Digital DVB-S Details

ATV: The Digital Fork in the Road

TechTalk #74 — By Ken Konechy W6HHC

By now, everyone has heard of commercial Digital Television. Old commercial analog TV transmitters essentially went off the air in June 2009, replaced by digital transmitters. This article attempts to explain Digital ATV and its trade-offs for ham radio operators.

Why Go Digital ATV?

Benefits

Picture quality can be nearly perfect most of the time
Error correction handles noise and multi-path
Advanced modulation yields narrower RF bandwidth
Digital TV components are increasingly available
Analog TV components are disappearing from the marketplace

Digital Video Broadcasting Standards

DVB-C — Cable

Very low-noise, low-loss environment
Supports QPSK through 256QAM
Not suitable for ham radio use

DVB-S — Satellite — ham choice

Designed for high path loss, line-of-sight paths
Multiple FEC layers for robust error correction
MPEG-2 video compression + QPSK modulation
Runs in as little as 2 MHz of RF bandwidth
Standard chosen by most European and US D-ATV groups
Not designed for multi-path environments

DVB-T — Terrestrial

Designed for over-the-air broadcast with multi-path
Uses 16QAM + COFDM (1,705 carriers in 6 MHz)
High SNR requirement and complex hardware
Currently impractical for most amateur use

ATSC 8-VSB — US Terrestrial

US commercial HDTV standard; not used in Europe/Asia
8-level amplitude modulation + MPEG-2 compression
32 Mbit/s gross / 19.39 Mbit/s net in 6 MHz
No low-cost ham transmit hardware; impractical today
Exception: Dish Network uses DVB-S for home satellite

Drawbacks of D-ATV

Weak Signal Reception

Digital TV has “all or nothing” behavior
Excellent picture — then suddenly gone
Transition band is very narrow (∼1 dB)
Hard to locate a weak signal without a spectrum analyzer

Equipment Cost

No surplus satellite transmitting equipment is available
Transmitter + exciter + modulator ≈ $1,200+ to build
DVB-S boards from SR-Systems (Germany) or AGAF
Receiving equipment (FTA set-top boxes) is more affordable

Status and Future

European hams drove a large burst of D-ATV activity from about 2000 to 2004, but many sites went dormant. In the US, only a handful of areas operate D-ATV repeaters — ATCO’s WR8ATV/R, outputting on 1260 MHz, is one of them.

The DVB-S spec is being superseded by DVB-S2 (newer FEC schemes, more complex), which risks obsoleting equipment built on DVB-S designs. Inexpensive transmitter hardware is the main driver that could widen adoption.

References & Links

DVB.org — Digital Video Broadcasting organization
ATSC.org — Advanced Television Systems Committee
SR-Systems.de — DVB-S D-ATV transmitter boards
BATC.org.uk — British Amateur Television Club
Full article: OCARC TechTalk #74 PDF

Planning a Digital-ATV Station

TechTalk #75 — By Ken Konechy W6HHC & Robbie Deckard KB6CJZ, OCARC

Planning a D-ATV station involves decisions on band, modulation standard, transmitter hardware, and receiver approach — each with cost and technical trade-offs.

Band Selection

440 MHz

Very crowded; difficult for D-ATV
RF amps are cheapest

920 MHz

Tight fit; lots of Part 15 device noise

1,200 MHz — recommended

Good compromise for simplex D-ATV
Room for portable and home transmitters
RF amps more expensive than 440 MHz

2,400 MHz

Most room; suitable for D-ATV repeater output
RF amps most expensive

Modulation Standard: DVB-S vs. ATSC

DVB-S (QPSK + MPEG-2) is the primary choice for ham D-ATV. SR-Systems’ ATSC MiniMod board pairs 8-VSB video with MPEG-2 audio — not AC3 (Dolby) — making it incompatible with cheap ATSC terrestrial set-top boxes. DVB-S is also approximately $400 less expensive as a complete transmitting station.

Transmitter Cost Estimates (at 1.2 GHz)

DVB-S Transmitter

MPEG Encoder (SR-Systems) — $290–$360
DVB-S 1xTS MiniMOD (SR-Systems) — $470–$540
First RF amp ∼50 mW — $25–$50
30 W linear PA (Down East Micro 2330PA) — $240
Total: $1,025–$1,190

ATSC Transmitter

MPEG Encoder (SR-Systems) — $290–$360
ATSC MiniMOD (SR-Systems) — $852–$925
First RF amp ∼50 mW — $25–$50
30 W linear PA (Down East Micro 2330PA) — $240
Total: $1,407–$1,575

All digital RF modulations require very linear Class A power amplifiers. The MiniMOD RF output is unfiltered — follow it with two 1.2 GHz stages for harmonic suppression. DVB-S signal width ≈ 2 MHz; ATSC (8-VSB) ≈ 5.5 MHz.

Receiver Alternatives

Alternatives 1–4 receive ATSC signals; alternatives 5–9 receive DVB-S. DVB-S alternatives are generally recommended.

1 — ATSC Terrestrial STB

Cheap (∼$50 new)
Incompatible with MPEG-2 audio from SR-Systems MiniMod
Not recommended with ham D-ATV transmitters

2 — Cable-Ready DTV

QAM + ATSC capable; handles MPEG-2 audio
Requires downconverter from 1.2 GHz to tuner range

3 — PC PCI ATSC Tuner

e.g. Hauppauge WinTV-HVR-1600 (∼$100)
PC decodes MPEG-2 video and audio
Requires downconverter from 1.2 GHz

4 — USB ATSC Tuner (Notebook)

e.g. Hauppauge WinTV-HVR-950Q (∼$70)
Requires downconverter from 1.2 GHz

5 — DVB-S FTA STB — recommended

e.g. Viewsat VS2000 Xtreme (∼$100)
No downconverter needed; tuner covers 1.2 GHz ham band
Composite/S-Video output to any TV

6 — DVB-S STB + HDTV

Same as #5 via S-Video output to an HDTV

7 — PC PCI DVB-S Tuner

e.g. Hauppauge WinTV Nova-s PLUS (<$100)

8 — USB DVB-S Tuner (Notebook) — recommended

e.g. SkyStar USB2 (∼$100)
Direct USB connection to notebook computer

9 — DVB-S STB + Notebook

STB + S-Video-to-USB converter (∼$50 extra)

Conclusion: Plan for DVB-S. Any of alternatives 5–9 will work. The authors chose #8 (USB DVB-S for notebook) and #5 (DVB-S FTA STB) respectively.

Symbol Rates, FEC & RF Bandwidth

TechTalk #76 — By Ken Konechy W6HHC

Video Data-Rate and MPEG-2 Compression

Video Source	Data Rate	Notes
Analog NTSC camera (raw)	168 Mbit/s	A/D digitized, uncompressed
NTSC MPEG-2	2–3 Mbit/s	Compressed; lower = still scene
VHS MPEG-2	1–2 Mbit/s	Compressed
Analog PAL camera (raw)	216 Mbit/s	A/D digitized, uncompressed
PAL MPEG-2	2.5–6 Mbit/s	Compressed
HDTV camera (raw)	1–1.5 Gbit/s	Uncompressed
HDTV MPEG-2	12–20 Mbit/s	Compressed

European hams commonly set MPEG-2 output to 2.5 Mbit/s for PAL. NTSC should be similar, possibly reducible to ∼2.0 Mbit/s (∼22% less due to NTSC’s lower frame resolution).

Forward Error Correction (FEC)

DVB-S uses two FEC algorithms in series, both of which inflate the data rate beyond the raw MPEG-2 stream:

Viterbi FEC — configurable as 1/2, 2/3, 3/4, 5/6, or 7/8. A setting of 1/2 doubles the data rate; 3/4 inflates it by 33%. More redundancy = more correction capability but less usable data bandwidth.
Reed-Solomon FEC — fixed at 188/204 (≈ 8.5% overhead). For every 188 input bits, 204 bits come out.

Together, FEC protects against noise but increases the required symbol rate — and therefore RF bandwidth.

Digital Modulation: Bits per Symbol

Symbol Bit-Packing

BPSK — 1 bit/symbol
QPSK — 2 bits/symbol (DVB-S)
8-VSB — 3 bits/symbol
QAM16 — 4 bits/symbol
QAM256 — 8 bits/symbol

Calculating Symbol Rate and RF Bandwidth

Required symbol rate for a DVB-S QPSK transmitter:

Symbol-Rate = NDBR ÷ (Me × CRv × CRrs)

  NDBR  = Net Data Bit Rate (MPEG-2 output, e.g. 2.4 Mbit/s)
  Me    = Modulation bits/symbol (2 for QPSK)
  CRv   = Viterbi FEC code rate (e.g. 3/4)
  CRrs  = Reed-Solomon rate (188/204 = 0.921)

Example: NDBR = 2.4 Mbit/s, QPSK, FEC = 3/4 → Symbol-Rate = 1.73 Msymbol/s

RF allocation bandwidth: BW ≈ 1.33 × Symbol-Rate → 1.73 MS/s fits in ≈ 2.3 MHz.

Net Data Bit-Rate Table for DVB-S QPSK (Mbit/s)

Values marked * are below 2.4 Mbit/s — insufficient for NTSC MPEG-2. FEC 3/4 at 2.5 MHz or FEC 1/2 at 3.0 MHz are good starting points.

FEC	2.0 MHz SR 1.50 MS/s	2.5 MHz SR 1.88 MS/s	3.0 MHz SR 2.25 MS/s	4.0 MHz SR 3.00 MS/s	5.0 MHz SR 3.75 MS/s	6.0 MHz SR 4.50 MS/s
1/2	1.38 *	1.73 *	2.07 *	2.76	3.46	4.15
2/3	1.84 *	2.30 *	2.76	3.69	4.61	5.53
3/4	2.07 *	2.59	3.11	4.15	5.18	6.22
5/6	2.30 *	2.88	3.46	4.61	5.76	6.91
7/8	2.42	3.02	3.63	4.84	6.05	7.26

* Net data rate < 2.4 Mbit/s; insufficient for NTSC MPEG-2 quality

Conclusion

FEC 3/4 at 2.5 MHz delivers 2.59 Mbit/s — sufficient for NTSC MPEG-2. If NTSC turns out to need only 2.0 Mbit/s, FEC 1/2 at 3 MHz provides high correction capability in half the normal 6 MHz analog ATV channel.

Useful Links

OCARC complete DATV article series
RF Bandwidth calculator for DVB-S/DVB-S2
SR-Systems.de — D-ATV components

Understanding DATV RF Bandwidth in Depth

TechTalk #81 — By Ken Konechy W6HHC & Hans Hass DC8UE

When comparing notes on DATV repeater designs with European engineers, Ken W6HHC and Hans DC8UE found that bandwidth figures for the same repeater could differ depending on which definition was in use. Three common methods exist, each giving a different number for the same signal:

−3 dB Bandwidth

BW_−3dB ≈ Symbol-Rate
Familiar to analog engineers; marks the half-power point
Not recommended for DATV spacing — adjacent signals overlap significantly

Occupied Bandwidth (OBW)

BW_occ = 1.19 × Symbol-Rate
Contains 99% of total transmitted power (3GPP TS 34.121)
Better than −3 dB for spacing, but still lacks a guard band

Allocation Bandwidth — recommended

BW_alloc = (1 + Roll-off) × Symbol-Rate
= 1.35 × SR with DVB-S standard roll-off of 0.35
Simplified: BW ≈ 1.33 × SR (<2% error, easier to compute)
Includes a guard band; standard for satellite band-plan coordination
Signal power is ≥ −26 dB within this bandwidth

Non-Linearity and Power Amplifier Backoff

A DVB-S QPSK signal has a high Peak-to-Average Ratio (PAR). If the power amplifier is driven into compression, intermodulation products appear as spectral “shoulders” on each side of the carrier. Commercial satellite uplink standards require these shoulders to be at least −26 dB below the main carrier; DATV operators should aim for the same.

Achieving the required linearity means Class A operation with output backoff (OBO):

Satellite (DVB-S): PA run 4–5 dB below saturation
Terrestrial (DVB-T): OBO of ∼6 dB required

A single MiniMod exciter typically produces shoulders at −42 dB. A compressed PA can bring those up to only −20 dB — broadening the effective signal and causing adjacent-channel interference.