[amsat-bb] Re: Coax for UHF to Microwaves

Jim Jerzycke kq6ea at pacbell.net
Thu Jul 19 18:08:51 PDT 2007


IIRC, the maximum frequency is limited by the diameter
of the coax. At some frequency, it begins to act more
like a circular waveguide than coax, and the
attenuation increases dramatically. A Google search
for "coax moding" or something similar should turn up
more information.
73, Jim  KQ6EA

--- Jim Sanford <wb4gcs at amsat.org> wrote:

> Gents:
> I happened upon a chance, at a very small (but fun!)
> hamfest on Sunday 
> to get my hands on some LMR 600 coax, which I'd
> hoped to use at 
> 2m/70cm.  Turns out it was too short for my 110'
> tower (building at 
> base).  In followup, I have a chance of some 1 1/4
> Andrew heliax, or 
> some 7/8 andrew heliax.
> 
> I'd hoped to run one line for 2m (dedicated) an
> another to be switched 
> among 220, 432, 900, 1296, 2304, and 3456. 
> 
> I'm seeking <1db loss at 2m and < 3db on the other
> bands.
> 
> The Andrew datasheet says 3.3GHz is the max
> frequency for the 1 1/8, 
> which I'm really tempted to buy based on price and
> the expensive 
> acccessories that come with it.  BUT, if I take the
> mfr data literally, 
> it won't work on 3456.
> 
> Question:  Does anybody have any idea whether or not
> the 1 1/8 can be 
> "pushed" to 3456?  Or does the loss really start
> screaming up above 3300?
> 
> Thanks & 73,
> Jim
> wb4gcs at amsat.org
> 
> 
> 
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