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

  • From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Mon, 1 Oct 2007 15:40:07 -0400

Richard Hollandsworth wrote:

> WSD only needs a GO/NO-GO detector--which can be narrowband,
> looking for NTSC Visual and DTV Pilot Carriers.
>
> Sensitivity is limited by the amount of noise power in the
> detection bandwidth. DTV's 6 MHz bandwidth results in a
> thermal noise of about -106 dBm....so for WSD detectors to
> lower thermal noise by about 10 dB, they would need a
> detector with about 600 kHz bandwidth.

That's an excellent point. However it still leaves one wondering, how
come similarly cheap DTT tuners can't be designed to the -106 dBm
sensitivity spec. Which still would make them a whopping 20 dB better
than the best I remember seeing for ATSC tuners.

> PS: Bear in mind that the "Listen and Detect" threshhold
> issue detracts from the REAL issue: OET tests found WSD
> devices cause interference to nearby Digital Cable Ready
> HDTV's (and probably also Cable STB/DVR's and many SAT
> Receivers for same reason) AND THERE ARE NO WHITE SPACES ON
> CABLE....

Hah! Who says that's the REAL issue? Not to me it ain't.

I do believe, though, that these cable problems can be addressed by
better shielding of the cable boxes. Whereas the co-channel DTT
interference, with 1 watt WSDs, will be an ongoing problem. Just like
triac light dimmers are for AM radio. One of those persistent problems
that render the spectrum useless in certain circumstances, such as
apartment living.

Bert
 
 
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