Centralised TV System Problem

[mtobe]

From what I see and read in this thread, it looks like your trying to make up a small local CATV system.

Your going to have troubles with intermod when trying to add odd and even channels in the same frequency band (UHF) to the system, when channels 21 and 22 (or any two adjacent channels) are combined the intermod (frequency A + frequency B = frequency C) will wipe out a third channel higher (or lower) in the system.

What is done in the CATV business is to put the channels in different bands, this will separate out the odd and even channels so all adjacent channel intermod problems are eliminated.

I don't know if you can use the VHF band or get channel converters/ modulators to do this, but there is no way to use all the odd and even channels you want to in a single UHF setup, (channels 21 to 69) not with out some very expensive channel combiners, modulators and IM filters.

Thanks everyone . I think my limit is 24 channels

 

[Fisty McB]

If the satellite RF outputs are analogue then the usual rule is to avoid 'CH + 5' and 'CH + 9' otherwise the harmonics will cause interference.

In the UK at least the +/-9 channel rule was largely thrown out the window when Channel 5's analogue network was being developed, as numerous main and higher powered relay sites broke this rule. As examples Black Hill in Scotland & Preseli in Wales both transmitted on E37 + E46, while in the English Midlands Lichfield broadcast on E37 with nearby Sutton Coldfield transmitting on E46. The Wrekin, Bilsdale & Darvel also had E26 + E35 transmissions from common sites. I'm sure there's others too, I think the Peterhead relay in Scotland had E59 + E68. The only +/-5 channel example I could find was Huntshaw Cross which had Channel 5 on E67 with another transmission on E62 (though C5's TX ERP was limited to 2kW compared to 100kW for the main four). Again from memory I remember reading that the +/-5 channel difference was more important to avoid in order to avoid problems with the intermediate frequencies used by TV tuners the same way that the 10.7 MHz rule exists for FM radio.

 

[Channel Hopper]

Thanks everyone . I think my limit is 24 channels

Yes it is.

So far you have only planned 22, How many do you want on the system ?