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Re: RG-6 quad shield for 72 ohm cable and other antenna questions


I'm using two piece of RG59U foam type of 34" long from tip to tip of the pl-
259! through a T connector and i got swr better than 1.5 on two meter.

Hope this will saved you too much cut and try experiment as i do here... Let me 
know if you can replicate my results with the 34" length.

> Michael,
> If you offset the two antennas as you mentioned, that will give you the 90 
> degree phasing for circular polorization. You only need to keep the phasing 
> ( length of coax) equal between the two antennas for 0 phase shift.
> The second part of the problem is getting half the power to each antenna, 
> this is done with a power divider.
> Lines in 1/4, 3/4, 5/4 etc wavelengths will transform impeadence. You must 
> connect two 50 ohm antennas to a 50 Ohm coax, so one solution is to use two 
> 1/4 or 3/4 wavelength coax of 72 ohms to make each antenna 100 ohms and both 
> in paraell will equal 50 Ohms. Using 72 Ohm comes out to be 103 OHms ( 
> square of the coax matching section divided by the impeadence of the 
> antenna, equals the impedence at the other end of the coax.
> CATV cable is usally a foam type and the Vp varies dependent on the foam, 
> and any deformities in the cable.  The solid polyethlene (Vp .66) dielectric 
> is durable, and stands up better to weather, and is harder to pinch with 
> cable ties etc.
> Caculation is a good  method with polyethlene cables, foam types are better 
> measured and extreem care must be used in handling foam type cables. They 
> are easly deformed.

> > I'm trying to homebrew  a crossed yagi array for 2 meters and since I have 
> > a
> > bunch of RG-6 quad shield cable lying around here from when I had 
> > sattellite
> > TV, I'm wondering if I could possibly use it for the matching/phasing 
> > harness
> > or do I need some other type of 72 ohm coax? I plan on offsetting the 
> > elements
> > a quarter wavelength on the same boom. I've been reading the Satellite
> > Handbook and I'm still a little confused about measuring the electrical 
> > length
> > of the matching/phasing lines. I looked up the velocity factor of the 
> > cable

"It is not the class of license the amateur holds, but the class of the amateur 
that holds the license."

Luc Leblanc VE2DWE
AMSAT 33583
Skype VE2DWE
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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