DVB-S FBC: understanding eight reception paths

Two satellite inputs can supply eight transponders simultaneously. The antenna installation determines which transponders are available. FBC does not remove the restrictions of a conventional satellite cable. With eight correctly configured Unicable user bands, however, eight independently selectable reception paths become available.

What does FBC mean?

FBC stands for Full Band Capture. A broadly captured input spectrum feeds several demodulators. Each demodulator processes one transponder, which may carry several television and radio services. The DVB-S FBC blocks covered here have eight demodulators and two RF inputs. FBC as a general technology name does not guarantee this count for every hardware design.

Term	Meaning
FBC block / module	One reception unit sharing input circuitry between several demodulators
SAT IN A and SAT IN B	Two physical coaxial sockets; case labels may differ
Root tuners A/B	The tuners associated with the two inputs of the satellite block shown here
Virtual / internal tuners C–H	Additional real demodulators with internally assigned signal paths; not six more sockets
Transponder	A reception package identified by frequency, polarisation and satellite position
Channel / service	One individual programme within a transponder
User band / SCR	An individual reception frequency in a Unicable system carrying a requested transponder

The letters are examples. Another tuner order may place the block later in the alphabet. Identify the block and its two inputs, rather than relying on letters alone.

Native tuner selection: the eight satellite demodulators in this Unicable example have individual SCR assignments. Hardware names in the screenshot belong to the example receiver. Open original image ↗

Which connection do I have?

Connection	Available simultaneously	Setup guide
One cable from a universal LNB or conventional multiswitch	Up to eight transponders from one currently selected satellite plane	One universal feed
Two independent conventional subscriber feeds	Up to eight transponders from up to two selected planes	Two universal feeds
One Unicable cable, eight exclusively assigned user bands	Eight independently selected transponders from the positions and planes provided by the installation	Unicable step by step
Two feeds from different fixed satellite positions	Each input’s own position and selected plane, eight demodulators in total	Separate Astra and Hotbird feeds
Fixed dish plus separate motor dish	The fixed position plus the motor dish’s current position, still subject to plane restrictions	Fixed dish and motor

A single universal LNB with one output does not become two independent feeds when a splitter is added. A Unicable LNB, however, can supply several independent reception paths through its one SCR output. The number of sockets alone therefore does not identify its capabilities.

“FBC automatic” or “FBC SCR (Unicable/JESS)”?

FBC automatic is the normal setting for internal tuners with conventional universal feeds. Enigma2 assigns free demodulators to a usable root tuner as required. It does not discover free user bands or configure eight SCRs.

With Unicable/JESS, each independently required demodulator receives its own SCR assignment. Select FBC SCR (Unicable/JESS) for C–H; A/B use the appropriate advanced Unicable configuration. An unconfigured internal tuner does not replace an assigned SCR. See the complete A–H assignment.

Watching television and recording simultaneously

When one service is recorded, other services on that transponder can often share its demodulator. A second transponder requires another demodulator and must be reachable through the available feeds. Eight transponders is neither a fixed maximum of eight channels nor a promise of eight pictures displayed on the television.

For example, two recordings and live TV from one transponder may share a reception path. Eight recordings from eight different transponders can occupy all eight demodulators. Another recording from an already received transponder may still be possible; a ninth independently selected transponder is not.

Decryption/CI, demux resources, video decoders, storage and network throughput can impose further limits. Fast Channel Change, PiP, streaming, EPG scans and active timers may already occupy reception paths. Greyed-out services do not automatically indicate a faulty tuner.

Common misunderstandings

Observation / assumption	Explanation and next check
“I have eight tuners. Why are some channels unavailable?”	One conventional cable supplies one plane. Check the feed type and planes required simultaneously.
“Two inputs mean 16 tuners.”	Both inputs of the block shown here supply eight demodulators in total.
“A always supplies four tuners and B supplies four.”	Conventional FBC automatic assigns C–H as required; there is no fixed 4+4 split.
“One cable means B must always be disabled.”	The internal feed is what matters: a supported connection lets B share A’s conventional plane. With Unicable, logical B can receive internally through A using its own SCR.
“Equal to A automatically gives B another SCR.”	Equal configuration and an individual user-band assignment are different things.
“Unicable needs eight cables.”	Eight user bands travel together along one suitable coaxial cable.
“I must scan eight times.”	The channel list is shared. One complete scan per required reception source is enough.
“A strong signal proves that SCR allocation is correct.”	Duplicate SCRs may fail only during concurrent use. Compare both numbers and frequencies.

Testing an FBC installation

1. Start with a free-to-air service and check lock and signal quality.
2. Select free-to-air services from different transponders for overlapping recordings. Different channel names alone are not sufficient evidence.
3. With universal feeds, stay within the available planes. With eight allocated Unicable UBs, test up to eight different transponders.
4. Check tuner/service information for resource use. Live TV or a stream may already consume a reception path.
5. Play back short sections of the recordings and check picture and sound. Stop/remove the test timers afterwards.

This tests your own installation. The screenshots show real OpenATV dialogs, but a settings screenshot alone proves neither eight successful recordings nor the operation of an antenna system that was not connected.

Continue with universal wiring, Unicable wiring and all eight SCRs, DVB-C FBC or the signal finder.

Background: Vu+ manufacturer manual, FBC and Unicable, p. 93. Menu and allocation logic: OpenATV Satconfig.py, Enigma2 FBC allocation. Screenshots use OpenATV 8.0; the described wiring concepts are model neutral.