Is there a recommended guard band between upstream channels ?
IE would a 1.6 mhz wide channel at 22 mhz upstream require a guard
if there was another channel at 24 mhz with a 1.6 mhz wide setting ?
Maybe there is a handy Docsis chart somewhere ?
Thanks.
Hi!
I never use any spacing, and I don't think it is required. Other DVB-C/T muxes often have no spacing either. Looking at a spectrum analyzer you can see that the upstreams only interfere on the slope where there should be no valid symbols. You should be able to have one upstream at 22,0 and one at 23,6 if you like.
If possible you should avoid frequencies below 30 MHz since a lot of interference is below that threshold. Also take care not to get too close to your upper limit (be it 30, 42 or 65 MHz or whatever limit you have) since the frequency and phase response (linearity in short) may be bad near the edge. If you have a return band up to 65 MHz and 1,6 MHz channels, I'd recommend 63,2 MHz as the highest center frequency which gives you 1 MHz space to 65 MHz.
Also beware of pilot tones that may be located near the upper frequency limit if you have that kind of equipment in your cable plant.
/Fredrik
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