[time-nuts] GPS Antenna Feed Line Decision
kb8tq at n1k.org
Sun Sep 3 10:34:02 EDT 2017
There is no need to feed the 58516 or the antenna with any sort of super power supply.
It’s just a simple RF amplifier in there. It’s designed to be feed off of the
bias supply coming out of a GPS module. If a module has a dedicated
78L05 style regulator on it, it’s one of the better ones ….
> On Sep 3, 2017, at 2:55 AM, Clemgill <clemgill at club-internet.fr> wrote:
> Hi Clay,
> Intersting subject.
> What design for ultra stable/clean power supply are you using please ?
>> On Sep 2, 2017, at 22:47, Clay Autery <cautery at montac.com> wrote:
>> PCTEL GPS-TMG-HR-26NCM Antenna.
>> 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:
>>> 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 ….
>>>> 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!
>>>> Clay Autery, KY5G
>>>> MONTAC Enterprises
>>>> (318) 518-1389
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