Spectracom GSG-5 series, Руководство пользователя с руководством по SCPI

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modifications, and check the SCPI error after each command. If there is a Parameter Conflict
error, it would indicate that the unit accepted your command, but due to a conflict with a dif
ferent parameter, your parameter value was modified.
The conditions under which a Parameter Conflict may occur include the following:
1.
A Transmit Power value has been requested that is too high . The requested Transmit
Power is within the specified limits, but the External Attenuation setting limits the max
imum power to below the requested setting. Transmit Power is set to the maximum avail
able, rather than the value requested by the user. Increasing the Transmit Power may
lead to an increase of C/N
0
, as described under bullet #3 below. To prevent this from
happening, especially when using the SCPI protocol for making adjustments, always use
the command order described above, and check the SCPI errors after each command.
2.
An Unachievable Carrier-to-Noise ratio has been requested
. The requested value is
within specifications, but the Transmit Power setting is too low to achieve the required set
ting. In this case, the ambient noise power spectral density limits the achievable carrier-
to-noise ratio. The Carrier-to-Noise density will be set to its maximum value, not to the
value requested by the user. The noise generator does not generate any additive noise
in this situation. Increase the Transmit Power, then set C/N
0
again.
3.
A Carrier-to-Noise ratio has been requested that is too low. The requested value is
within specifications, but the Transmit Power setting is too high to achieve the required
setting. The signal/noise generator does not have the capability to generate a noise sig
nal this strong (remember that noise power is more than the signal power – SNR is neg
ative). The Carrier-to-Noise density will be set to its minimum value, not to the value
requested by the user. Decrease the Transmit Power to decrease the required noise
power.
4.
A Noise Bandwidth value has been requested that is too wide. (SCPI command only) In
effect, this leads to the same situation described under bullet # 3 above. GSG accepts
the noise bandwidth setting, but increases the C/N
0
to its minimum value. The noise
bandwidth required depends on the filters of the receiver. You have to search for the
value that is wide enough for your receiver. Set up a relatively strong signal (for
example: -100 dBm, C/N
0
44 dB-Hz), and narrow noise bandwidth. Then increase the
noise bandwidth until the C/N
0
value shown by your receiver stabilizes. It is a good
idea to use the narrowest bandwidth needed.
Note: The receivers use different methods to calculate C/N
0
(or SNR), so
the value given by the receiver may be different from the C/N
0
setting of
the GSG unit.
3.6.2 Signal Generator
Every GSG model can be operated as a signal generator, i.e. to generate one, or—if so
equipped—several satellite signals (with no Doppler), or one carrier frequency.
3.6 "Options" Menu
CHAPTER
3
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User Manual GSG-5/6 Series Rev. 26
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