[opendtv] Re: News: Microsoft, Philips Offer New White Space Test Results

  • From: "Allen Le Roy Limberg" <allimberg@xxxxxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Tue, 2 Oct 2007 18:00:50 -0400

No imagination needed.   Drove around with Dennis Wallace (?) and his truck
in Washington DC area some years back looking at spectrum analyses and saw
unbelievably bad nulls in the spectral plots at some locations he knew were
especially bad.

One could drive a hundred yards or so from good reception to abysmal
reception.  The transmission antenna heights are pretty low for some DC area
stations, and the terrain is pretty much hill and dale.

Such demonstrations convinced receiver designers that receivers had to be
designed to achieve symbol synchronization despite complete loss of pilot
carrier because of multipath.  At first this was done using Costas loop in
place of quadricorrelation (AFPC to pilot carrier with narrowband loop
filtering).  But most receivers are now using a different technique, the
details of which slip my mind at the moment.  As I recall Broadcom designs
were the first to employ the technique.

Adaptive channel equalization is important to good receiver design.  What is
less discussed but is also very important in a DTV receiver is symbol
synchronization.

Al

----- Original Message ----- 
From: "John Shutt" <shuttj@xxxxxxxxx>
To: "OpenDTV" <opendtv@xxxxxxxxxxxxx>
Sent: Tuesday, October 02, 2007 10:18 AM
Subject: [opendtv] Re: News: Microsoft, Philips Offer New White Space Test
Results


> A possibility but it would only make sense to use the ATSC pilot as the
> narrow spectrum examined.  It would be hard to imagine such a deep null
that
> even the pilot was below -114 db, yet the ATSC signal was recoverable a
few
> feet away.
>
> Like a bullet hitting a bullet.
>
> John
>
> ----- Original Message ----- 
> From: "Allen Le Roy Limberg" <allimberg@xxxxxxxxxxxx>
> To: <opendtv@xxxxxxxxxxxxx>
>
> > The problem with a narrowband detector is that it could be physically
> > located in a spectral null of the TV signal, which null is caused by
> > multipath.  If the detector activated a low-power transmitter, the
signal
> > from the low-power transmitter could interfere with nearby TV receivers
> > outside the multipath-caused spectral null.
>
>
>
>
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