question, Why would the lower SVSWR lengths fail if the there is less reflected power?

I don't believe it is moisture, as I live in Arizona and it is very warm and dry right now.

I'll do the help desk ticket right away.

KM6XX

Will do Tim.

KM6XX

My Ticket : Request #36978