----- Original Message -----
From: "Tom W8JI" <w8ji@w8ji.com>
To: "'TopBand'" <topband@contesting.com>
Sent: Saturday, February 15, 2014 12:00 PM
Subject: Re: Topband: Palomar R-X Noise Bridge
Dielectric losses become evident at 2M with 1500W and at 432 400W of
steady
carrier will heat up even the best N connectors and RG-213. For that
reason
many are switching to the 7/16 DIN.
That has nothing at all to do with dielectric losses.
N connectors have a tiny BNC size center pin.
RG-213 have a woven braid and stranded center conductor making the small
center conductor diameter heating and shield heating even worse.
Jim is correct. Conductor losses significantly dominate dielectric losses
at UHF and lower to the point where dielectric loss is meaningless. There
are exceptions, of course, but not with normal parts.
I didnt say that resistive losses dont dominate but dielectric losses do
contribute.
A N connector center pin is larger than the coax that goes into it so its
loss is not an extra contributor. The mating point of M and F continues that
size and with the dielectric do an excellent job of maintaining 50 Ohms well
into the microwaves....at low signal levels.
OTOH an Amphenol or similar quality UHF connector pair will go up in smoke
as I found out when first testing my HB 2M amp at 1800W into the Bird load.
I used RG-213 only as a size example; others that are in the same genre
including 9913 and LMR 400 contribute their own heat as those migrating from
SSB to digital modes for EME and earthly propagation have been finding out.
Im sure that those running tubes with handles even on 160 have had to
migrate away from the UHF set.
Carl
KM1H
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