[time-nuts] how to feed multiple GPS receivers ?

[shouldbe q931]

Hi Bob,  and others that responded off list.

On Mon, Feb 25, 2019 at 2:15 PM Bob kb8tq <kb8tq at n1k.org> wrote:
>
> Hi
>
> On a GPS distribution system the issue of 75 vs 50 ohm cable is pretty
much a
> non-issue. A lot of people have run 75 ohms (like Trimble on the TBolt)
and had
> no problems from this.

This is what I thought, thanks for the confirmation.

> The “TV” splitters are generally spec’d to 2 GHz, so well beyond GPS
frequencies.
> Again, it should not be an issue. There are also cheap multi-port
splitters on the
> auction sites.

Some hints on what to search for would be appreciated.

> DC blocks *are* a good idea. DC loads may or may not be needed. It’s a
try it and see
> sort of thing. Some have been known to simply drop a 50 ohm load on one
port of a
> 8 way splitter and let that be the DC load. You *can* run into issues
doing this ….
> (one device feeds 12V and another is a 3.3V feed …. smoke results …).
Cable TV
> DC blocks are dirt cheap ….

Some DC blocks have been ordered.

> Ideally you want the antenna as high as you can get it. In an urban area
with various
> constraints, that may or may not be very high. Coax losses plus splitter
losses should
> be considered when designing something like this. An amplifier ahead of
the splitter
> is not at all unusual.

To begin with I'm just going to use one of the "puck" antennas in the
window that it is currently in, at which point I'm expecting to discover
that the loss through the TV splitter means that more gain will be
required, or a lower loss splitter.

> With the arrival of world of low cost multi-band GPS devices … put up a
multi-band
> antenna. At the very least L1 / L2 (including Glonass coverage). Ideally
L1 / L2 / L5.
> Much easier to do it right the first time.

The longer term plan is to get a L1/L2 (and possibly L5) antenna and roof
mount it, but stage one is just to get the same feed to the different
receivers.

> Bob

While I'm moderately good at fitting most connectors onto cables, making a
wilkinson splitter PCB or managing to cut coax to exactly the right length
do make on out of co-ax its a little bit beyond what I can get away with in
the workshop kitchen.

Cheers

Arne