> 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 _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
