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Re: [TowerTalk] R8 vs 6BTV, etc.

To: Bob Nielsen <nielsen@oz.net>, towertalk@contesting.com
Subject: Re: [TowerTalk] R8 vs 6BTV, etc.
From: Charlie <ad5th@direcway.com>
Date: Sat, 29 Jan 2005 20:13:38 -0600
List-post: <mailto:towertalk@contesting.com>
Bob thanks for the reference to the vertical report but the only download I can find for it is $17.00. What's with that?

Charlie
Ham Radio - AD5TH
www.ad5th.com
Live Blues Music
www.492acousticblues.com




----- Original Message ----- From: "Bob Nielsen" <nielsen@oz.net>
To: <towertalk@contesting.com>
Sent: Saturday, January 29, 2005 7:14 PM
Subject: Re: [TowerTalk] R8 vs 6BTV, etc.



On Sat, Jan 29, 2005 at 12:15:36PM -0800, Jim Lux wrote:
Looking at "off the shelf" multiband HF vertical antennas (i.e. R8, 6BTV,
etc.)..

Are there any significant(! (>1dB)) radiation efficiency differences
between them that wouldn't be swamped by such installation dependent effects
like grounding, nearby stuff, etc.


They all look like trapped multiband vertical monopoles, as far as I can
tell, and they're all about 25-30 feet long.

Presumably there are mechanical differences in hardware, etc., but what I'm
really looking for is any noticeable "power sucking loads" that are inherent
in the design (sure, our vertical has a 2:1 SWR bandwidth of 200kHz on 80..
we have a 10 dB pad in the 80m trap!)



There are certainly differences in the way they are fed. The 6BTV is bottom fed with radials, while the R8 has a choke balun and matching transformer (see <http://www.iol.ie/~bravo/r7_vertical.htm> for details on the similar R7) with counterpoise elements which are much shorter than a quarter-wave radial. The effective length of the R8 is somewhat longer than a quarter wave on each band (I'm not sure if it is an electrical half-wave, however).

The Hy-Gain AV-640 is similar to the R8, but uses top-loading coils and
capacity hats for decoupling instead of traps.  Both of these have
separate vertical elements for the higher-frequency bands.  Neither of
these is rated for 80 meters.

The K7LXC/N0AX report on verticals has some interesting comparisons of
several different models.

73, Bob N7XY
_______________________________________________

See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.

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_______________________________________________

See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.

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