Comtech EF Data CLO-10 - Manual (Page 56)

CLO-10 Link Optimizer Revision 1
Modem and Optimizer Configuration MN/CLO-10.IOM
5–6
5.2.4.2 Link Access Setup
For establishing a link when using Carrier-in-Carrier ® , follow these suggested procedures:
1. Uplink and Downlink Setup – Set up the uplinks and downlinks for the appropriate IF
and RF frequencies. The CLO-10s on both ends of the link should now be tuned to the
same IF transmit and receive frequencies.
2. Link Access and Testing – The standard link access procedures that are normally
performed to verify non-CnC links over the satellite should be used with the CLO-10
configured in BYPASS mode. The link access procedures need to be performed in a
single direction; that is, one end of the link at a time transmits, and the other end listens
(transmit is muted). This will verify link performance in each direction.
3. Link Power Balancing – At this point, it is appropriate to balance the link power. This
means that both carriers should be presented to the CLO-10 at about the same power
from the downconverter output. This can be done by using a spectrum analyzer and
monitoring the spectrum at the output of the downconverter.
4. CnC Full-Duplex Link Access and Testing – The link access procedure from the
previous step should be repeated with the CLO-10 configured in NORMAL mode
EXCEPT both transmitters should be transmitting. Ensure that the CnC search delay
range encompasses the expected delay through the satellite. Typical delays are on the
order of 220-250ms. Also ensure that the frequency offset between the two carriers are
within the CnC Frequency Offset setting. Both of these can be found under
Config: CnC
Æ CnC Parameters .
5.3 Other Useful Information
The CLO-10 acquisition is fundamentally a correlation operation. As such, it assumes sufficiently
random data on the carrier to prevent false correlation peaks from occurring and causing false delay
results. This is usually not a problem provided the data is randomized with a good scrambler;
however, there are some rare cases in which a PN test pattern can “beat” with a modulator’s
scrambler such that the resulting data can produce false correlation peaks.
One way to mitigate such non-randomness is to narrow the CnC delay range. For example, if the
expected delay is 230ms, set the Min delay to 210ms and Max delay to 250ms to mask out the false
peaks – the narrower the better, the faster the acquisition.
Synchronous scramblers often display artifacts which can cause false correlations. Selecting an
asynchronous scrambler can help. Synchronous scramblers usually have better performance, so
narrowing the range should be tried first.
Optimum link performance is achieved if the link is “balanced” – that is, the two carriers are of
equal power. This gives allowance for normal fades to occur on either side of the link. As the link
becomes unbalanced, there will be some slight degradation in link performance but it is no more
than a few tenths of a dB for a typical link.
The bandwidth (BW) setting should be chosen to minimize the processing bandwidth. This
bandwidth sets the decimation bandwidth in the CLO-10. As such, minimizing this bandwidth
also minimizes signal processing ingress noise. For example, if the carrier’s 3dB bandwidth is
364kHz, set the bandwidth to 512kHz.