[TowerTalk] R8 vs 6BTV, etc.

[Charlie]

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 at oz.net>
To: <towertalk at 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
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