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Re: [IRCA] Antennas for receiving...
- Subject: Re: [IRCA] Antennas for receiving...
- From: "Neil Kazaross" <neilkaz@xxxxxxxxxxxxx>
- Date: Sun, 24 Aug 2008 20:19:53 -0500
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BOG impedance tends to be around 270 ohms. I have used cable and a homemade
5:1 xfmr, but usually just run the BOGs under my car/truck door directly to
the phaser. I slight missmatch doesn't seem to harm them, noting they are
receive antennas.
Termination thru 270 ohms seems to help the lower mid band..ie around 1050
where the back end is nulled nicely, if using about 330 ft. This frequency
seems to drop somewhat as one increases length. I've mess around with
different values and also some series inductance to try to tweak for better
back nulls, and to be honest, could never come close to being happy across
the band. Long BOGs like 600 ft plus really have some good built in front to
back anyhow since they are so lossy and the back end signals reflect of the
far end, travelling lots further than the incoming wave does. I would not
bother with termination for temporary BOGs and would use them as a Phased
BOG System.
As an example, my northerly TA BOG setup in Grafton WI last Sept was 310 ft
// 183 ft spaced about 2 ft apart and aimed 35 deg. I did a little test
during the day and phased the ESPN local on 1510 out to my S/SSW and had
good nulls all the way up to 1700, and acceptable nulls as low as 1250
(great nulls down to somewhat below 1400) with out any retweaking. Trivial
retweaking could easily re-establish a really deep null.
If you have longer BOGs and want to phase null lower freq pests then a
length difference closer to 200 ft is best. As an example, 680 ft // 490 ft
aimed 65 deg from WI was nice for knocking down WGN (somewhat off the back
end) to allow Canaries and Portugal to be heard during super TA cx a year
ago. The signals from TA land in the low band were enhanced (a bit higher S
meter reading combined than each alone) by phasing back end pests... ie put
somewhat in phase while the back end was out of phase. But if I use that
difference of 190 ft for the high end, the desired DX usually drops a bit in
level..ie is also a bit out of phase.
Shorter BOGs have wider beam widths than do the longer ones, but even 300 ft
will be quite impressive on the high end of BCB. But don't worry about
termination except for permanent installations and regardless, use a shorter
// BOG to phase away back end QRM.
The Phased BOG System if unterminated will be useful off the back end if you
phase away front end QRM, but in comparison to aiming right at the DX, the
back end DX will be a few dB down, but often the directivity will be so
good, you'll get good stuff anyhow.
73 KAZ
----- Original Message -----
From: "CHRIS KNIGHT" <cgknight63@xxxxxxx>
To: <irca@xxxxxxxxxxxxxxxx>
Sent: Sunday, August 24, 2008 1:22 PM
Subject: Re: [IRCA] Antennas for receiving...
Neil,
Re. your terminated BoG, what is the typical value of termination
resistance and how should this vary per wire length? Can you null anything
with just this one antenna alone? Is having just one antenna terminated an
"optimal" situation?
This has me thinking that I could place a temporary BoG system near this
QTH meaning I would have to reel in the wire after every DX session, but
leave the ground rods there. As far as matching the BoG wires to a Quantum
Phaser, would that require a transformer and an additional ground rod at
the feedpoint per wire? 73.
Chris
Fort Lupton, Colorado
http://sites.google.com/site/2008amloggings/
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