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Antenna System RF Parameter
Considerations
It is important
that the gain of the antenna and any losses in the
feeder cable are within set limits for the GPS receiver
to operate efficiently.
Both the gain and
the noise of the overall system affect the performance
of the A/D converter in the GPS10RBN’s GPS receiver.
The illustration
below illustrates typical values for the GPS10RBN
receiver when used with the supplied antenna and the
standard length of 5 meters of cable. The thresholds and
ranges listed should be considered to have a tolerance
of 2 to 3 dB. The figure below illustrates a typical
system.
System Constraints
• The gain in
decibels is cumulative through all stages (i.e. G = G1+
G2 + G3 .. ). The optimal gain of the antenna, cabling
and any in-line amplifiers and splitters for the
GPS10RBN receiver is between 18 and 36 dB.
The GPS10RBN may
operate outside of the optimal gain range but
performance will degrade. Therefore, Precision Test
Systems does not recommend operating outside of the
optimal gain range as indicated above.
For the system
illustrated above, the external gain is approximately 24
dB in front of the receiver.
• System noise (F)
is not to exceed 4dB. The cascaded system noise figure
formula is:
(=1.9dB for the system shown
above)
where ƒ1 is the
noise figure for stage one and
g1
is the gain for stage one. Note that all of the values
used in this equation are
absolute.
The
resulting number must be converted back to decibels in
order ascertain if it is less than 4dB and to compare it
with other antenna systems configurations.
If longer cables runs are needed,
Precision Test Systems supply an antenna amplifier, the
GPS35.
The brochure for the GPS35 GPS
Antenna Amplifier is available
here
For help on choosing the best
antenna and antenna cable, click
here |
