I’m trapped (and some LZDX contest too)

Having been a teenager in a good part of the eighties, some of the pop classics of that era stick around. One of those catchy tunes is Trapped by Colonel Abrams. I felt trapped for half of this weekend. Yes, sometimes a ham gets trapped by… traps!

Two weeks ago I put the Fritzel vertical back up to have a SO2R antenna on the higher bands in the coming contests. It’s a simple trap vertical, and I made a set of three resonating radials. The whole thing is up about 5m in the air. For its simplicity, it is a winner. I checked the curves on the analyzer and the SWR dips were clearly there. Friday I was setting up for this weekend’s LZDX contest and checked the vertical on the second K3. It was good on 10 and 20 but SWR showed 3.6:1 on 15. Say what???

This isn’t a disaster as it’s only my second antenna. Still I want it to work. So Saturday morning at 09.00 local, I tackled the problem. Loosen radials from bushes, tilt over pole, loosen screws and take the trap. A Fritzel trap is made of two coils in a big tube which acts as a capacitor. How do I know? I have a toasted trap! One half clearly had a problem: there was dirt on the coil, probably brought in by insects. The lower half of the trap is open so that there can’t be any water build up. However there was moisture in there too, probably from condensation. It was freezing at night and in the morning the sun was shining so this combination makes for a wet environment. Probably exactly this combination of circumstances that made the WARC trap blow last year.

Cleaning the trap took half a minute, while  singing the Colonel Abrams song “Oh no I’m trapped, like a fool locked in a cage”  but I wanted to make sure the other half of the trap was clean. Opening this made the sealing cap break. I knew a frozen plastic is brittle so I took it to my work bench and warmed it up with the heat gun. Nevertheless it broke @{#{@#|{|@ so I had to seal it afterwards. Tek7 anyone?

The upper half was very dry and clean so I should have left it but better safe then sorry. Put the thing back together, hang radials in the trees again, check resonance and bingo! It resonated right where I wanted it.  Back to the shack. WTF? SWR still 3.6:1? Oh no I’m trapped! Let me see. It can’t be the K3 or the band pass filters: it works on the yagi. Coax cable? Then why are 10 and 20 ok? Must be something else then. Darn traps. That antenna has to go, period.

Then the contest started and I used the vertical intensely to practice my SO2R skills for next week. I ran on ten meters and worked all I heard on 15m. The high SWR made the power fold back to 50W or so but in CW that’s about the same as 100W. About the contest: I made 1000 QSO in 10 hours so the rate was OK in the first half. Then the rate dropped and I was tired. It was 2200 utc and I took a break. Nature called and I took the time to rethink the trapped situation. There was one little thing I had excluded from my investigations. Namely: the antenna switching matrix in the band decoder. I did not consider that because I was confident it was good. Why else would 10 and 20 be good? Why would I take a different port for 15 than for 10 and 20?

But one thing I have learned in all my years in electronics and trouble shooting: never exclude the obvious from your check list. I was ignoring my own principles here. So back to the shack, open the device configurator and look at the antenna switching matrix. Sure enough: the second antenna for 15m on the second radio was routed to the wrong port. In fact I had been using the 80m GP on fifteen meters with an 3:6:1 SWR.

Changing the checkbox and uploading the values to the decoder solved the problem. SWR now 1.4:1 on 15. “Like a fool locked in a cage…” Why on earth did I check the wrong antenna port? “I can’t get out you see I’m trapped” It’s only now, as I type this, that I remember: I used this port for the 15m Moxon I made in March for WPX SSB.

This morning the antenna was shining on 15m. With 100W I could work deep into UA9 and log DX while running on another band. I must admit: it hears better than the 80m GP  🙂

Lesson (re)learned: always obey your own laws and follow your principles. Even the obvious might fool you!