DVB Signal Intelligence

The BCM4515 tuner includes a blind scan mode that searches for DVB-S and DVB-S2 carriers without knowing their parameters in advance. Combined with the transponder table generator, channel parameter display, and streaming AGC/SNR/NID readouts, you can fully characterize the signals transmitted by any satellite in the dish’s beam — frequency, symbol rate, modulation type, FEC rate, and network identity.

This is signal intelligence at the RF physical layer. You’re identifying what carriers exist and how they’re modulated, not decoding content. The output tells you which transponders are active, how they’re configured, and how strong they are — enough to identify the satellite operator and compare against published transponder plans.

What you’ll measure

• Transponder inventory — frequency, symbol rate, and modulation for every detectable carrier on a given satellite
• Signal quality — RSSI, SNR, and AGC levels per transponder
• Network identity — the DVB Network ID (NID) embedded in each carrier’s transport stream, which identifies the broadcast network
• Lock statistics — carrier lock reliability, glitch count, and signal stability over time

Prerequisites

• Motors homed and calibrated (see Calibration & Homing)
• TV search disabled (see Disabling TV Search)
• A target satellite in the beam — either a known satellite from the Geostationary Census or a position estimated from orbital data
• Serial output logged to a file

Blind scan range

The firmware’s default blind scan parameters cover 18000-24000 ksps (kilosymbols per second) symbol rate range with 0.35 rolloff. This handles most Ku-band DVB-S/S2 carriers. Very low symbol rate carriers (narrowband data channels, occasional-use transponders) below 18000 ksps may not be detected.

Procedure

1. Point the dish at a target satellite. Use a known position from a previous census, or estimate from orbital data.

   TRK> mot
   MOT> a 0 195
   MOT> a 1 42

   Replace the azimuth and elevation with values appropriate for your target and location.

2. Enable the LNA and verify signal.

   MOT> q
   TRK> dvb
   DVB> lnbdc odu
   DVB> rssi 10
   Reads:10  RSSI[avg: 872  cur: 880]

   RSSI well above the ~500 noise floor confirms a satellite signal is present. If you’re near the noise floor, adjust pointing in small increments (0.5-degree steps on AZ and EL) until RSSI peaks.

3. Check the current tuner configuration.

   DVB> config

   This reports the BCM4515 hardware and firmware version (ID 0x4515, Rev B0, FW v113.37 on the G2). Useful as a baseline reference.

   DVB> dis

   Shows the currently configured channel parameters — frequency, symbol rate, LNB polarity. This is what the tuner will start from before blind scanning.

4. Run the blind scan.

   DVB> srch

   The blind scan sweeps across frequencies and symbol rates looking for DVB carriers. This takes several minutes per satellite. The firmware tries each combination and reports found carriers.

   You can check or modify the search mode:

   DVB> srch_mode

5. Generate the transponder table. After the blind scan completes, build the table of found carriers.

   DVB> table

   This produces a list of transponders with their frequencies and basic parameters. For extended information:

   DVB> tablex

   The extended table includes additional modulation and coding details.

6. Examine individual transponders. Select a transponder by index and read its parameters.

   DVB> t 1
   DVB> dis

   The dis output shows the selected transponder’s frequency, symbol rate, and LNB polarity. Cycle through all found transponders (t 1, t 2, t 3, …) and record each one’s parameters.

7. Measure signal quality per transponder. For each transponder of interest:

   DVB> rssi 20
   Reads:20  RSSI[avg: 945  cur: 940]

   For streaming AGC, SNR, and NID:

   DVB> agc

   The agc command streams continuous RF AGC, IF AGC, SNR, and NID readings. The NID (Network ID) is a 16-bit identifier assigned by the broadcast operator — FFFF means no signal or no transport stream. Interrupt with q or any other command.

8. Check lock statistics.

   DVB> ls

   This reports total reads, no-signal count, glitch count, and an NID table. A high glitch count relative to total reads indicates a marginal signal — possibly edge-of-beam or a weak transponder.

9. Repeat for V-pol. The initial scan uses the current LNB voltage. Switch polarization and rescan to find transponders on the other polarization.

   DVB> lnbdc odu
   DVB> srch
   DVB> table

   Many satellites split their capacity across H-pol and V-pol. A complete inventory requires scanning both.

Interpreting results

Transponder parameters

Each transponder is characterized by a set of physical-layer parameters:

Parameter	Typical values	What it tells you
Frequency	11.7-12.7 GHz (Ku-band)	Carrier center frequency after LNB downconversion
Symbol rate	18000-30000 ksps	Channel bandwidth — higher rates carry more data
Modulation	QPSK, 8PSK	DVB-S uses QPSK; DVB-S2 adds 8PSK for higher throughput
FEC	1/2, 2/3, 3/4, 5/6, 7/8	Error correction overhead — lower ratios are more robust
Rolloff	0.20, 0.25, 0.35	Spectral shaping factor — affects occupied bandwidth
NID	16-bit hex	Network identity — identifies the broadcast operator

Identifying the satellite

Cross-reference your transponder list against online databases:

• LyngSat — comprehensive transponder plans for nearly every satellite, organized by orbital position
• SatBeams — searchable satellite database with footprint maps and transponder lists
• King of Sat — European-focused but covers global Ku-band

Match the frequencies, symbol rates, and NIDs you measured against the published data for satellites at the orbital slot you’re pointing at. A good match confirms satellite identity. Discrepancies — transponders you found that aren’t listed, or listed ones you couldn’t detect — are worth documenting.

Signal quality assessment

Metric	Good	Marginal	Poor
RSSI	> 900	600-900	< 600
SNR	> 10 dB	5-10 dB	< 5 dB
Lock	Stable (Lock=1 persistent)	Intermittent	No lock
Glitch count	< 1% of total reads	1-5%	> 5%

Dual-polarization RSSI shortcut

The PEAK submenu’s rssits command measures both polarizations in a single reading without switching LNB voltage manually. From the root menu: peak then rssits. It reports Even_sig (H-pol/18V) and Odd_sig (V-pol/13V) simultaneously. Useful for a quick check before committing to a full dual-pol scan.

Going further

• Track changes over time — satellite operators regularly add, remove, and reconfigure transponders. Monthly scans of the same satellite build a history of its transponder plan evolution.
• Identify unlisted carriers — transponders that appear in your scan but not in LyngSat or SatBeams may be occasional-use capacity (news gathering, event coverage), military/government transponders, or recently activated carriers not yet cataloged.
• Compare satellites at adjacent slots — GEO satellites are spaced 2-3 degrees apart at Ku-band. Point at neighboring slots and compare transponder plans. Some operators (e.g., SES, Intelsat) cluster related satellites at adjacent positions.
• Automated monitoring — script the birdcage CLI to cycle through known satellite positions, run blind scans at each one, and diff the results against previous scans. Alert on new or missing transponders.

Geostationary Arc Census Finding satellites to characterize — the natural first step before DVB signal intelligence.

Console Command Reference Full DVB submenu command inventory including blind scan, transponder table, and DiSEqC commands.