Signal Delay

[wolsty]

This morning, the VHF radio in the bedroom was tuned to Radio 4 for Desert Island Discs. The Freeview box in the living room was tuned to the same programme. I was in the kitchen and could hear both, but the Freeview signal was about 1 second behind that on the VHF set. Both signals were coming from the same transmitter so, if Einstein was correct and the speed of light is the same everywhere, why was there a time lag?

 

[rolfw]

Obvously coming from different places before they reach the transmitter mast Wolsty. In fact everyone is aware that satellite signals of terrestrial channels lag behind terrestrial channels, even the Freeview ones, but Channel 5 is obviously taken from the sat feed, as it lags behind satellite when shown on Freeview.

 

[wolsty]

I knew there'd be a simple answer that I'd missed!

 

[whatsthis]

That makes sense but I think there is more to it than that, here's why.

If I have the dreambox on the same channel as a FTA reciever they are also out of sync. So I think it's the box as well.

 

[wolsty]

Another thought occurs to me. Which channel carries the time signal by which I should set my watch? (It's an academic question, as I use the atomic clock on the Internet).

 

[PaulR]

For the time signal I would use Radio 4 Long Wave ;)

The signal delay could also be due to the signal processing into digital format.

 

[Analoguesat]

Signal lags are quite noticable if you try watching Formula 1 coverage in ITV1 nad RTL at the same time. RTL is always around 3 seconds in front of the ITV programming.

The best explaition I ever got was extra signal processing, probably an extra signal hop, delays in framestores etc. I shall be interested to see how far out of synch they are now ITV1 is fta - they should be closer as there isnt the encoding / decoding time lags involved.

 

[whatsthis]

Do you think that delay is long enough to place a bet ?

(Reminds me of the sting)