Then, if the input is 50 ohm, at least the reflections in the other extreme of the Thunderbolt + cable (i.e., at the antenna side) should not be so bad... I'm afraid that since the cable is alredy routed using the inside-building tubes (in fact it uses the tubing destinated for the TV antenna) is not so easy for me to adjust the cable length :)
Yes, I was also surprised by the use of F connectors... and that made me suspect (with surprise) that the GPS input were 75ohm, but I must confess that I did not read more ;). The antenna I'm using is a Motorola mainly intended for vehicle mounting. Surely not the optimum antenna... but not bad results with the Thuerbolt nor the M12's. I've another antenna, but is a cheap one with magnetic base, only used for a nixie clock :) Regards, Javier Björn Gabrielsson escribió: > 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. -- ------------------------------------------------------------------------ Javier Herrero EMAIL: [EMAIL PROTECTED] 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 _______________________________________________ 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.
