DATV transmitting Equipment
Digital ATV Modulators
This page provides a summary of the various modulators (including SDRs) that are in current use for generating Digital ATV (primarily DVB-S and DVB-S2) signals. Five systems are discussed: the DATV Express, the Portsdown Filter-Modulator board, Portsdown Ugly Mode, the Adalm Pluto and the LimeSDR.
DATV Express
The DATV Express hardware was designed, built and marketed (for about $300) by a group of US and UK amateurs and from 2014 - 2018. It is a transmit-only software defined radio (SDR), designed specifically to generate DATV signals (DVB-S, DVB-S2 and DVB-T) on frequencies from 70 MHz to 2450 MHz. It is driven by bespoke software. Initially, this software was PC Linux only, but the most up-to-date software now requires Windows 10. The latest Portsdown software for the Raspberry Pi can drive the DATV Express board to generate DVB-S (only).
Although the DATV Express hardware is no longer manufactured, it remains the most capable board available for generating Digital ATV.
The Windows 10 DATV Express software is still (Jan 2019) actively supported by the team and has now been extended to drive the LimeSDR and the Pluto. Although not officially supported, DATV Express software version 1.25lp12 will also run on Windows 7 (as at Jan 2019).
Portsdown Filter-Modulator Board
As part of the Portsdown Digital ATV project, a filter-modulator board was designed and sold (as a bare PCB or an assembled unit) by the BATC in 2017 and 2018. The price was about £100, and it needed an external local oscillator, and could only be driven by the Portsdown software running on a Raspberry Pi 3. It could generate DVB-S signals from 70 MHz to 1500 MHz.
Portsdown Ugly Mode
The Portsdown transmitter can directly drive one of the Raspberry Pi GPIO pins to produce low symbol rate (< 600 KS) DVB-S signals. These signals are OK for testing across the shack, but are spectrally very impure ("Ugly") and need complex filtering to make them fit for transmission.
The Analog Devices Adalm Pluto
The Adalm Pluto is sold by Analog Devices as an educational tool to introduce students to software defined radio. It can be programmed to generate a DVB-S test signal using the on-board FPGA, and it can also be driven by DATV Express software version 1.25lp12. Communication to the Computer is via a micro USB connector. A separate micro USB connector is used to power the unit from 5 Volts (power unit not supplied). One SMA connector is provided for RF output, a second SMA connector is provided for receiver input. Currently the Pluto does not provide a DC signal on transmit to energise subsequent amplifiers, Users have reported very low output powers (<-10 dBm) and problems with low USB bandwidth.
The LimeSDR Mini and LimeSDR USB
The LimeSDR Mini and LimeSDR USB are designed by Lime Microsystems in the UK and built in the USA; total cost (including import duty) from the USA is about £170. Their primary application is in mobile phone base station technology demonstrators, but they are also very good SDRs for DATV use. Both the DATV Express software and the Portsdown system can drive the LimeSDR Mini and the Lime SDR USB to generate about 7 dBm of DVB-S or DVB-S2. Due to processing limitations, the Portsdown software is limited to about 1MS with the LimeSDR, the DATV Express Software on a PC can achieve 4MS.
Summary
If you can find one, the DATV Express board is probably the best amateur DATV modulator available. For DVB-S transmissions at 2MS and 4MS, the Portsdown with its filter-modulator board is very capable. For new designs, the LimeSDR Mini driven by the DATV Express software for higher symbol rates, or the Portsdown system for lower symbol rates, is the best option.
Comparison Table
| DATV Express | Portsdown F-M | Pluto | Lime Mini | Lime USB | |
|---|---|---|---|---|---|
| Price | N/A | £98 (1) | £129 (3) | £160 | £328 (4) |
| Availability | second hand only | Last few in BATC shop | DigiKey UK | BATC Shop | Mouser UK |
| Freqs | 70 - 2405 MHz | 70 - 1500 MHz | 325 to 3800 MHz (5) | 30 - 3500 MHz | 30 - 3800 MHz |
| Modes | DVB-S, DVB-S2 (2) | DVB-S | DVB-S, DVB-S2 | DVB-S, DVB-S2 | DVB-S, DVB-S2 |
| SR range | ~100ks to 9.9 Ms | ~100Ks to 5Ms | ? | ? | ? |
| Software (7) | DATVX PC & P'down | P'down | DATVX | DATVX PC & P'down | DATVX PC & P'down |
| Pwr at 437 | 13 dBm | 10 dBm | -5 dBm | 6 dBm | 5 dBm |
| Pwr at 2405 | 8 dBm | -17 dBm (6) | -7 dBm | 0 dBm | -7 dBm |
Notes:
1. Requires Local oscillator and LO filter at extra cost of ~£40.
2. DVB-S2 not available on DATV Express with Portsdown Software (yet).
3. Digikey UK pricing
4. Mouser UK Pricing.
5. Can be extended to 70 - 6000 MHz by hacking the firmware.
6. Operating outside specification.
7. Software suitable to drive the system: DATVX PC = The DATVExpress Windows software and P'down = Rpi based Portsdown system