UHF channels that can be used next to each other

[Chappers]

Hi everyone,

I found a website months ago and didn't save it, that stated which UHF channels that could be next to each other, and which should have a gap, for instance, it might have said ch. 21 and 22 can be used together, but not ch. 23 and 24, thereby indicating that you'd use 21, 22, 23 and 25 if you needed four UHF channels. For the life of me I can't find it nor think of a good search string to use in google that holds some hope of finding the info again.

I don't suppose anyone knows the details about this for ch. 21 to 69? The reason I ask is that I'm going to use some spare modulators at work to add some sat channels to the system via the A/V connections, but need to check which should be used and which not.

Thanks!
James

 

[satelliteman]

For double side band modulation this refers to taboo uhf channels and the rules are that you cannot use any channel spaced N±1, N±5 and N±9) from the channel that is in use. That's 1,5 or 9 above or below.

SM

 

[Analoguesat]

This is a good site to use:

_http://www.kat5.tv/taboo_guide.html

 

[Chappers]

Thanks for that info, it'll be very helpful. Out of interest, the one I remember seeing did show some channels together, saying something like 21 and 22 are okay, 23 and 24 are not ok to use together, etc. Does that sound right or like anything you've ever heard before?

The transmitter we're pointed to has the following channel allocations:
C21 - 474MHz - S4C
C22 - 482MHz - MUX 2
C24 - 498MHz - ITV
C25 - 506MHz - MUX A
C27 - 522MHz - BBC 2
C28 - 530MHz - MUX 1
C29 - 538MHz - MUX C
C31 - 554MHz - BBC 1
C32 - 562MHz - MUX B
C33 - 570MHz - MUX D

I notice that adjacent channels are being used, but they are either digital next to digital, or digital next to analogue. Is that to do with what I've read about digital having no problems using adjacent channels?

 

[Analoguesat]

You certainly shouldnt use adjacent channels for analogue distribution. Low power DTT gets away with it due to the built in error correction.

BTW that sites a bit out of date - the Borders transmitters havent been updated for DSO.

 

[Chappers]

Ah, it's all making much more sense to me now. While on the subject of DTT, I have become quite conversant with the MATV system at work as they like me to keep it running as well as I can, and so I've been educating myself (and still am, right now for example) but find searching for information difficult. I wonder if you could advise on DTT please? I am familiar with signal levels of analogue, etc., but have heard that DTT signals should be around 50-60dB at tap-off points, instead of the 60-70dB for analogue. Since our distribution amps output at 105dB, I'd imagine that means DTT levels should be 95dB?

I also read, while searching for a masthead amp, a warning about DTT being more sensitive to amplification and to be careful about the levels by which the DTT signals are amplified. Would anyone be able to expand on that please, as more and more Freeview-ready TVs are being used where I work, and although the DTT seems to be okay on the system, there seems to be break-up on some of the weaker multiplexes at times. Although I understand signal levels will be boosted from the transmitter once the switchover occurs, I want to ensure everything is set up correctly. I'm awaiting a Promax TV Explorer to assist with it, but need knowledge even more than equipment. I know I'm taking on a lot and have shown my lack of knowledge in some areas, but still wish to attack it and learn all I can in the process. I have no other way to learn, and it's expanding my knowledge after years of being an electronics engineer who didn't need to know such details about transmission systems.

Thanks

 

[satelliteman]

For DSB modulation adjacent channels shouldn't be used as per the above rule. For VSB modulation adjacent channels can be used.

 

[Chappers]

Bit of a timewarp here... I know nothing of DSB and VSB and don't know what modulation is being used for the transmitted multiplexes here.

I only know that regardless of someone saying the channel list was out of date in a previous message, the same channels were used for the new digital multiplexes:

There are 6 multiplexes in action, using:

CH21 CH22, CH24, CH25, CH27 and CH28.

So, regardless of taboo, they are transmitting to a good portion of Wales on adjacent channels. How can that be if the N+1, N+5 rule was being adhered to.

The webpage I found years ago and cannot find again stated clearly that some adjacent channels should not be used, but that there were exceptions to the N+1 and N+5 rule and gave a list of channels which could be adjacent.

It mustn't be common knowledge, I suppose. I just wish I could find that website again!

 

[rolfw]

As Analoguesat said above, the rule does not need to be adhered to with Digital transmissions.

 

[PaulR]

Also DSB and VSB are analogue formats.

DSB - Double sideband
VSB - Vestigial sideband (not quite single sideband)

When I reading up about the DSO in our region I came across something called positive and negative offset which, presumably, allows digital transmissions to sit next to each other.