Weird Behavior on 80M

Russ Ravella · January 2023

I'm trying out a new upgraded 80M coil for my SteppIR BigIR vertical. At 3570 its SWR measures about 1.4:1 with my analyzer. My Telepost LP-100a and LP-500 both show the same. The TGXL (bypassed) and PGXL show the same as well. If I un-bypass the TGXL and hit "Tune" it shows it gets to about 1.2:1. However if I actually transmit though it, it suddenly shows 1.82:1 ! I hit "Tune" again, it shows 1.2:1 again, then I transmit and get 1.82:1 again. Weirdly, even though the TGXL is reading 1:82:1, the PGXL behind it still reads about 1:4:1, the "native" SWR of the antenna on the other side of the TGXL, which as I said is showing 1:82:1.

Why would the TGXL tune to 1.2:1 but actually provide 1.82:1 in actual use ? Has anybody else seen this ?

Thanks! Russ KR6W

Alan · January 2023

Russ

I have the same configuration.

You mention using a PG-XL. What is your power when you TX and see the higher SWR?

In my case, two times, the higher power TX was causing an arch over on the 80M coil rotary switch. No arch over when "Tune" because there is no arch over.

If this is the case, open the coil and remove the arch trail before you cause more significant damage to the rotary switch board (ask how I know this).

Alan. WA9WUD

Russ Ravella · January 2023

Hi Alan,

Thanks very much for your reply. I think you've got it exactly. After posting this, I noticed I'd inadvertently done something (long story) that caused the EHU control cable to lay along side and touch the coil HV cable. When I eventually raised power to around 400W, ****, I arced the coil ! I'm going to open it up today to inspect the damage but I expect the worst.

I was wondering if the proximity of the cables might have been causing this weird behavior at lower powers and your post just confirmed the reasonableness of that guess. As soon as I get the coil back on its feet (probably by replacing it - alas ...), I can test the theory.

Thanks for taking the time to respond Alan ! 73 Russ KR6W

Alan · January 2023

"....if the proximity of the cables might have been causing this weird behavior...."

Yes, done that to.

The 80m coil control wire has a shield, which should be grounded.

I had on occurrence where the control wire shield provided a path from the antenna wire to ground. The resultant arch destroyed my 80M coil housing.

80M, even moderate SWR, and high power equals very high voltages.

Alan

Russ Ravella · January 2023

Very true. Fortunately, SteppIR recognizes the original 80M coil design isn't as robust as it needs to be. When I bought mine, they advertised it as being rated for 1500W and when I called them and asked if that meant "all Ham modes for normal tx times", they said yes. And it might BE for "perfect" installations. But mine isn't and I've blown THREE coils by just trying to run above 1K. They've repaired them each time without charge but it's still a hassle for both of us.

The last time, they asked if I'd like to try their new prototype ruggedized board design and of course I said yes. But I blew the first one of those up too. They've had a further redesign since and now I have that one - again, all at no charge to me (very impressive).

The issue I reported here of course is TOTALLY my fault and no indication of anything other than my own stupidity. Since my last post I've opened the coil up and it actually appears completely unharmed ! I can't explain it but I'm definitely relieved. I've carefully rerouted the wires now and retested it and it works perfectly at the power it blew before when it didn't when I tried it again right after the disaster. I guess it "cools down" or something ? Anyway, it proves your theory because the tuner works perfectly now.

I'm not going to try the coil at anything over 1K until after the Bouvet DXPedition is over just in case (yeah, it's crazy to think I could get them on 80M with a vertical from S. AZ but I'm going to try). Anyway, thanks again for your posts - very helpful! Russ KR6W

Weird Behavior on 80M

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