[hpsdr] strange SWR issues

[Ramakrishnan Muthukrishnan]

Hello HPSDR Hackers!

I have an Atlas based system with Munin2 and I have been happily using the system for a few years now.

Last week, I noticed high SWR with my 10m Moxon. And it also fluctuates a lot. I have an external tuner and it struggles to match the feeder+antenna. So, the values shown by the Alex coupler is also high since tuner has not matched. 

My first suspicion was of course the antenna, but antenna seem intact, I checked with a VNA and things look fine. I also changed the feeder with a brand new cable.

Here is the strange thing. If I bypass Alex and directly give the 100W PA output to the tuner, everything looks great. Power is going out, tuner shows a steady power output and SWR. Also, I used a 20W PA (PennyWhistle) with Alex and could make a QSO and got good reports, no issues with SWR. But if I use 100W + Alex Tx filters, I observe SWR fluctuations. I opened the hammond box that has the Alex filters, no burns or obvious failures. I also tried the "bypass" button on powersdr and still observe problems.

Now, my only suspicion is the relays and connectors in the path: K17, K18 and K8. The only variable I can now change is K5, I can try a different Antenna port, so K11/K14 (ant2 and ant3) is used.

Schematic here for handy reference: <http://openhpsdr.org/support/Alexiares/ALEX-P1.1.4-TX%20Sch.pdf>

Anyone else faced similar issues? I have also tried various patch cables etc just to rule out the cables in the path... Pretty much exhausted all possibilities now. Interesting problem and a lot of new learning, so amateur radio's purpose of self learning is served!

73
-- 
  Ram VU2JXN