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
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