Hi If you measure the input impedance of most low noise receivers, it’s not going to be 50 ohms pure resistive. There are multiple reasons for this. Since the “load” is not a match to either 50 or 75 ohm cable, it’s not that big a deal.
The amp in the antenna with it’s post filtering may or may not present a 50 ohm source. They rarely hit a 14 db return loss spec in any case. Indeed there are a lot of attenuators out there that don’t get to 14 db at 1.5 GHz. Trimble did a *lot* of testing before they put the F connector on the TBolt. They could find no impact at all. Bob > On Jul 28, 2021, at 8:23 AM, Dana Whitlow <k8yumdoo...@gmail.com> wrote: > > Most general purpose passive splitters for the L-band regime are > essentially variations > on the Watkinson splitter, which provides good isolation between the output > ports, if > (and only if) the input port is driven from a matched source. > > So if your GPS antenna, whether active or passive, has a good output match > then > the Samsung's input impedance will not affect operation of the Trimble. > But, again, > this is true only if the antenna's output impedance is matched to the > splitter's > characteristic impedance (including consideration of any impedance > transformation > in the transmission line between the antenna and the splitter). > > I cringe at the cavalier treatment given to line impedances used in GPS > systems. > AFAIK, all GPS equipment is designed for 50 ohms, yet a great deal of such > equipment is provided with 'F' connectors, which invite the use of > inexpensive RG-6 > line, which is 75 ohm cable. In addition to problems with impedances and > loading, > It's a built-in source of multipath, all at no extra charge! > > Dana K8YUM > > > On Tue, Jul 27, 2021 at 3:01 PM Don Cross <cosineki...@gmail.com> wrote: > >> On Tue, Jul 27, 2021 at 2:54 PM ordnit via time-nuts < >> time-nuts@lists.febo.com> wrote: >> >>> >>> Any guess? Do I have to throw the unit from the window? For your >>> reference, I have a samsung unit connected to same antenna via a >>> splitter. The GPSDO is performing very well. >>> >>> >> Hi Ordnit, >> >> I'm hardly an expert, but I wonder about the splitter. Is this a passive or >> active splitter? If passive, it could be the input impedance of your >> Samsung is much lower than for your new Trimble and it is making the signal >> seen by the Trimble too weak. If you are willing to disconnect the Samsung >> temporarily, perhaps you could try connecting your antenna to the Trimble >> only and see what happens. >> >> Don >> _______________________________________________ >> time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send >> an email to time-nuts-le...@lists.febo.com >> To unsubscribe, go to and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an > email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
