Hello Nate et al,
RE the two loops at 6 and 12 ft, I think Bill K1DY was talking about dead
band conditions. When there is Es or other like phenomena, all bets are off,
and a low antenna can be quite effective. We actaully did try a 50 MHz test
(in November of 2006) with a small 3 element yagi at 15 ft vs a 35 ft high
single loop. The location was Camelback Mountain in FN21HB (I think), where
the Packrats, W3CCX, operates. The path distance was over 300 miles up to
Maine. I saw a huge improvement with the high loop here in Maine at FN43MJ.
I think the improvement was over 6 dB, and closer to 10 dB. (hard to peg
with band QSB etc) but it was very noticeable. Now that spot on Camelback
was reasonably flat with a drop off in the direction we were trying to use.
There was minimal foliage in the path. Still, with such low antennas, there
is considerable interaction with the ground reflected signal. In short we
still do not have 1st Fresnel zone clearance. (The only way to utilize a
dropp off or cliff, is to hang the antenna over the cliff!) By raising the
antenna, we minimized the interaction with the ground reflected signal and
improved the takeoff angle considerably. The interesting thing about the
test was that the station on Camelback Mtn did not get the big improvement
that I heard in Maine, as the omni pattern of their loop introduced much rfi
crud and his noise floor went way up. Reception on Camelback was a wash
between both antennas. So I guess 50 MHz is always the most difficult
problem in a rover vehicle. In my opinion, a small antenna way up high is
the way to go, but you have to pay attention to rfi issues on any band as
well. A well engineered receiver is a must at any hilltop site in the
northeast. There are many high powered signals that can kill 50 MHz on the
30-50 MHz commercial band as well as 70 MHz and the TV and FM broadcast
freqs. The antenna pattern will affect how your receiver "behaves" as well.
I suppose that if you go out in June, and the band opens wide, then almost
anything will seem to work like a champ, and you will have plenty of fun. My
comments are geared to the lunatic fringe rovers trying to make 300 mile
plus contacts on tropo scatter under dead band conditions. Don't feel that
if you can't get your antenna up 35 ft you must stay home!! The important
thing is to to just go out and do it.
Dave K1WHS
http://en.wikipedia.org/wiki/Fresnel_zone For more info on Fresnel zones
----- Original Message -----
From: "Nate Duehr" <nate@natetech.com>
To: "VHF Contesting" <vhfcontesting@contesting.com>
Sent: Friday, March 07, 2008 1:31 AM
Subject: Re: [VHFcontesting] A question of altitude
> Bill Olson wrote:
>> In real life, at K1WHS, I seem to remember having problem working rovers
>> with low antennas (7-10ft) on 6M, and they nearly always had a drop off
>> in front of them.. I guess what I'm saying is, over a, say, 200 mile
>> path, with the same rover, there didn't seem to be much difference if he
>> was on flat ground or overlooking a cliff.. the signal was still a lot
>> weaker than we thought it should be.. I guess we really need some testing
>> here.. Guess I'll do that in June and report back...
>>
>> bill, K1DY
>
> Anecdotally, my dual W0KVA home-brew 6m square loops, one at 6' and one
> at 12' -- fed with a power divider -- have produced some of the best 6m
> contacts I've ever worked, even compared to many high towered 6m
> beams... both during contests and casually.
>
> No time to model it... it "just works" and I'm not changing it unless
> someone proves to me that something else would work a LOT better. :-)
>
> And of course, when the band is open... it's just open... it doesn't
> matter much. I've got FM01, 02, and 03 from DN70, DM79, DM78, etc...
>
> FM01/02/03 was NO problem -- when the double-hop E-skip was in here in
> 2006. 2007... nada.
>
> Most often, if the band's not up... the first stuff to come in is Texas
> (thunderstorm lines from the Rockies to the Gulf -- tropo) and the Gulf
> states, and California going the other way, usually San Diego.
>
> If the band opens some more, the midwest becomes "easy" and often
> Northern California, Oregon, Washington, Idaho (if there were anyone
> there to work) and then down into Baja and most of Southern Canada and
> Mexico.
>
> If aurora comes up... point north from here and enjoy working the entire
> northern U.S. and Canada.
>
> In other words... for a Rover, having a "feel" for what 6m openings are
> happening and learning a bit about how to listen for callsigns, usually
> tells a better tale about what you'll be able to work, than the height
> of even modest 6m antennas... if the band's up... it's up. Just kinda
> how 6m seems to go.
>
> Nate WY0X
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