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Re: [TowerTalk] Wireman Balun kits

To: "Tower Talk List" <>
Subject: Re: [TowerTalk] Wireman Balun kits
From: "Jim Brown" <>
Date: Thu, 06 Mar 2008 10:16:01 -0800
List-post: <">>
On Thu, 06 Mar 2008 05:53:10 -0500, Roger (K8RI) wrote:

>That's precipitation static, be 
>it rain or snow and it is a differential DC voltage that  creates 
>tremendous noise. 

It may start out as a DC voltage, but the CURRENT is RF -- the transient of 
the arc -- that's why we hear it. We don't hear DC. 

>but using a boradband transformer will turn that DC into a common mode 
>voltage that will lessen the noise noticeably. 

I suspect a different mechanism. Virtually all ham antennas are unbalanced 
by their surroundings, so unless there is a serious common mode choke at the 
feedpoint, there will be common mode current from any field that excites the 
antenna, including that static. If I'm right, a serious choke at the 
feedpoint would kill that part of it. If it's a differential signal, nothing 
is going to kill it, certainly not a transformer (voltage balun). 

Another VERY important point. Voltage baluns (transformers) put all of the 
transmitted power in the core of the ferrite. If you're running much power, 
that's going to heat the ferrite. If you're running enough power, it will 
saturate the ferrite and cause DISTORTION. That means harmonics and 
splatter. Current chokes do NOT see the transmitted power, only the 
unbalanced voltage/current, and if they have a sufficiently high choking 
impedance, they reduce the current (and their dissipation) to a very low 

>Nearby lightning strikes and direct hits are an entirely different 
>matter.  Installing large  chokes (linear or toroid) at the antennas is 
>not a satisfactory option  mechanically, 

Why not? It certainly is the best place to put one electrically for noise 
suppression! The coils of coax on toroids I've described can very easily go 
up at the antenna feedpoint. So far, I've presented my work to the guys at 
NCCC, NCDXA, REDXA, and PVRC. I've had many reports that their antennas are 
much quieter. 

>but is back by the remote switches which is where  I plan on using them. 

There's certainly nothing wrong about using a choke there, but it will be 
far more effective at the antenna feedpoint (that is, up in the air), 
because the length of coax between the feedpoint and the choke will act as 
part of the antenna. 

>The choke at the antenna 
>serves one purpose, but doesn't do much to mitigate lightning when there 
>are long runs of coax from the choke to the tower in which induced 
>currents can be substantial.  The chokes back in front of the remote 
>switches and grounding the coax shield to the tower can make a 
>substantial reduction in the lightning effects/damage.  

Wherever a choke is located, it will act as a very low Q parallel resonant 
circuit in series with the COMMON MODE circuit (and a short at DC). If it 
sees significant energy from lightning, there will be heating. If it sees 
enough, there will be melting of the coax and cracking of the ferrite. :) 
But for non-destructive amounts of energy, it will simply reduce the current 
(and may divert most of it to a different path by Ohm's law). 

>Another reason for the extra protection is I do not have the option of 
>disconnecting any of the rigs or even computer networks unless I have 
>plenty of warning. Doing so is a major undertaking as is reconnecting 
>them.  Just the computers can take up to  an hour to get back up and 
>running on the CAT5e network.

As you have noted, disconnecting antennas does NOT provide lightning 
protection. And several engineer friends who work in pro audio but have no 
antennas have lost computer networking gear to lightning strikes. It's 
voltage/current induced on the computer wiring, and voltage/current induced 
on power wiring, and the differences between them. 


Jim Brown K9YC


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