1:0 Balun

Severe storms and winds this weekend prompted me to take down one of my two antennas for safety.

I have a 20m inverted-V dipole with 1/4 wave 300Ω twinlead as the feedline from the center insulator to a 1:1 current balun mounted on my wall (the twinlead is transparent at 20m frequencies). The other antenna is a 20m “hamstick” style vertical dipole with RG-8x feedline; this is the one I took down.

Lately, I’ve been having a hell of a time getting anything to match on 40m with my tuner; usually my inverted-V can handle it since 1/4 of the 40m wave is on the twinlead (at reduced effective radiating power, of course), but for as long as a few weeks, it’s just been a shit of an antenna, even on 20m. So my vertical has been my workhorse.

Well, I’ve been having a lot of 40m noise lately at my apartment, and I wondered if it’s because I don’t actually have any 40m resonant gear in the air. So I looked into getting a pair of 40m hamsticks assembled to replace the 20m hamsticks. While kind of randomly checking out my gear (because I was curious how my inverted-V was doing), I put my analyzer on the inverted-V coax and got some seriously strange readings.

Tested the RG-8x feedline with a 50Ω calibrated dummy load, and got 50Ω-ish back. Took two 100Ω resistors in parallel (for 50Ω) and placed them across the 1:1 balun terminals and got 500Ω across many bands. WTF. Pulled it down and shook it; heard a rattle inside. Well, damn.

With the storms, I was worried that it got an induced shock from lightning and fractured the iron core; thankfully, that wasn’t the case. What is the cause is physical stress, thanks to my stupid design of the 1:1 balun. While tightening down the red banana terminal of the pair, I twisted the entire assembly until the wire between the inductor and the terminal snapped. So all this time I’ve been operating that inverted-V with one lead.

1:1 balun with snapped wire on red terminal.

No fucking wonder I’m getting so much RF back into the shack. I and my gear are the counterpoise. And still nobody hears me.

I picked up some banana terminal blocks at the Schertz Ham Fest last year and noticed that there’s an industry-standard spacing on banana terminals: 3/4″. I made this 1:1 balun (and my 4:1 also) at 1″. That just won’t do. So I have to re-drill the cases to accommodate the terminal blocks so I can put actual male banana terminals on my twinlead line so I don’t have to twist anything anymore.

Radio is hard. And I just don’t know why I’m making it harder.

Published by Shawn

He's just this guy, you know?

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