[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 09:53:15 -0400

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.

Al

----- Original Message ----- 
From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Monday, October 01, 2007 6:50 PM
Subject: [opendtv] Re: News: Microsoft, Philips Offer New White Space Test
Results


> 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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