[time-nuts] GPS splitter

Clay Autery cautery at montac.com
Fri Jun 16 23:54:25 EDT 2017

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.



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 <w9gb at 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
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