Re: [IRCA] Antennas for receiving...
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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


_______________________________________________
IRCA mailing list
IRCA@xxxxxxxxxxxxxxxx
http://montreal.kotalampi.com/mailman/listinfo/irca

Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers

For more information: http://www.ircaonline.org

To Post a message: irca@xxxxxxxxxxxxxxxx