Re: [IRCA] Antennas for receiving...

["Neil Kazaross" <neilkaz@xxxxxxxxxxxxx>]

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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