Keysight E8663D, Руководство пользователя

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Keysight E8357D/67D & E8663D PSG User’s Guide 239
GPS Modulation (Option 409)
Real Time MSGPS
2. Click Signal Generator Web Control . Below the graphical representation
of the PSG front panel is a field for entering SCPI commands.
3. Enter the following command in the SCPI command field:
:MEMory:DATA "<GPS:file_name>",<data_block>
where
file_name
is the name of the destination file in PSG memory and
GPS:
specifies the destination directory. Refer to the Programming Guide
for a description of the
<data_block>
parameter.
NOTE
Refer to the Programming Guide for more information on downloading files.
RF Power Level Considerations
When you set up your GPS test signal, pay special attention to the RF power
level delivered to the GPS receiver. Because typical GPS sensitivities are
between -155 dBm and -159 dBm, delivering a GPS signal to your device with
a power level greater than -150 dBm or less than -160 dBm may produce
invalid test results.
If you use a physical connection to apply the GPS signal to your antenna, keep
in mind that most GPS antennas are active (a DC voltage is delivered to the
antenna from the receiver). A DC block is therefore required between the signal
generator and the antenna. For direct connection, Keysight recommends
setting the signal generator RF output power to between -70 and -80 dBm and
using an 80 dB attenuator and a DC blocking device between the signal
generator output and the antenna input of the receiver under test.
If you use a radiated connection, place your receiver in a calibrated test fixture
designed with a link budget that will deliver a -150 dBm to -160 dBm power
level at the receiver antenna.
Using NMEA data to monitor signal power
One method to monitor the receiver’s perceived signal level is to monitor the
National Marine Electronics Association (NMEA) data stream from the receiver.
Most GPS receivers have the capability to output data via a serial RS232
connection in NMEA format. An NMEA message called GPGSV reports the
signal strength of the satellites that the GPS receiver is tracking. The GPGSV
message reports a carrier-to-noise (CNO) value for each observed satellite. As
you monitor this message, increase or decrease the power to the receiver until
the receiver’s perceived CNO values are between 35 and 40. Table 8-1 on
page 240 shows how to obtain the CNO value from the GPGSV message.
The following example is a set of three GPGSV messages. The receiver
produces a maximum of three GPGSV messages every second. The fields are
comma-separated; two adjacent commas signify a field for which a value is not
assigned.
$GPGSV,3,1,12,21,71,000,,27,68,000,34,08,62,000,33,29,52,000,,*71