Javier, According to Trimble the Thunderbolt IS 50 ohm at the antenna input. (maybe the sole user of 50ohm F-connectors... ;-) )
See page 3-5, Section 3-4 "Antenna Cables" (page 39) in http://trl.trimble.com/dscgi/ds.py/Get/File-10001/ThunderBoltBook2003.pdf "Note – RG-59 is a 75 ohm coaxial cable. The ThunderBolt and the Bullet antenna are compatible with either 50-ohm or 75-ohm cable. Compared to most 50 ohm cable, 75 ohm cable provides superior transmissibility for the 1.5 GHz GPS signal and a better quality cable for the price. Mismatched impedance is not a problem. Note – The input impedance of the ThunderBolt RF input & its antenna is 50 ohms." -- Björn On Fri, 2008-06-13 at 10:47 +0200, Javier Herrero wrote: > 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). > > Regards, > > 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 > > > > _______________________________________________ > > 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. > > > > > _______________________________________________ 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.
