[time-nuts] Non-impedance matched antenna cables

Javier Herrero jherrero at hvsistemas.es
Fri Jun 13 04:47:42 EDT 2008

I've seen that you're right, Thunderbolt is originally supplied with 
75ft of 75 ohm RG-59 cable, as indicated in the manual... So I've the 
inverse problem: the GPS antennas we have in the roof both have 50ohm 
cable :) So... would be good to change the impedance at the Thunderbolt 
antenna port from 75 to 50 by means of some impedance converter? (of 
course, not altering the DC supply to the antenna).


Javier, EA1CRB

Magnus Danielson escribió:
> Hi fellow time-nuts,
> For those of you that isn't aware of it, using 75 Ohm antenna cables rather
> than 50 Ohm cables is a bad move, as the antenna cable itself will create a
> multi-path system. This article elaborate on reflections i cables:
> http://tycho.usno.navy.mil/ptti/1998/Vol 30_39.pdf
> Nothing new, but needs to be said, especially with Thunderbolts getting more
> popular, as the manual clearly recommends 75 Ohm cable as I recall it. Do not
> listen to that.
> Cheers,
> Magnus
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Javier Herrero                            EMAIL: jherrero at hvsistemas.com
HV Sistemas S.L.                          PHONE:         +34 949 336 806
Los Charcones, 17A                        FAX:           +34 949 336 792
19170 El Casar - Guadalajara - Spain      WEB: http://www.hvsistemas.com 

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