On Sat, Jan 29, 2005 at 08:56:53PM -0500, K8RI on Tower Talk wrote:
>
> >>
> >>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.
>
> I have an AV 640 on a brand X Aluminum tower mounted on the West end of my
> shop.
> It works very well on 40 and quite good on the rest of the bands except 20.
> The match is good, but it appears to be a good dummy load on 20. I've
> never taken the time to trouble shoot it to find out the problem. It has a
> good looking SWR curve that is very close to what the manual predicts, but
> it neither hears, or gets out well on 20.
I have an AV-640 (currently my only antenna) mounted on a 15 ft. piece
of water pipe which is clamped to the eaves of my roof. It gets out as
well on 20 as any other band (I've worked several countries in all
continents even at QRP levels on all bands 40-10). I'm feeding it with
~75 feet of RG-8X and the VSWR bandwidth exceeds the specification on
most bands, although the cable loss is probably a factor with that.
With a tuner, I've been able to make a few contacts up to 1000 miles on
both 80 and 160 (not that I would recommend it for those bands)
73,
Bob, N7XY
--
Bob Nielsen, N7XY n7xy (at) n7xy.net
Bainbridge Island, WA http://www.n7xy.net
_______________________________________________
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.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|