Hej Björn,
On 12/19/2011 01:00 AM, [email protected] wrote:
There are receivers doing all kinds of 'smart' stuff.
1) PVT could be the output from an internal (kalman) filter or a true
single fix solution. A filtered solution will have less noise, and the
ability to ignore a few bad solutions.
2) Pseudoranges could be smoothed by phase measurements, before PVT
solution is processed. This gives lower noise, but does not increase
accuracy.
3) The correlator tracking loops can be adapted if you know your receivers
dynamic profile (say, stationary/walking/automotive/airborne). Higher
bandwidth makes it possible to cope with high user dynamic. Narrow
bandwith optimised for say stationary user will give less measurement
noise.
4) Knowing the receiver dynamic profile, the internal kalman filter can be
adapted to give less noise in a low dynamic use case.
5) On receivers with external frequency input, you can often tell the
receiver how good your oscillator is, to allow the receiver to adapt its
internal parameters accordingly.
RAIM also helps.
Many receivers will enable you to tune its behavour in more or less
explicit ways.
One the topic in the subjet, I have not experienced trouble with short
distance between antennas. But I prefer to use a signal splitter instead
of multiple antennas. I have heard of installations where multiple GPS
receivers did not work well together using closely spaced antennas.
For non-converting antennas (i.e. most of them) you have the antenna
element, filter and amplifier. Amplifiers is in the range of 20-40 dB
gain. Unless there is a bad design, the amplifier doesn't feedback onto
the antenna element, in which case the antenna element would be a fairly
well-matched radiator, but it would be a bad antenna for any receiver so
it would not go un-noticed. However, the output side feeds onto the coax
through connectors, leakage there could occur. While it is unlikely, you
could get cross-coupling with the antennas amplifiers. Since both
antennas have at least some filtering, this should show up as a raised
background noise-floor as the filters allow (typically 2 MHz or 20 MHz
centered around L1).if cross-coupling occurs. I really doubt that
out-right oscillations occurs.
Also some people have had trouble with receivers sharing the same antenna
signal splitter.
And I assume that it is not the DC loading issue you are referring to?
Sufficient port isolation in splitters should keep issues down.
I suspect it is a small problem today with modern receivers, but you might
be unlucky having specific models that interfere with each other.
It can always be an issue, but maybe not the first to investigate.
Cheers,
Magnus
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