Hi Ken,
it's good to hear from you. I seem to have lost touch with you via e-mail, I suspect that my spam filter has slightly fascist tendencies - HI HI.
KenW6HHC wrote:
I am curious to understand why the symbol-rate of 4000 was chosen. Is the station supporting more than one television stream?? It would seem to be a very high value if only one PAL televison stream is supported??
The symbol rate of 4Ms was initially chosen to be similar to the existing 23cm repeaters in the South of England. As it happens, we are hoping for an NoV (permit) to relay 3rd party traffic (other hams), so it's possible that we'll end up with a multiplex, relaying multiple QSOs, from the site on Winter Hill.
Some of the ex-broadcast DVB-S kit in circulation doesn't work below 6Ms, so occasionally D-ATV QSOs are conducted at the higher rate, even though it's not strictly speaking necessary. The use of 4Ms doesn't seem to be causing problems for DX contacts though. A couple of days ago, G3SMU worked G3UVR on 1255 MHz, over a distance of 40 miles, using only 5mW of RF from the TX.
Not everything in the North West UK is running at the higher rates though; thanks to some "inside information" from G3KKD and a bit of hardware hacking, we can now run the AGAF/DARC boards at 2Ms, FEC 7/8, at roughly 2.5MHz bandwidth on 437.250 MHz:
Earlier today Rob, M0DTS, kindly generated a test card transport stream file at 2Ms (7/8). Here's what Rob's TS file looks like when DVB-S modulated at 1255 MHz:
I'm hoping that Rob will have some time to give me a few hints and tips on using software to generate my own low symbol rate files for testing between 1 and 1.5Ms.
Vy 73 de Darren
G7LWT
