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??

greg

On Fri, Jun 16, 2017 at 4:40 PM, Gregory Beat w9gb@icloud.com wrote:

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).

Cheers,
Tim

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:

Clay wrote:

Yes.  Note that you may need to put DC loads on the other receivers to
fool them into thinking they have an antenna attached (otherwise they
may report an antenna fault and refuse to operate).

Splitters often have amplifiers so they provide unity gain to all output
ports.

Best regards,

Charles

I use Mini-Circuits ZN4PD1-50-S+  with added DC blocking  as they are not specifically GPS splitters.  Cheap and effective.

"The power of accurate observation is commonly called cynicism by those who have not got it. »
George Bernard Shaw

I use Mini-Circuits ZN4PD1-50-S+  with added DC blocking  as they are not specifically GPS splitters.  Cheap and effective.

"The power of accurate observation is commonly called cynicism by those who have not got it. »
George Bernard Shaw

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 6/17/2017 7:40 AM, Bob kb8tq wrote:

Hi Bob and list,

This is very good timing for this discussion...as I'm in the same boat.

As others have pointed out, the issue with power splitters not designed
for GPS use, is that they are passive, not DC-blocked, and don't have a
way to load-down the DC-block ports to "fool" antenna sensing circuitry
as other here have posted.

For the folks who like to "roll their own", there is this design for a
DIY GPS antenna splitter:

http://www.uhf-satcom.com/misc/gps_dist/

It uses a MAR-6 MMIC, but since I had none of those in stock here, I
modified it for a PGA-103 amplifier and built onto FR4 using the
toner-transfer / ferric chloride etch method.  Seems to work okay, but
doesn't have DC-load on the ports, just DC-block.  I have not taken it
into work yet to put it on the VNA to see how it does.

I picked up a couple of Mini-Circuits ZC6PD-1900W 6-way splitters on the
e-place very cheap.  And by "very cheap" I mean that even if I destroy
all the electronics inside, the enclosures and SMA connectors are worth
what I paid for them.

I've been toying with the idea of modifying one of the units to add
internal DC-blocking and resistors to ground for DC-load.  For DC block,
seems like I could very carefully slice the trace on the board by the
SMA connector, bridging the gap with an SMA capacitor.  Problem is, when
I add the capacitor, I'm changing the path length.  I believe I could
minimize this by using a very small slice and a very small SMA
capacitor...but I don't know how much this will impact performance.
Perhaps I need to do some modeling of the design and see what happens.
Right now I don't have anything very small, with 1206 being the smallest
I've got.

I also picked up a 40dB PCTEL GPS timing antenna on the e-place, with
the idea being that even if I do use a passive splitter, I'm starting
off with 40 dB gain at the antenna versus the typical 26 dB.  If the
splitters have ~10 dB of loss (what I measured on the VNA at work) I may
need to add some attenuation to knock it back down to 26 dB-ish.  I
don't know what sort of dynamic range these GPS receivers have, so that
might not been needed.

thanks much and 73,
ben, kd5byb

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

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