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Re: [IRCA] Antennas for receiving...
KAZ, Thanks for the BoG tips which I'll try out either this coming 3-day
weekend or the next at my parents' house in Pueblo West (aimed at 160 deg
toward NE Mexico). The 935-foot BoG sounds sweet and should work well! The
orientation of the 750' BoG in the Google Earth example at my parents' house
put local 1230-KKPC perpendicular to the antenna. Curiously, 1230 was still
strong off the side, but there were traces of other stations underneath.
When the antenna was raised off the ground by a mere 2 feet, 1230 went WAY
down in strength allowing easy reception of Phoenix and El Centro. Even when
the antenna was on the ground the Tucson Int'l Airport TIS on 530 and Sky
Harbor Int'l Airport (Phoenix) TIS were in nightly. I managed to log about a
dozen NZ and Australia stations with it on the ground including a 1kW New
Zealander on 1206kHz! 73.
Chris
From: "Neil Kazaross" <neilkaz@xxxxxxxxxxxxx>
Reply-To: Neil Kazaross <neilkaz@xxxxxxxxxxxxx>, Mailing list for
the International Radio Club of America<irca@xxxxxxxxxxxxxxxx>
To: "Mailing list for the International Radio Club of
America"<irca@xxxxxxxxxxxxxxxx>
Subject: Re: [IRCA] Antennas for receiving...
Date: Sun, 24 Aug 2008 20:19:53 -0500
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
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