During WAE SSB contest (9th and 10th Sept 17) while giving WTC, I noticed that suddenly otherwise all good SWR shoot up and drowned the signal putting my amp on alarm mode. Went to terrace to check all the antenna parts and coax joints etc. I have a Spider beam and a 40 meter vertical connected with separate Coaxes coming down to shack where they end up in the Antenna Switch, then to Directional Coupler for my SWR/Power Meter, then to LDMOS Amplifier and finally to TS590.
I found that small drops of water inside of the spiderbeam antenna coax joint. Shook that part to drain any drops out of the joint and then put insulation tape again on top. Back to shack, it did not seem to improve the SWR. Even with Amplifier on bypass mode, i could see SWR going over 9 on power meter.
I suspected that the homebrewed Balun box at antenna feedpoint getting flooded due to rains. I didn't had any drain holes made to them to take care of such situation. This means, i had to lower the spider beam which is a cumbersome task for me..
Many of my friends VU2PTT, VU2IBI, VU2DED, VU3NXI and others provided some very good tips including how to check Coax separately, Checking the connector etc. I thought i checked everything.
Couple of days later, i just connected Coax coming to shack directly to the rig, bypassing all other jumpers, power meter, power amp etc. I could see SWR as expected less than 1.5. wow!. When I connected back to Antenna switch, again SWR shoot up.. So now it seems i have cornered the problem.
But then, that evening again i started some more test. I connected coax directly to TS590 and started given 100W for few seconds. I could see that SWR raising from 1.2, 1.3-1.5 , 1.7-1.9 and then 2.5 and i stopped. This indicated that my problem is not so easy to solve.
I then went for Time Domain Reflectometry (TDR) with VNA to see if i can detect anomalies in the Transmission line. Following images show the patterns i observed. First one is for line running to 40mtr vertical (it has LMR 400 25 mtr and 15 mtr lengths), second one is for line running to spiderbeam (it has RG213 25 mtr and 10 mtr lengths) and last one is brand new 15mtr length quality 213 rolled in my shack with one open end.
I could make that on RG213 line running upto the coax junction, there is no reflections and segment is holding good on pattern. It indicates to me that, line is clear of any water content. Then i went and checked the barrel joint to find a sticky type of material on center pins. So, replaced the barrel connector with the new spare one i had to find that the Spiderbeam is now giving the expected results!.
On the Vertical antenna path, i noticed that the crimped connector on LMR400 is freely rotating giving up ground connection. This requires replacement of my coax till i get a new crimp done.
So this troubleshooting continues...!
Enjoy
73
Kiran
