Specifications

24 Z-Family Techncial Reference Manual
amplifier (LNA) which is built into most Ashtech antenna assemblies. When using
different antennas with the receiver it should be noted that differences in C/No. can be
seen as a result of the above mentioned factors.
If calibrating the C/No. reading of the receiver with a satellite constellation simulator
at room temperature, realize that the noise figure of the LNA used will degrade the C/
No reading by the amount equal to the noise figure of the LNA.
(C/No.)reading = (C/No)simulator - NF
where:
• NF is the preamplifier Noise Figure in dBs,
• (C/No.)reading is the carrier-to-noise ratio displayed by the receiver in
dB.Hz,
• (C/No.)simulator is the carrier-to-noise ratio at the output of the GPS
simulator in dBHz.
If the user selects to display C/No. for the C/A code (or C/No. for P1 code), the displayed figure
relates to the ratio of the power of the C/A code only (or P1 code only) to the noise power in a 1Hz
bandwidth.
Antenna Reduction
Unless requested by the user, the position solution provided by a receiver is the one of
the antenna phase center. The receiver provides a means of obtaining the position of
the surveyed point rather than the antenna phase center through two commands:
$PASHS,ANT and $PASHS,ANR.
The ANT command allows the user to specify the antenna parameters (such as the
distance between the antenna phase center and the surveyed point). Since the antenna
phase center cannot be accurately accessed, this distance can be entered as antenna
radius (distance between phase center and the side of the ground plate) and antenna
slant (distance between the side of the ground plate and the surveyed point). The
receiver will compute antenna height based on these two parameters.
The antenna radius is usually provided by the antenna manufacturer while the antenna
slant can be obtained with a measuring rod.