[TenTec] Open wire

[Robert & Linda McGraw K4TAX]

Excellent reply Stuart.

73
Bob, K4TAX

----- Original Message -----
From: "Stuart Rohre" <rohre@arlut.utexas.edu>
To: <ghoffman@spacetech.com>; <n8coo@juno.com>
Cc: <n4lq@iglou.com>; <TenTec@contesting.com>
Sent: Friday, October 18, 2002 2:16 PM
Subject: Re: [TenTec] Open wire


> If the feeders are truly balanced, and narrow spaced for the frequency in
> use, such as window line 450 ohm nominal and 300 ohm nominal at HF bands,
> there should be minimal field outside the feeders due to the equal and
> opposite currents principle.
>
> A well designed rig, installed properly, will not have RF in the shack.
> This means use of a well balanced tuner, and earthing measures that avoid
> having the distance to earth as a quarter wave of the band in use or odd
> multiples.
> This is where many have trouble, especially with unbalanced antennas.
>
> Use of true balanced antennas minimizes problems of RF in the shack, from
> both coax and balanced feeders.  (The coax feed using a balun at antenna.)
>
> That being said, if a particular rig has sensitive digital logic, modern
EMC
> methods of beads and choke cores on cables, improved bypassing, twisting
> power supply conductors and shielding them, all will help remove the RFI
> effects.
>
> Many hams persist in using off balance, off center fed antennas without
> balancing and thus will more easily introduce RF into the shack.
>
> Another method little known by hams, to mitigate RF in the shack involves
> running the coax feeder through a conduit, (the waveguide beyond cutoff
type
> of filter).  This affords certain off center fed verticals little to no RF
> on the coax outer shield.  It is a method easily implemented for a single
> problem band, although ferrite cable chokes may be easier to implement for
> multiple problems.
> 73,
> Stuart K5KVH
>
>
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