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P300H P300 Series Modem Installation and Operating Handbook Page 202
FAULT MODE SETTING
0 Default (normal) fault detection
1 ISDN Backup (<V2.14) / ISDN backup AND OQPSK Compatibility (>=V2.14)
Software <V2.14: Exactly as defined for Fault Mode 13 (but available in earlier versions).
Software >=V2.14: A combination of Fault Mode 13 (ISDN backup) AND Fault Mode 12 (OQPSK
Compatibility).
2 Telenor (R
eceive fail Transmit Inhibit, RTI)
This additional feature allows the guaranteed shutdown of transmission from a remote unmanned
site even in the event that all M&C is lost. When enabled this remote shutdown is accomplished
by muting the signal to the remote destination, which will then mute its transmit carrier whenever
the `receive input signal is lost` for more than 10 seconds continuously. Specifically:
The definition of `receive input signal is lost` includes demod unlocked, FEC sync lost, RS sync
lost, frame sync lost (if applicable), and Multiframe sync lost (if applicable).
The remote transmit will unmute when all the above alarms have been clear for 5 seconds.
3 Max Sequential decoder gain
In normal operation at data rates of 128kbps and below, to reduce the delay through the sequential
decoder (if selected as the FEC in operation), the decoder processing memory is shortened at the
cost of slightly reduced decoder gain. This option disables the shortening of the memory, and
leaves the maximum memory in circuit maximising the Sequential decoder gain (at the cost of
increased processing delay). In the normal mode (when this function is not active) the decoder
memory is 4096 bits, but at receive rates of 128kbps and below this is reduced to 2048 bits, 64kbps
and below 1024 bits, and 32kbps and below 512bits. This means the maximum delay is 32ms at
128.001kbps, and stays between 32ms and 16ms right down to 16kbps, (below which, with the
minimum 512bits of processing memory the delay increases again above 32ms). The data rate
used to determine the processing memory size is the receive rate including any framing and
Reed-Solomon overheads (as this is the output rate of the sequential decoder). See the separate
note in section 8.4 on page 144 regarding minimising the Reed-Solomon delay.
4 Slow Sweep / Poor Eb/No Acquisition
Satellite modems are one large compromise, and part of this compromise is a trade off between
poor Eb/No acquisition performance and normal Eb/No acquisition speed. The modem is optimised
for reasonably fast acquisition down to an Eb/No of 5dB, and the sweep speed is set to match goal.
This option reduces the sweep speed (and hence increases the acquisition time) by a factor of ten,
but improves the low Eb/No acquisition by approx 0.5dB. It is advisable when using this setting to
narrow the Rx sweep width (if you know the frequency of the Rx carrier to be fairly accurate) to help
speed up the acquisition while sweeping at this very slow rate.
5 Post Reed-Solomon V35 Scrambling
Not available on the P300.
6 Fast Eb/No monitoring
The raw Eb/No information the M&C reads varies significantly and so the Eb/No displayed by the
equipment is a heavily averaged to provide a steady result to display. In some circumstances it is
desirable to have a faster display of Eb/No (eg to track short duration interruptions such as a
helicopter crossing the beam), and this option disables the Eb/No averaging providing a faster
responding, but rather jittery Eb/No display.
7 Severely Degraded Phase noise mode
In response to a customer request to provide operation with a severely degraded receive phase
noise in QPSK, this mode can be enabled. It allows operation with up to 20dB worse phase noise
than the INTELSAT mask (DC - 1kHz), although at the cost of a degraded BER in normal
operating conditions (BER is degraded by up to 1dB compared to `Normal` mode).