----- Original Message -----
From: "mch" <[EMAIL PROTECTED]>
To: <Repeater-Builder@yahoogroups.com>
Sent: Saturday, June 04, 2005 9:50 PM
Subject: Re: [Repeater-Builder] HJ9-50 loss
> Why is that? Does the feedline start acting like an antenna (or dummy
> load) when the conductors are 1/4 wavelength apart or something?
>
> Joe M.
>
Waveguide modes are set up when the internal lateral dimensions of the coax
approach a half-wave at the operating frequency. These modes can
destructively cancel causing very high losses. In building a Ku-band
satellite uplink, I once had a technician puzzling over why his RG-213
jumper wouldn't pass 12 GHz. I put it on a sweeper and showed him that
about 9.5 GHz, the losses shot up tremendously. That's why you always see
small coax on microwave equipment (or waveguide).
Hap Griffin
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