[Top] [All Lists]

Re: [TowerTalk] PL259 Insertion Loss?

Subject: Re: [TowerTalk] PL259 Insertion Loss?
From: Jim Brown <>
Date: Tue, 17 Jan 2012 08:06:13 -0800
List-post: <">>
On 1/17/2012 3:40 AM, Paul Christensen wrote:
> That ties in with why we have a 50-ohm coaxial line standard for most 2-way
> communications purposes and it probably dates back to the Quackenbush era.

I don't think so. 50 ohms was the standard for VHF/UHF communications 
gear because it more closely matched the impedance of the most common 
antennas -- a quarter wave vertical with radials, or a quarter wave on 
the roof of a vehicle.  It did NOT become common in ham radio until the 
days of solid state rigs with fixed tuned output stages, and the 
designers of those rigs chose 50 ohms.

When I started in ham radio as a kid in the 50s, we used mostly RG59, 
because it was closer to the feed impedance of a half wave dipole in 
free space.  Over the years, ham literature like ON4UN's book, which 
plots the feedpoint impedance of a half wave dipole at various heights, 
has made us more aware that 50 ohms cable is a better match to a low 
half wave dipole. I feed my 110 ft high dipoles with 75 ohm coax, and my 
low ones (on Field Day, for example) with 50 ohm coax.

Another point. The BEST RG11-size cables have lower loss than the BEST 
RG8/RG213-size cables by virtue of their impedance, but RG-11 cables 
with smaller center conductors or with copper coated steel center 
conductors have significantly more loss on the lower HF bands than those 
with a big (#14) solid copper center.

There's a tutorial on coax and stubs on my website.

73, Jim K9YC

TowerTalk mailing list

<Prev in Thread] Current Thread [Next in Thread>