For quite some time now we’ve had an issue with our SteppIR vertical antenna. It works great on 40 meters and above, but darn if it gives us high SWR on anything below 40 meters. What is strange is that when power is low (I mean less than 10 watts), all is well. Get above 10 watts, and SWR goes up to 3:1. This project has been tackled by TJ Sheffield (KL7TS) and he has been wrestling with it for a while. He’s inspected, cleaned, replaced the 80-meter loading coil, disassembled, reassembled, and gotten many headaches along the way. Here is his report from yesterday’s efforts, although somewhat edited in case children are watching! ……
Thursday was another day and another session with the vertical.
I stripped off the coil, the wind reinforcing kit and opened up the motor drive housing.
I had this idea that the “copper crumbs” I saw on the SO-239 might be a high voltage path on 80m
and 60m, when the coil is in the system and provides a crummy (get it?) path that shorts RF to ground.
My theory is there is high voltage present when using the base loaded coil, but when the vertical is on 40m it is a “full size” (i.e. quarter wave) Marconi vertical and the feed point sees high current, but low voltage, and that’s why it works on 40m (low voltage) but not on 80m or 60m (high voltage).
I brought down the Honda 02 generator this time. It took 13 pulls on the starter rope to get it going, but it started.
I filled up both generators with Chevron gasoline and STA-BIL, right up to the filler cap. My theory is if the fuel system is full right up to the brim, there is no air available to interact with the fuel system and gum things up. What do you think?
I brought the air compressor down to blow out the crumbs. I used an old N95 mask and stood upwind, then blew out the housing and especially the “platen” where the copper tape feeds through the RF contact brushes. I shot in some contact cleaner under the platen, and on the SO-239 connector, and washed (and blew) the crumbs away — rinse and repeat!
I buttoned up the motor housing, re-installed the wind reinforcing kit and connected up the coil.
I put 10 watts to the vertical on 80m and SUCCESS — the SWR was 1.4 to 1 and holding steady. I increased the power to 100 watts and the SUCCESS continued. I tried 100 watts on 60m and had SUCCESS there as well.
I really thought I had this thing cured, until I put the ACOM amp on it — FAILURE.
I had dialed up 1,400 watts on the dummy load, then changed to the vertical and the ACOM amp immediately went into fault. I checked the SWR using 40 watts and it was back to 3:1 again, so FAILURE.
But I think I’m on the right track. The motor drive “platen” (brush contacts) are suspect now. I don’t
think I’ll fool around with trying to bench repair this unit, I’ll see if SteppIR will take it back for a “core charge” towards a new motor and tape.
Tomorrow is Friday, they might close early for the 4th. A fifth is a pretty good choice for celebrating, too!
TJ Sheffield, KL7TS