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Re: [TenTec] RFI question for Orion and other TT rigs

To: "'Discussion of Ten-Tec Equipment'" <tentec@contesting.com>
Subject: Re: [TenTec] RFI question for Orion and other TT rigs
From: "Tommy Alderman" <aldermant@alltel.net>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Sun, 26 Jun 2005 14:20:08 -0400
List-post: <mailto:tentec@contesting.com>
I believe what you just said was this:


One of the best and easiest ways to avoid "RF in your shack" is to make
sure that one half the length of your antenna plus the total length of
your feed line is NOT an odd quarter wavelength long. The reason for
that is if that total is an odd quarter wavelength, you will have a
maximum voltage field in your shack. The second most easiest thing to
avoid is do not let the end of any of your antennas terminate directly
over your shack, as that too, is a high voltage field point.

Tommy - W4BQF"

-----Original Message-----
From: tentec-bounces@contesting.com
[mailto:tentec-bounces@contesting.com] On Behalf Of Robert & Linda
McGraw K4TAX
Sent: Saturday, June 25, 2005 9:42 PM
To: rsrocket1@comcast.net
Cc: Tentec
Subject: Re: [TenTec] RFI question for Orion and other TT rigs


Any rig is subject to RFI under certain conditions.  Some are more prone

than others while some fair better in random RF fields.  The general 
conditions which contribute to RFI issues are those rigs that have lots
inputs and outputs.  Inputs and outputs not only mike but key,
remote keypads, data ports, serial ports, external audio in's and out's,

power supply leads and etc. just to name a few.

Some of the rigs add bypass caps to the in's and out's and some add
beads or chokes.  In each of these applications, implementation of 
"filtering" does reduce the acceptable bandwidth of the port of concern.

Rolling off or reducing the high frequency response of a digital port or

data port will limit the upper limit to which data will pass.  High
data has sharp edges thus requiring wide bandwidth of the port.  This is
open invitation to RFI.  Audio lines, key lines and such are no

Grounding is always a question of concern.  In true practice today, most

antenna systems do not need a ground to properly radiate.  This includes

dipoles, beams, and center fed balanced antennas.  Those that require a 
ground are unbalanced wires, verticals, off center fed Windom's and
Today, most stations only need a safety ground or one supplied by the
pin of the AC mains service.  Any attempt to "ground" the station can
with problems which can actually make RFI worse.  Look at it this way, a

ground lead from the radio to a driven ground that is approximately 8 ft
length is approximately 1/4 wave, electrically, above ground.  That's
wave on 10M.  If the ground wire is some 17 ft then that is 1/4 wave on
In looking at a 1/4 wavelength, one will see that if one end is at zero
potential then the other end is at a maximum RF voltage point.  Yes the
is a DC ground but at a very high potential point with regard to RF.

A second point where RFI may occur is one where the radiating portion of
antenna is very close to the station.  One where a leg of a dipole runs
the house which then will produce a very high level of RF in the
position.  Here is a case where lead length, connections between radios,

tuners, computers, mikes, keys and keyers and such will serve as small 
antennas and thus these may inject RF into the radio.  The point here is
longer the feed line, the further away the antenna is the less likely
one is 
to experience RFI issues.

In my case, my operating position is on the 2nd floor of a wood frame
I have no ground other than the AC 3rd pin ground for safety purposes.
antennas are either fed in a balanced configuration with open wire feed
coax feed with a 1:1 current balun at the feed point.  Running legal
on any band, any frequency I have NO RFI issues with any of the 3 Tentec

radios that I own and use.  Same true for the Collins S-Line.  (See my 
call/pix on QRZ.COM).  I have 2 operating positions with the 2nd one
at my shop here on the property.  There I run a Paragon for the receiver
the exciter.  The transmitter is either a CCA AM-1000D or a Western
250B.  These are retired and restored broadcast rigs capable of 1KW 
modulated carrier.  Again, the feedline is 125 ft of Andrew 1/2"
with a 1:1 current balun at the feed point for the center fed wire.

Regarding grounding because of concerns for lightning, most hams have a
poor ground system, more correctly poorly designed to the point of
being dangerous, not only to  there personal selves, but their equipment
their homes.  To that end, I offer a copy of my research paper on
Protection for the Home and Station.  It is in Microsoft Word format and
about 175K in size.  If you want it, ask, and I'll send it along.

In conclusion, if you have RFI issues, it's not the radio's fault.

Bob, K4TAX

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