[time-nuts] What are these towers?

Christian Vogel vogelchr at vogel.cx
Sat May 21 15:54:02 EDT 2011


Hi Jim,

On Sat, May 21, 2011 at 06:56:24AM -0700, Jim Lux wrote:
> there *is* a sort of tangential connection.  One of the more interesting 
> strategies in broadcasting these days is forming coverage areas with 
> arrays of geographically dispersed transmitters, all synchronized well 
> enough that the signals received from all transmitters are appropriately 
> synced.

I live just adjacent to a DVB-T transmission tower, and I've visited the
premises: In case of south-german DVB-T I can confirm that they have
Meinberg GPS receivers for synchronizing.

> I think this is being done with DVB-T in europe, maybe someone will comment?

It is being done like that in DVB-T. The interesting thing to realize is
that you *will* have signal cancellations inevitably for some frequencies
depending on your position with respect to the synchronized
transmitters, and you'll have to choose a modulation that can deal with
this selective fading of subcarriers.

If you also want to be resilient to errors introduced by multipath-reflections,
you'll end up at OFDM which modulates *many* carriers (typically 7000 or so)
at a rather low symbol rate. Then if some of the carriers get mangled, the
forward-error-correction will take care.

Highly fascinating, but most likely completely un-time-nutty :-)

	Chris





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