TV says it is not getting a signal seemingly on alternate channels.

[Jrawlinson]

So, if I select 101 - says no signal, 102 - works fine, 103 - says no signal, 104 works fine.

Higher up the order, it seems to swith from even / odd to odd / even!!

I've done all the basic re-start stuff, the weath is now fine and nothing has been installed / re-installed

[Mark39]

Most likely a fault with your dish setup, either misalignment, a faulty LNB, or  a problem with the cables.

You could try disconnecting and reconnecting the dish cables at the back of your Sky box (make sure the box is turned off at the plug). If it doesn't help you'll need a book a local satellite installer to investigate, unless you have Sky Protect.

Alternatively now might be the time to upgrade to Sky Q - any dish issues will be put right at no additional cost as part of the Sky Q installation.