[TowerTalk] 75ohm cable

[Rich Hallman - N7TR]

Or try this...at Array Solutions. 50:75 ohm transformer.  Would need one
per end.

http://www.arraysolutions.com/Products/baluns.htm#50:75 ohm Xfrm

73 Rich N7TR


-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of jimlux
Sent: Monday, July 19, 2010 3:58 PM
To: Dave Tipton, W5DMT
Cc: Towertalk at contesting.com; 'Carol Richards'
Subject: Re: [TowerTalk] 75ohm cable

Dave Tipton, W5DMT wrote:
> Back in the old days, I read and heard about the guys feeding their
antennas
> with hardline by putting equal lengts of 50 Ohm cable on each end.
So, you
> have 5 feet of 213, 200 feet of hardline, 5 feet of 213.
> 
> I've never tried it personally, but it does sound viable.
> 


It's actually a bit more clever than that.. it's called a twelfth 
wavelength transformer.

going from Z1 to Z2, you have a twelfth wavelength of Z2, then a twelfth

of Z1, then the Z2 for however long.


Be aware, though, that it's pretty narrow band.

I'd use one of the transmission line calculators and see if the mismatch

at the antenna is that big a problem.  If you're running 1.5kW, I assume

you're running an amp, if it's the usual tube type, then you can adjust 
the output for 75 ohms as easily as 50 ohms, so there's no mismatch at 
the Tx end.
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