|[AMRadio] BC-610 terminating impedance|
w5jo at brightok.net
Sat Oct 29 18:13:21 EDT 2005
----- Original Message -----
From: "Jim Candela" <jcandela at prodigy.net>
To: <rbethman at comcast.net>; "Discussion of AM Radio"
<amradio at mailman.qth.net>
Sent: Saturday, October 29, 2005 9:39 AM
Subject: Re: [AMRadio] BC-610 terminating impedance
> Bob Wrote:
> Now about that polarization issue you mentioned. I had
> long in depth conversations with the late Ozona Bob,
> W5PYT concerning this. What I recall is that when
> receiving skip at HF, the polarization is constantly
> changing, and the QSB you experience is in part due to
> that. The other part is vector addition & subtraction
> from picking up the same signal from different paths,
> phase, and time delay. Bob figured that if he
> transmitted circular polarization this would in effect
> reduce QSB at the receiving end. I recall he had huge
> diagonally mounted turnstile dipoles mounted nearly a
> football field high (the top). At my QTH (Austin), he
> was always on the S-meter peg, and NO QSB. That was a
> distance of 250 miles, day and night.
> I myself would be hesitant to put up a 80 meter
> vertical because my buddies close in within Texas
> would have trouble hearing me if they were beyond
> groundwave distance, and before the first hop
> Now how does KC9VF get out so well? Doesn't he have a
> vertical dipole on 80 meters?
> For skip reception, it seems that the transmitted
> polarization, isn't a big issue, but more of a angle
> of radiation issue.
> Jim Candela
Jim did you ever visit Bob, W5PYT at his shack? I was there once a few
years before he died. I missed him but went out to where the transmitter
was located in an old abandoned microwave transmitter site. I would guess
the tower to be about 300 ft. high and so many wires hanging from it a bird
could not fly within 1/4 mile of it.
I didn't see a turnstile, but I would have challenged anyone to spot any of
antenna in that grouping. As for Marv., his antenna is a 193 ft.tower
installed like a broadcast antenna. He operated it for a while without
radials until he could find time to install them. The only difference in
his signal then and now with the radials, is he is a bit louder at my QTH
but not a lot. I always hear his signal and if I loose him, I loose signals
from stations equidistant that use dipoles.
I have a friend that says the antennas are the only black art left. You
calculate what it will do then install it. Then you set about making it
work. I tend to agree with that logic. One thing I am convinced about is
put up a dipole rather than a Vee. The mismatch is minimal but you get the
voltage points up in the air. In that case the ends do not tend to induct
into the ground or surrounding structures, natural or manmade.
I know many people will disagree and use some magic antenna modeling
calculator to prove me wrong, but I get consistently better signals reports
using a dipole at 40 ft. than with a Vee at 55 ft. In Marv's case he has
more tower (wire) in the air therefore more capture/radiation area. And he
also has a good ground system.
At the lower frequencies of BCB you see a lot of stations that you hear day
and night and the low angle radiation tends to extend the coverage at night,
but there are still lobes that will cover closer in. I had a vertical in
Wyoming and was able to work the same stations at nigh that I did in the
daytime. I only had 4 quarter wave radials under it. My signal was not as
strong at night, but I still had "local" coverage with a good enough signal.
I know I am opening a can of worms since so much of this theory depends on
your installation so let the guessing begin.
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