Topband: Palomar R-X Noise Bridge

[Carl]

----- Original Message ----- 
From: "Tom W8JI" <w8ji at w8ji.com>
To: "'TopBand'" <topband at 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