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[TowerTalk] Ethernet, 900 MHz and 160m

Subject: [TowerTalk] Ethernet, 900 MHz and 160m
From: Roger Parsons <>
Date: Tue, 19 Aug 2008 16:16:58 -0700 (PDT)
List-post: <">>
This may not be the correct forum - please forgive me if it is not.

I have a 900 MHz link between my home and my remote station, and at present the 
UHF antenna is at the 240' level on the tower which also carries my 1.8 MHz 
antenna. The radio is in the hut at the base and there is a bi-directional 
amplifier by the 900 MHz antenna. I have had no interference issues at all even 
with a kW on 160m even though the (vertical) driven element is only a few feet 
from the 900 MHz antenna.

I have recently however had interference problems from a local ISP also using 
900 MHz on a tower quite close to mine, to the extent that I have had to change 
the type of 900 MHz radio to a more modern one which lives better with the 
interference. Unfortunately that would also mean that I need to change the type 
of amplifier OR actually put the radio high up the tower. The latter would be 
cheaper, but I am concerned about having roughly a half wave of CAT5 cable 
running parallel and a few feet away from my 160m driven element.

I would intend to choke off common mode at both ends of the ethernet cable. I 
know that the construction of CAT5 cable means that it has good common mode 
rejection, but this is a pretty severe test, and of course the cable length is 
getting rather close to the limit. 

I have had no lightning problems with the amplifier/coax set-up even though the 
tower is frequently struck and I guess the fact that the coax outer is very 
well 'grounded' both at the antenna and the base of the tower may help. The 
same might not be true for ethernet.

Would appreciate any thoughts.

73 Roger

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