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



Hi

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
www.qsl.net/ve2dwe 
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