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
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