[TowerTalk] Ethernet, 900 MHz and 160m

Roger Parsons ve3zi at yahoo.com
Tue Aug 19 19:16:58 EDT 2008

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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