FCC DTV vs analog coverage change maps

[David Moisan]

-----Original Message-----
From: boston-radio-interest-bounces@tsornin.BostonRadio.org [mailto:boston-radio-interest-bounces@tsornin.BostonRadio.org] On Behalf Of Dan.Strassberg
Sent: Friday, January 02, 2009 8:04 AM
To: Robert F. Sutherland; bri@bostonradio.org
Subject: Re: FCC DTV vs analog coverage change maps

My experience, using an unamplified indoor antenna in a pretty good
location (about 0.7 miles west of the top of Belmont Hill and maybe
0.4 miles north of Route 2) is that I have gone for weeks receiving a
perfect DTV picture--and sound (DON'T forget the sound; it's the first

The real problem with ATSC reception is not signal strength;  you only need 15 dB S/N to get a perfect data stream.  Multipath--what we used to call ghosting--is the real problem.  You can have, as I have seen, a 20 dB signal that won't decode because the multipath causes too many errors in the stream.

And there's no easy way to detect multipath on an ATSC channel.  In the early days of ATSC reception, one could use a trick to tune the digital channel by tuning an analog channel nearby in frequency, like WGBX whose analog (44) and digital (43) channels are adjacent.  You can't do that for channels like WBZ whose analog (4) and digital (30) are in different bands, and you can't do that at all come February.  

Analog TV showed a lot of impairments like RFI and ghosting on the screen.  There is no mechanism for exposing such impairments to the tuner, though the tuners are getting better at coping with multipath.  The closest I have ever seen to a good tuning aid is the signal monitor on my Hauppauge WinTV ATSC card.  It has three bars:  one for raw signal strength, one for recoverable bit errors, and a third bar for unrecoverable errors.  There is also a status display for each of the data components that need to be decoded for a good signal.

You need to be a geek to use it.

But it does tell you things, like if you have a strong signal (20 dB or better) and lots of unrecoverable errors, you are having multipath problems.  Or the wind gust blew the trees through the RF path between you and the candelabra.  Or one of my cockatiels walked in front of the antenna.  Things like that. :)

It doesn't help either that several Boston stations won't have full ATSC power for a while, such as 7 (after February), 25 (no analog transmitter anymore), 38 and 56.  At my apartment in downtown Salem I can only get 2, 4, 5, 7 and 44 in digital (analog is worse;  I only get 7 in NTSC) and not all at the same time.