OK, Engineering Types: Explain This Again

[Dan.Strassberg]

As I understand it, part of the information transmitted in a DTV
datastream is the virtual-channel number, that is, the number of the
channel by which the receiver or converter box identifies to the
viewer the channel that is being decoded. In general, the virtual
channel will not be the same as the RF channel, though, in some cases
it will be the same. The example that I know of in this area is
Channel 7, which, after June 12, will be both the RF channel and the
virtual channel. For the sake of clarity, I have not mentioned the
secondary channels (e.g. 44-1, 44-2, 44-3, and 44-4) in this
discussion. Those are also identified in their datastreams.

-----
Dan Strassberg (dan.strassberg@att.net)
eFax 1-707-215-6367

----- Original Message ----- 
From: "Laurence Glavin" <lglavin@mail.com>
To: <boston-radio-interest@lists.BostonRadio.org>
Sent: Saturday, April 25, 2009 1:40 PM
Subject: OK, Engineering Types: Explain This Again


As a previous member of the BRIG mentioned, one reason to get a
digital-to-analog
box, even when one has cable TV in the home, is to be ready during any
hurricane or blizzard
that cuts off cable reception.  And then, for a normal person, a
d-to-a box may be needed
for a table-top TV in the kitchen or other room away from the cable
coneection (my
situation).  But for rf geeks, it also provides endless hours of fun
derived from treating
this equipment as a toy.  In addition to the government-subsidized
d-to-a box, I purchased
a Radio Shack amplified antenna with an internal rotatable UHF antenna
(physically it
resembles the Starship Enterprise).  I have to say that ALL of the
full-power DTVs on UHF
transmitting from either 350 Cedar Street, the route 128 candelabra
and the WHDH standalone
come in with usually strong and consistent signals;  the exception:
very windy days, when
I imagine the towers move to and fro, and thus confuse my receiver.
Anyway, right after
WGBX-TV's analog transmissions stopped, I tuned the box to channel 44
and got WGBX-DT anyway.
Somehow, channels 44 and 43 were stored together in the box's memory.
Then I decided to
delete 43 and 44 from the system, after which I could ONLY get WGBX-DT
by entering '43'.  So
I thereupon deleted ALL the channels I had stored, and as a result, I
can ONLY get DTVs
that have shut down their analog allocations by entering their real
channels.  If I enter
'2', since channel 2 exists, it switches me to '19'.  But with
WFXT-DT, entering '25' gets me
a "NO SIGNAL" message;  entering '31' brings the picture right up.  So
I have this question
for the engineering types...explain to me again how after TV stations
have turned OFF their analog
transmitters, they can still be identified as being on those channels
even though people
using over-the-air TVs will be getting them on the permanent DTV
assignments?
S
I
D
E
B
A
R
Although I can't get WZMY-DT by entering '50', when I enter '35', the
little box on the
upper right-and of the screen first displays '35' then changes it to
'WZMY-DT1 50'.

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