[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 18:50:11 -0400

Richard Hollandsworth wrote:

> For 6 MHz, the thermal noise power is about -106 dBm.
> ATSC requires at least 15 dB SNR, hence theoretical
> sensitivity is -91 dBm, which would be reduced to -86
> dBm for a 5 dB Noise Figure (the best I've seen
> specified).

Yes, you make good points.

But again, if you use these figures to arrive at a possible -114 dBm
sensitivity for the WSD free-channel detector, you are saying:

1. The WSD will have no idea at all as to what the RF energy in that
space might be. It just senses something in a 600 KHz spectrum. Which is
about right to include the ATSC pilot or NTSC carrier.

2. The WSD's tuner will have an extremely low noise figure. How do they
achieve this assuming price parity with the DTT tuner? Aren't these
supposed to be cheap consumer-grade devices?

Instead, I would have expected the WSD free-channel detector to be able
to decide whether the channel was used by a TV signal or whether it was
safe to drown out the RF energy with its own 1 watt signal. That would
require it to do more than just sense energy, so it makes the -114 dBm
sound mighty fine. And I was also expecting the price point to be, if
anything, lower than that of a DTT tuner.

> I dunno Bert....you seem to be saying you don't really
> care if condo/apartment dwellers lose the ability to
> tune certain cable/sat channels....

Well, first of all, it's very common for apartment/condo dwellers to
have lost the ability to receive OTA, simply because their external
antenna network was usurped by cable in many cases. That would have
bugged me royally.

Also, the FCC tests used TVs with built-in receivers. Cable companies
prefer that people not use their built-in receiver. It gives them a good
excuse to charge more for beefed-up STBs, assuming their current ones
don't work with WSDs, which is just an assumption.

Bert
 
 
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