[TowerTalk] Sharing a GPS Antenna

[jimlux]

On 8/14/17 7:22 AM, Clay Autery wrote:
> I'm toying with the idea of trying to share a single PCTEL GPS antenna
> three-ways.
>
> I would prefer to NOT have to put up three different GPS antennas, have
> three different feed lines coming into the shack, et al.
>
> Need to feed:
>
> 1) GPSDO (currently a re-purposed Nortel unit) 5VDC spec antenna
> 2) NTP Stratum 1 server (Raspberry Pi-based) Pretty sure a 3.3VDC antenna
> 3) Blitzortung System BLUE lightning detection/reporting station. 3.3VDC
> antenna
>
> PCTEL GPS-TMG-HR-26N antenna is a 5VDC nominal (40mA @ 5VDC) HOWEVER the
> spec sheet shows it functions from 3.3VDC to 12 VDC using a regulated
> supply, and a "survival voltage" of 24 VDC.
>
> Now, I have heard of folks running antennas that function on 12VDC on a
> straight splitter with no DC blocking, but that doesn't "sit right" with
> the OCD over-engineer part of me.
>
> Here are the 3 options:
>
> 1) 3-way split, no DC blocking
> 2) 3-way split with DC blocking on 3.3VDC devices.
> 3) 3-way split with DC blocking on all three devices AND DC injection
> after the split with a chosen regulated DC voltage based on best gain
> vs. minimized noise.
>
> Leaning toward Option #3 because I don't intend to use the old NORTEL
> unit forever... and it's replacement may well NOT be a 5VDC device...
> And I suspect that efficiency drops rapidly below 5VDC.
> That way, nothing changes from splitter to antenna regardless of what
> device I put in place for GPSDO, NTP server, et al...
>
> Cable run will be approximately 53 feet from devices to top of 38 foot
> mast right outside the shack (top of pole used at one corner of 80m
> loop; loop is suspended 10 foot laterally away from mast).
> I know splitting the signal is likely NOT "time Nuts approved" approach,
> but I'd like to try it anyway... and putting the antenna up high in an
> all but unobstructed 360 degree view, and using a low-loss feed-line
> should allow sufficient signal for all devices. (I hope)
>
> Any suggestions for a 3 port DC blocked splitter, or other part(s) and
> some part to use for DC injection?  I can handle the linear regulated
> supply.  <wink>
>


Timenuts will happily split - most GPS antenna units have plenty of gain.

Cable TV splitters are a good start - as to whether or not they have a 
DC block, it probably depends on the kind.

Minicircuits has a bunch of Bias Tees

https://www.minicircuits.com/WebStore/BiasTees.html

One issue is whether your GPS receiver is expecting to see a load, so 
you may need a resistor on the line to fool the receiver into thinking 
it has an antenna hooked up.


You can search the Time-Nuts mailing list at febo.com - this comes up 
all the time.

a search like "site:febo.com GPS splitter" will bring up lots of useful hits