Wegener Communications 6420 - Manual (Page 73)

iPump 6420 User’s Manual
www.wegener.com 800070-01 Rev B Chapter 3, Page 69
3.2. Basic IRD Functions
3.2.1. Transport Front-end
DVB Tuner
The standard configuration of the iPump6420 features a front-end DVB RF tuner. The unit
will, at initial reboot, or after a user (local or Compel) changes the applicable setting, attempt to
acquire “lock” on an RF carrier, presented at its RF Input. In this case, “lock” is an intricate
series of recursive steps, starting with carrier frequency lock, symbol-rate lock, inner
convolutional FEC pattern lock, de-interleaver pattern lock, and finally outer Reed-Solomon
FEC pattern lock. When all these are achieved, the DVB tuner hardware signals the unit
software that “carrier lock” is achieved. In some cases, before “lock” is accepted, the unit must
further verify the validity of the carrier. If WEGENER Carrier ID Tags are in use and required,
then the carrier Tag must match that expected by the unit software. If not, then the acquisition
process resumes.*
* Carrier ID Tags are generally only needed for very narrow-band carriers and/or situations with large LNB frequency offsets.
In addition to the permanent unit carrier settings, the i6420 provides the user with a Preset
Table, an internal list of alternate carrier tuning settings. These may be used as canned
shorthands for users to use, rather than remember all the individual settings for alternate carriers.
The Preset Table is also significant for support of Automated Recovery (see Section 3.1.8).
For an ASI-input option, a much more limited set of steps is needed to detect the ASI
Transport timing, and then find symbol and frame-timing lock on the incoming baseband signal.
At any rate, the result, for either Transport option, is that a valid MPEG Transport stream is
presented to the unit’s internal software Demultiplexer.
Key unit indicators, at this stage are:
1. TRANSPORT LED on for good Transport, flashes if RF carrier lock OK, but
Transport not usable (such as if encrypted)
2. Estimated RF signal level (shown as a unit-less metric 0 to 100 where 100 is highest)
3. Estimated link Eb/No in dB, a metric for signal-to-noise ratio
4. Error’d Seconds (one second intervals with Transport packets with errors)
Tuning Parameters
The unit has a primary set of DVB tuning parameters needed to get carrier lock, plus some
supporting data structures. This list includes the following:
1. ASTRA Universal LNB On/off (generally a factory or local user setting)
2. LNB LO frequency (generally a factory or local user setting)
3. Carrier downlink frequency
4. Carrier modulation
5. Carrier Transport data-rate (or Symbol-rate, for modern DVB-S2 systems)
6. Carrier inner FEC ratio (may be omitted for modern DVB-S2 systems)
7. Carrier ID Tag (‘15’ means “do not use”)
8. Program number (Significant only when any audio port is assigned as “Follow
Tune”, used to remain compatible with legacy systems)
9. Add Preset Table entry
10. Edit Preset Table entry