[TowerTalk] Fair rite materials for choke baluns

[Earl Morse]

Had to look at a Windom, couldn't remember exactly what it was.  I knew somebody would have a single antenna that did DC to daylight and need to match it to their rig.  I am fortunate now and have at least one if not two antennas on each band so I don't have to compromise as much.

We are actually talking about two different things.  The Windom looks like it uses part of the feed line as part of the antenna so needs a brute force choke to decouple the feedline and keep that part of the feedline as part of the antenna instead of bringing it into the shack.  It doesn't look like that choke does any of the impedance transformation or balanced to unbalanced transformation that a transmission line tranformer (balun) does except through brute force choking on the coax shield.  So it would need only have enough inductance to isolate and not so many turns that it goes resonant before getting above the range of frequencies at which you use the antenna. If the choke works at your lowest frequency it will have even more impedance at the higher frequencies until it hits self resonance.

The transmission line transformer (balun/unun) can very efficiently isolate, transform impedance, and tranform from balanced to unbalance within a limitation of impedance ranges and frequency ranges while the choke operates as an inductor having impedance until it hits the self resonant frequency (inductive reactance of coil equals the inter-turn capacitive reactance) so it essentially decouples the rest of the feed line from the antenna.  I would say that the Windom antenna starts at the choke and not at the center insulator.

Balun probably is the most misused word in ham radio, it has come to mean almost any bump on the line between the transmitter and antenna regardless of whether it is a choke, balun, unun, transmission line tranformer, length of feedline, insulator, etc.  I know I am guilty of interchanging balun and unun all the time, its just that balanced to unbalanced transmission line transformer is so long to say and type.

Earl 
N8SS


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Message: 4
Date: Mon, 4 Jul 2016 19:26:52 -0400
From: Hans Hammarquist <hanslg at aol.com>
To: towertalk at contesting.com
Subject: [TowerTalk] Fwd:  Fair rite materials for choke baluns
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I have to answer you here, Earl:" I'm using a Windom/Longwire antenna. I can tune that to 160m - 10m easy. I can even load it up on 6m although I'm still waiting for a QSO there."


As I am "balancing" my feed line, or more correctly, am reducing the RF in my shack by putting a choke between the tuner and the radio (the "output" that is the end facing the TRX is well grounded for further reduction of RF in the shack) I am depending on maximum available Z in the choke all the way from 1.8 MHz to 29.7 MHz.


I am presently relying on a choke made of 50 feet of RG58 wound on a 4 inch PVC pipe. I am using a variable pits to avoid a specific resonance and thereby achieving a reasonably wideband, high Z. The choke is about 12 inch long.


Hans - N2JFS