Manually fine tuning the TGXL

TMack409

This might be a fools errand on some bands with some antennas…. Hear me out… If you go to the trouble of super fine tuning (for the absolute lowest SWR) on a particular frequency (in my case 80M full wave sky loop on 15M FT8) and you notice that the tune bar is becoming excessively sensitive to knob (C1, L1, C2) movement - Back Out immediately and just use the autotune function. Because, otherwise, just a slight change in SWR (as your antenna "warms up") can bounce your finely tuned setting way out of kilter… causing your Linear (KPA500) to red light fault due to high SWR. Anybody else notice this??

David Decoons, wo2x

does your Sky Loop have a balun on it? Sounds like the balun is heating up.

TMack409

Yes, it has a 4:1 BD Hybrid balun.

David Decoons, wo2x

Sounds like the balun is heating up, causing change in SWR.

TMack409

The idea of balun "heating" kinda makes my point…. When the TGXL is "wound up tight" as when you are manually tuning down to the absolute lowest SWR (and the slightest movement of the knob jumps SWR up dramatically) it doesn't take much change in the characteristics of either the balun or the antenna wire itself to throw off the TGXL's settings.

John KB4DU

can someone explain to me why do this? The radio totally doesn’t care if the swr is 1.2 or 1.4. The feedline swr stays the same regardless of what the tuner does, so the feedline losses are always the same.

TMack409

This is an FT8 thing. Mostly to do with dialing in the ALC for lowest possible reading while striving to get max power out of your amplifier. It’s a fine line. Getting SWR to absolute min will keep you from chasing your tail re the ALC vs Power balance.

TMack409

@David Decoons, wo2x - I dug deeper… examining the balun’s connections more carefully. On the PL259 side of the 4116t balun, I use a UHF double male connector (HRO p/n UHF-10). The ground side surface of the connector has only two tiny “indexers”. They were both discolored from overheating - which told me they weren’t seated properly (which was preventing proper seating of the entire ground connecting surface area). Once the indexing tips were rotated a bit, so they could fall into the detent, the ground connection’s surface area was vastly increased. Apparently the threaded collar (of the adapter) wasn’t providing much of a ground path? So far so good. Thank you for putting me on the right track. -K4MPM