It usesĨ0 symbols (modulation time slots) to send this sequence about 2.5 times. With one chance in two billion of a perfect score being caused by noise. The equalizer also corrects for Doppler errors which affect carrier phase, making the use of 8-PSK practical.ĭigital NBTV uses a 31-bit PN sequence borrowed from STANAG 4285, The received data timing to reduce errors induced by the ionosphere, using a signal processing device called an 'equalizer'. To be decoded accurately - the ranging information determined from the cross-correlator is used to correct These radio modems use the PN sequence technique to enable complex high speed data Works with a known pattern to look for, and is a very powerful and sensitive tool. Matches up with the local copy of the sequence. In the receiver to locate the one point in the whole message where the sequence Transmission from which the data can be synchronized. Using BPSK modulation, a pseudo-random binary (PN) sequence starts each packet, and is used to identify an exact point in the The amount of data in the packet varies according to the image complexity, theĬompression level and the level of forward error correction included, but the packet size is constant at 256 symbols plus an 80 symbol header.ĭigital NBTV uses a modulation technique which is widely used by high speed HF radio modems.Ī single 1500Hz phase modulated carrier is used to send both packet sync and payload. So nothing could be more different! The transmission consists of a stream of packets, each containing dataįor a small number of image lines.

It provides completely noise-free and error-free image reception, even on 80m.Wavelet image compression and forward error correction are used.An equalizer system is included to compensate for ionospheric path variation.The modem is high speed single-tone PSK, similar to NATO's STANAG 4285.TCP/IP communications is used between program modules.

It uses separate programs for modem and codec in the transmitter and receiver.

The approach taken for the Digital NBTV mode is completely different, in many senses: The pictures tend to be noisy and individual frames can be marred by multi-path effects, especially when used on the lower bands. First, the OFDM signal is veryĭifficult to tune, especially for beginners, and requires extreme transceiver accuracy and stability. Introduction Transmitting Receiving Picture Replay IntroductionĪ number of problems experienced with the OFDM NBTV system led to the development of this Digital NBTV mode. High speed PSK modem, image compression and noise-free pictures

Digital sstv software