[time-nuts] GPS antenna selection

[Herbert Poetzl]

Dear fellow time-nuts!

I'm currently investigating my options regarding 
GPS antennae (of course for time related purposes)
and I'm really confused by the variety they come
in ... (my apologies in advance for the long post).


Setting:

I'm living in a three storey house with a sloped
roof, a covered balcony and a larger garden with
huge trees on the Austrian countryside (Europe).

I've walked around with my smartphone (older one)
and I get a GPS position fix within 35s in the 
garden (nine satellites shown), within 100s on 
the balcony (also nine satellites), and not a
single satellite can be seen indoors.

The obvious choice would be to put the antenna on
top in the middle of the slanted roof for a perfect
sky view, but this brings a number of problems as
the roof is very hard to reach and quite high.

I have my 'lab' at the floor where the balcony is,
so I'm considering putting an antenna there and
run about 5-15m of coax cable to the GPS receiver.
The advantage there is that the antenna would be
somewhat protected (it still gets very hot during
summer and very cold during winter, but no rain
and no snow) and easy to reach for maintenance.

The third alternative would be to put the antenna
somewhere in the garden and have a rather long
cable running to the house and up to my lab.


Antennae:

Looking on eBay and Amazon shows a huge pricerange 
for active GPS antennae with and without cable. 

It seems to start at about 10 bucks with rather
small black boxes [1] designed for cars, probably 
containing a 25x25 ceramic GPS antenna and an 
amplifier, progresses over very interesting out-
door constructions for boats and whatnot [2] in 
the 20-100 bucks range and finally tops with high 
end devices [3] way above 100 bucks.

The information about the cheap devices is usually
very scarce, but typically boils down to:

 1575.42 +/- 5MHz 
 24-28dB LNA Gain with 10-25mA at (3-5V)

 7dB f0 +/- 20MHz
 20dB f0 +/- 50MHz
 30dB f0 +/- 100MHz

They seem to use RG174 and come with SMA as well
as BNC connectors (and a number of others as well).

The mid range devices seem to use larger antennae
with smaller tolerances (+/- 1MHz) and larger
voltage ranges for the amplifier (3-13V).


Questions:

 - What are the key specifications which need to
   be verified before buying a GPS antenna?

 - How can they be compared based on incomplete
   specifications?

 - Is a place on the roof or in the garden worth
   the trouble over the covered balcony?

 - Are there any typical pit-falls or general
   tips and tricks regarding mounting and cable
   connection to the receiver?

Many thanks in advance and my apologies again for
the rather lengthy post. Please feel free to point
me to previous discussion regarding this topic.

All the best,
Herbert


[1] http://www.ebay.com/itm/99-Good-GPS-Antenna-SMA-Screw-Needle-10m-Super-Signal-Navigation-DVD-Antenna-/171802461614
    https://www.amazon.com/Waterproof-Active-Antenna-28dB-Gain/dp/B00LXRQY9A

[2] http://www.ebay.com/itm/Standard-Horizon-XUCMP0014-GPS-Antenna-f-CP150-CP160-CP170/331364914004
    https://www.amazon.com/Garmin-010-12017-00-GPS-GLONASS-Antenna/dp/B00EVT2HSE
    https://www.amazon.com/SUNDELY®-External-Marine-Antenna-connector/dp/B00D8WAVTC

[3] http://www.ebay.com/itm/NEW-FURUNO-GPA018-Gps-dgps-Antenna-/182223355414
    https://www.amazon.com/Garmin-nmea-2000-orders-over/dp/B0089DU96A