ComStream CM601, Инструкция по установке и эксплуатации

Страница: 228 / 228

01-0922-401 Rev. A 4/03
6
It would be very easy, however, for the operator to help in speeding up the initial “out of the box”
acquisition by measuring the offset and programming an approximate offset value to AO. For example, if
the installer measured the offset such as in Figure 3, they would note that the offset is approximately
5KHz. The operator would then type AO 5000 (or AO –5000 if it were a negative offset) and then type
AQ 1 to begin initial acquisition. Initial acquisition would then be greatly reduced.
Power-Up or Fade Acquisition
Once the modem has acquired the incoming carrier and the receive offset has automatically set the
value of the acquisition offset, subsequent re-acquisitions are virtually immediate regardless of the
magnitude of the carrier offset. This is true because with the carrier offset known, the demodulator
“shifts” its center frequency to compensate for any difference between the value of RS and the actual
carrier frequency. Unless the operator sets the modem back to factory default or manually enters a zero
value in AO, the offset in NVRAM will always be equal to the offset of the last incoming carrier
acquisition.
Higher Symbol Rate Carrier Acquisition
With symbol rates above 64ksps, the wider bandwidth and greater symbol rate make carrier
acquisition much faster and easier for the demodulator. As symbol rate increases the acquisition times
typically decrease for any given carrier frequency offset. The modem will, however, continue to store
any offset measured between the programmed received IF frequency and the actual frequency received at
the demodulator.
Technical Support
If you have any questions or need assistance during this upgrade contact ComStream Customer
Service at (858) 657-5454 or fax (858) 657-5455 or email comstream-custservice@radn.com .