Hi In some cases, you can get away with a 470 ohm resistor on the Tee and leave out the inductor. A lot depends on the threshold of the detect circuit in the GPSDO. Since the signal is normally well amplified before it ever gets to the splitter, adding a small amount of loss generally is not a big deal. Depending on this and that, you may see more loss from the Tee than from the 470 ohm resistor :)
Bob > On Jun 17, 2017, at 10:12 AM, Magnus Danielson <mag...@rubidium.dyndns.org> > wrote: > > Hi, > > At one time I had to design a DC-load since the GPSDO did not experience > enough antenna current due to a different antenna being used. So, a BNC-T was > quickly converted with a SMD inductor and resistor to add 150 Ohm of more > load, and that helped the telecom operator to get their GPS out of "no GPS > antenna" warning and actually accept the GPS satellites it was already > detecting fine. > > Cheers, > Magnus > > On 06/17/2017 02:40 PM, Bob kb8tq wrote: >> Hi >> >> The DC block requirement depends a lot on the design of the GPSDO’s you >> are using. With some GPSDO’s a 50 ohm load on the eighth port of a splitter >> will do a pretty good job of “antenna detect” signaling. In the more general >> case >> of “I didn’t design this beast” dc blocks and dc shunts to ground is the >> best approach. >> This fairly quickly gets you headed in the direction of the HP / Symmetricom >> splitters. >> >> Bob >> >> >> >>> On Jun 16, 2017, at 11:54 PM, Clay Autery <caut...@montac.com> wrote: >>> >>> This brings up some interesting questions: >>> >>> If sharing an active GPS antenna, do you have to DC block all but one >>> receiver port to prevent multiple receivers trying to supply current to >>> the antenna? >>> >>> On say a 26dB antenna (ignoring line loss, power divider insertion loss, >>> et al), what is the effective gain to each receiver? (Sorry, having a >>> senior moment) >>> >>> Should ALL unused ports have 50 ohm +/- 0j terminators on them? I >>> assume so... Thus, it would be "better" to always use the divider with >>> the minimum required ports? >>> >>> I am assuming since this is a receive only situation, it will follow >>> approximately the same rules of physics that dealing with satellite >>> antenna installations. >>> >>> I would LIKE to share one PC-TEL 26dB GPS antenna mounted at the top of >>> my 38 foot horiz.loop mast right at the shack entrance, using >>> LMR-400-DB from antenna to Narda 2-way and thence to my current hacked >>> Nortel GPSDO and my soon to be complete RPi 2/3 w/ Adafruit Ultimate GPS >>> Hat NTP Server. On that mast, the antenna would have a near 360 degree >>> view of the sky completely unobstructed. (Eventually, I expect both of >>> those units to be replaced with commercial units). >>> >>> I'm assuming that I DC block whichever unit is capable of providing the >>> LEAST current at 5VDC... I suspect the Nortel unit can supply more >>> current than the RPi, but that's not a guarantee... And I guess I could >>> block/turn off DC delivery on BOTH units and add a voltage adjustable, >>> current limiting DC injection unit into the line. >>> >>> Thanks. >>> >>> 73, >>> >>> ______________________ >>> Clay Autery, KY5G >>> MONTAC Enterprises >>> (318) 518-1389 >>> >>> On 6/16/2017 7:26 PM, Tim Lister wrote: >>>> On Fri, Jun 16, 2017 at 4:40 PM, Gregory Beat <w...@icloud.com> wrote: >>>>> I have reached the point that I need a 4-port splitter for my GPS antenna >>>>> (outdoor 5 volt). Any recommendations of models >>>>> (HP/Symmertricom/Microsemi) to acquire OR to avoid?? >>>> As we recommended to me when I asked a similar question, the Narda >>>> 4372A-4 was a brand I had not heard of before and didn't come up in >>>> 'gps splitter' searches. I got one on ebay for $24 plus a bit extra >>>> for DC blocks on the n-1 other ports and it seems to work well and it >>>> was handy to have an SMA-based solution as most of the gps receivers >>>> and the antenna pucks seem to use SMA. This meant I only needed 1 N to >>>> SMA converter cable for an external antenna (which has yet to be >>>> externalized...). I found it smaller in real life than it looks in a >>>> lot of the pictures, about the size of a modern smartphone but about >>>> double or more the thickness (the connectors are on the ends). >>>> >>>>> greg >>>>> --- >>>> Cheers, >>>> Tim >>>> _______________________________________________ >>>> time-nuts mailing list -- time-nuts@febo.com >>>> To unsubscribe, go to >>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>> and follow the instructions there. >>> >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
