Narrow band Television
Narrow band Television
|
Transmission of NBTV is limited by the transceiver used. There for the frame rate and resolution is some what limited. Most if not all users have standard SSB HF transceiver and a sound card. At this point I will explain the problems that apply to NBTV. Modulation system used Orthogonal Frequency Division Multiplex (OFDM). The FM carries is dependent on the number of lines in the picture, one line per carrier. There two formats that I like there both 96 x 72 line. One is the RGB 3 pilot carrier; this mode takes 9 seconds per frame. The other is 96 x 72 line, colour difference 2 pilot carrier; it takes 4.5 sounders per frame. Under good conditions both modes work very well, when the signal is week the RGB mode butter of the two. On 20 meters under stable conditions colour different mode is faster one. Problems to look out for when setting up Con (ZL2AFP) software, I have listed below. 1 Linearity of the sound card that is used, not all cards are the same. By experimenting with different type of PCI cards I found that the Creative labs sound Blaster is best to use. Next the linearity of the HF amplifier, more power is always the answer. ALC auto gain controls can a problem as well. 2 Frequency stability is very important the modulated carriers are only a few hertz apart. Older VCO transceivers are a problem for this mode. For receive you need to within one hertz of the transmitted frequency. With both modes there is a turning window and a find turn slider to centre up on. This TV mode can only get better over time. The plan is increases the transmission bandwidth up 10 kHz. Sound has been work on in time this will be added. One frame per/sec at 96 x 72 colour is a good possibly over wider bandwidth. By using software defined radio I & Q transceiver or Soft-rock kit will give freedom in this area. |
 |
 |
 |
The transmitter window is displayed above, showing the BBC test card. When this program starts the TX software there is a sound card select window that comes up. When you click ok the transmitter is displayed. |
The receive program is displaying the same test card as it is been received. This was done via a loop back test to show what a NBTV picture looks like. This software works well under win 2k and XP but not in Vista at this time. |
|
ZL2AFP NBTV Software downloads |
|
|
ZL2AFP NBTV Software update
Two new modes one is digital and other is an analog mode based on FM modulation in the same way as SSTV works. But using digital timing in the way of a correlator using BPSK modulation. So end up a new mode that has best of both type of modulation. |
All these signals were recorded off air on the 80 meter band. ZL2AFP Digital ZL1BPU New analog mode 128x96 ZL2AFP New analog mode 128x96 |