Please take care that the S14WI is "smart": if it doesn't sense a DC current on the antenna port then it reports that to the user ports and I think it can even power off the internal amplifier, this can account for the observed loss instead of the gain.
On Thu, Oct 11, 2012 at 11:20 PM, Magnus Danielson < [email protected]> wrote: > Dear fellow time-nuts, > > I have fooled around with the network analyzer on a set of GPS splitters > in order to illustrate the differences. > > The goal has been to measure: > > 1) Gain (input to port 1 and input to port 2) > 2) Group delay (input to port 1) > 3) Port isolation (port 1 to port 2) > > I have measured these devices: > > A) GPS networking passive splitter > > This is a passive broadband splitter. > > B) GPS source S14WI > > This is a ruggidized "smart" 4-way splitter. > > C) Symmetricom 58536A > > A "smart" 4-way splitter. > > I used a 5 V supply on a spare port for the B and C splitters. > > Please see the attached files. > For each I used a 1.1-1.7 GHz wide-band sweep, and I did a 1.57542 GHz > 102,3 MHz wide sweep. The later sweep range was chosen as 10,23 MHz is the > basic unit for GPS modulation, so you can see how many multiples the skirts > cover. Narrow-band C/A only is only 2.046 MHz wide, where as Narrow-band > C/A+P(Y) is usually around 20.46 MHz wide. Further, for the narrow sweeps I > focused on the group delay read-outs. This is not an ultra-clean, all > calibrated, full compensated measurement. > > The GPS Networking splitter has a fairly flat gain with about 4.5 dB loss. > The isolation is about 25 dB in L1 and 20 dB in L2. Group delay is very > flat at about 1.1 ns. This is expected. I didn't power this one, as I knew > it was passive. > > The GPS Source S14WI splitter I expected to have gain, but found the loss > to be about 20 dB in L1 and about 26 dB in L2. The isolation is about 48 dB > in L1 and about 58 dB in L2. Group delay is a little rocky, but is around 3 > ns. > > The Symmetricom 58536A splitter I expected to have unity gain, but found > loss to be about 14 dB in L1, and L2 is suppressed to 54 dB loss, as > expected. It is clear that this is a filtered product, and this is also > stated in the datasheet. The isolation for L1 is around 28 dB, which is > high from the expected 50 dB. The group delay clearly shows to peaks at > 26,129 ns and 21,889 ns, which translates to Q values of about 124 and 104 > respectively (withdrawing 1 ns for "electrical delays"). > > This is the results of a quick-and-dirty measurements, leaving many > details done sloppy, like unused ports left open instead of terminated, not > following up on the gain structure misses, not doing full calibration etc. > It's to show what some modern available splitters perform like. I really > don't have the time to play these games this week, but I wanted to get > started at least. > > I hope you enjoy the results never the less. > > Getting 50 dB isolation is possible. It seems open ports remains an > isolation issue thought. > > The Symmetricom 58536A provides filtering, leaving a quite noticeable > group delay. It does have the benefit of providing improved suppression of > side-band signals. > > So, you milage will vary. I hope this little lab-report encourage you to > look more at your splitters, measure them and get your hands dirty. > > 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.
