Hi,
Well, if you can avoid reception from ground you avoid both handling
reflexes as well as the thermal noise (300K vs. 3K).
You can't have higher antenna gain, since you want to receive fairly
omni-directional above the horizon, with maybe the first 5-10 degrees
nulled out.
What however is important is the noise-figure and gain of the LNA in the
antenna. You want sufficient gain to make sure that antenna cable
damping is handled and that the GPS signal is sufficiently above the
internal noise of the actual receiver. I have installed low-loss cable
to make sure the damping in manageable.
Cheers,
Magnus
On 01/16/2015 01:58 PM, Li Ang wrote:
Hi
I have a question about the GPS antenna. Since the GPS signal strength on
the ground is about 20db lower than the thermal noise, does the gain of
antenna matter?
2015-01-16 7:01 GMT+08:00 "Björn Gabrielsson" <b...@lysator.liu.se>:
Magnus,
If civilian receivers where to implement L2C and L5 which now is
becoming common, they would gain quite a bit of precision in a similar
fashion. For car navigation, the GPS would know which lane you are in.
There ARE civilian receivers doing this, and has been for quite some
years. And its not from only a few vendors - all the big ones have it -
Trimble, Novatel, Topcon, Javad, Leica, Septentrio and a few more. There
are now receivers tracking "GPS L1/L2/L2C/L5, Galileo
E1/E5A/E5B/AltBoc/E6, GLONASS L1/L2/L3, BeiDou B1/B2/B3, QZSS L1/L2/L5"
The price exceeds my home hobby budget, but so does a replacement
CS-tube
a factory new OCXO based GPSDO and many other things you can sometime
find
at reasonable cost used/recycled.
I naturally meant with a reasonable price-tag, sorry for being sloppy on
that detail, and I do know that there is vendors for those signals.
If we had dual or triple frequency receivers below 500 USD things would
start to be interesting. If high-volume kits would be just twice as
expensive, it would be possible to consider for more luxury models.
Receiver with 24 universal channels each of GPS L1/L2/L2C/L5 is cheaper
than a entry level TCXO-based 19" GPSDO (M300GPS @ Dustin). And about the
same price as a modern Loran receiver. What is a reasonable commercial
price?
But yes, multi frequency GNSS is much more expensive than the Oncore,
Ublox traditionally used in a GPSDO. Is the performance gain worth the
cost? Certainly not for all but a few.
On the oscillator side, we consider everything from XO, TCXO, OCXO, DOCXO,
to devar based designs - BVAs and others, and rubidiums, cesiums and
Masers. What are reasonable price-tags for oscillators compared to various
time transfer capable receiver?
--
Björn
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