[time-nuts] Non-impedance matched antenna cables

[Chris Cheney]

> 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).

If a correct match is a must-have, see 
http://www.tuc.nrao.edu/~demerson/twelfth/twelfth.htm on "twelfth-wave 
transformers". Basically, in series:

75ohm----50ohm(La)----75ohm(Lb)----50ohm

The lengths La and Lb are approx one-twelfth wavelength in the cable.

Continuity for power feed is maintained. 

But, since the L1 free-space wavelength is about 20 cm (cable wavelength 
probably 16-18 cm), one twelfth of a wavelength is rather short - quite 
possibly impractically short as the connectors must be included :-)

Chris
G3RSE