[time-nuts] GPS Antenna Feed Line Decision

[Clemgill]

Hi Clay,
Intersting subject.
What design for ultra stable/clean power supply are you using please ?
Thx,
Gilles.

> On Sep 2, 2017, at 22:47, Clay Autery <cautery at montac.com> wrote:
> 
> PCTEL GPS-TMG-HR-26NCM Antenna. 
> http://www.neobits.com/pctel_maxrad_gps_tmg_hr_26ncm_high_rejection_gps_p2769137.htm
> 
> Can't say what the gain tolerances are, but it appears to be a pretty
> decent quality part.
> 
> The distribution amp is an HP 58516A GPS L1 Distribution Amp with the
> external power supply tap which will be fed with an ultras stable/clean
> adjustable linear power supply.  As I understand it, this is a unity
> gain amp, so there should be little to no insertion loss or distro losses.
> 
> The distribution amp will be mounted near the devices such that amp to
> device jumpers will all be < 1 meter/3.28 feet.  Likely a lot less.  ALL
> Times N-connectors until reaching a connector TM doesn't make.
> 
> ______________________
> Clay Autery, KY5G
> 
>> On 9/2/2017 3:26 PM, Bob kb8tq wrote:
>> Hi
>> 
>> A lot depends on what comes after the feed cable. The “disto amp” will determine 
>> a lot. You likely need 10 db of net gain in front of it to keep things running ok. For an
>> antenna that is *really* 26 db (as opposed to 26 db +/- 6 db), that would come out to
>> 16 db of feed line loss. This isn’t a terribly surprising outcome. The antennas are designed
>> for installations that run 150’ or more of coax ….
>> 
>> Bob
>> 
>>> On Sep 2, 2017, at 2:57 PM, Clay Autery <cautery at montac.com> wrote:
>>> 
>>> Having decision-making problems for the materials for my GPS main
>>> feedline.  Going to use a TM LMR stock, just can't decide how big to go
>>> with it...
>>> 
>>> 26 dB 5vdc antenna on top of a 38 foot mast.  Feed will come down the
>>> inside/center of mast and exit near the bottom, thence routed through a
>>> window and to the GPS distro amp. Antenna will feed GPSDO, NTP Server,
>>> Blitzortung System Blue station, and one other device TBD.
>>> 
>>> Just cannot decide how big to go with the antenna to distro amp feed... 
>>> Assuming 50 feet total (38' mast + 12 feet to amp in shack) @ 1800 MHz
>>> (closest to 1725 MHz), here are the losses from just this piece
>>> (ignoring the amp to device jumpers):
>>> 
>>> -240 = 5.45 dB XXX - too much loss?
>>> -400 = 2.85 dB
>>> -500 = 2.30 dB  XXX - too hard to find
>>> -600 = 1.85 dB
>>> -900 = 1.25 dB
>>> 
>>> Money not necessarily a consideration as this is a short run for a
>>> permanent installation.  Don't anticipate ever moving the GPS antenna to
>>> the tower.
>>> For 900 and likely 600, likely would not be able to do it in one piece
>>> as routing it out of the mast and into the shack would get complicated. 
>>> Would likely bring it out of the mast at the bottom with a right angle
>>> connector, and then use a smaller diameter jumper for the last 12 feet.
>>> 500 is pretty uncommon stock wise and it and connectors are harder to find.
>>> 
>>> I already have the tooling for both 240 and 400... but I definitely
>>> don't want to challenge ANY of the devices for signal gain.
>>> 
>>> So it mostly boils down to easy vs. more effort ($$ aside)....  Is it
>>> worth the additional trouble to move from -400 to -600 or -900?  To NOT
>>> lose the 1-1.6 dB additional?
>>> 
>>> I'd appreciate your recommendation and reasoning. Thanks in advance!
>>> 
>>> 73,
>>> 
>>> -- 
>>> ______________________
>>> Clay Autery, KY5G
>>> MONTAC Enterprises
>>> (318) 518-1389
> 
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