"http://CBC.am/" wrote:

Where are the DX hdtv recivers?

HD signals do propagate outside their intended markets, to the delight of
DXers.
Yet no one has created a ASTC DX reciver.

To verify DX, all you need is some slow speed data -- and maybe some CC
captions.

There is no slow speed data in an ATSC signal. Verifying that an
8VSB/ATSC signal is present is easy: just look for the carrier
at the assigned frequency. This differs from an NTSC signal
in teh same channel. You could also use an autocorrelator and
look for the 511 bit PN sequence. But there is no way to do anything
more without getting the whole bitstream.

Doug McDonald

"http://CBC.am/" wrote:

Where are the DX hdtv recivers?



I should add that some DTV receivers, certainly the Samsung T-151,
will give you an indication that an ATSC signal is there
at a far lower C/N than is needed to decode it:

1) the green light will blink if you key in the channel

2) if you do a channel scan, it will pause several seconds
at any channel where an ATSC signal is present even if
it it too weak.

One more test: you can also design a circuit that will sync
onto the 5.375 mHz symbol clock in the demodulated baseband signal,
or even in the IF signal, at far less than the C/N needed to decode
it, but not as low as just seeing the carrier. This is of course
useful in doing an autocorellation, or a cross corellation with the
known 511 PN sequence.

Doug McDonald

Doug Smith W9WI wrote:


I suppose you could design a receiver to decode only the PMT (Program
Map Table). This table contains the name the station has assigned to
each virtual channel. At many stations this name is, or includes, the
FCC-assigned call letters. At others, it may contain a slogan that
includes the station's analog channel number and may conclusively
identify the station.

This table is relatively small (compared to enough I and P frames to
build a picture, especially a picture that includes any identifying
information!) so it might decode more easily than the signal itself.

Computer code to decode everything is readily available free from the
Gnu project. You just need to feed it the baseband signal through
a suitably fast PC ADC card.



DXers using the Hauppauge WinTV-D card have noted that these "text IDs"
can be decoded with a signal that's too weak and/or interference-laden
to yield intelligible audio/video. For example, the only verified
reception of DTV via sporadic-E involved decoding of KOTA-DT's PMT. No
intelligible audio or video was received.

Some commercial boxes also can get channel mappings (which can
help identify a station) well before they lock onto the MPEG.



As Doug McDonald suggests, you can detect the *presence* of a DTV signal
by looking for the carrier. It's 310KHz above the bottom of the channel
- for example, 476.31MHz for a DTV station on channel 15. Unfortunately
you can't tell *which* DTV station you're receiving the carrier from...


Is that clear, or are there frequency offsets that can be used?




[0] I realize Europe is using a different DTV standard. It seems to me
the level of difficulty in getting a small transmitter to work is
independent of the 8VSB/COFDM issue.
--

Yes. A transmitter is easier than a receiver. You just need to
feed it the MPEG encoded stuff, which is the same in Europe or
the US (except of course the vertical frequency).

Doug McDonald

Doug McDonald wrote:
As Doug McDonald suggests, you can detect the *presence* of a DTV signal
by looking for the carrier. It's 310KHz above the bottom of the channel
- for example, 476.31MHz for a DTV station on channel 15. Unfortunately
you can't tell *which* DTV station you're receiving the carrier from...

Is that clear, or are there frequency offsets that can be used?

A limited number of channel allocations are marked with "c" in the
table. This requires their carrier to be offset by some specific value
(with five significant figures which I can't remember...) from an
adjacent-channel analog station. I would suppose that means their
carriers may be 300 or 320KHz up depending on the offset of the analog
station.

There are very few such allocations - none here in the Nashville area.

Yes. A transmitter is easier than a receiver. You just need to
feed it the MPEG encoded stuff, which is the same in Europe or
the US (except of course the vertical frequency).

Their designs included the MPEG encoder.
http://www.von-info.ch/hb9afo/datv_e.htm
http://www.datv-agaf.de/
(latter site mostly in German. It indicates they're selling the cards
for amateur applications for "slightly higher costs" than 750 euros.
(roughly equivalent to $750))

If I read things properly - and I may not - these cards are capable of
generating an ATSC-compatible 8VSB signal from an analog NTSC input.
Probably no PSIP though which could be a problem with most receivers.

They're using satellite receivers, sometimes with preamps attached, for
their receivers.
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com

"http://CBC.am/" wrote in message
...
Where are the DX hdtv recivers?

HD signals do propagate outside their intended markets, to the delight of
DXers.
Yet no one has created a ASTC DX reciver.

Any ATSC receiver can pick up DX. All you need sometimes is a set of rabbit
ears to pick up DTV stations up to 100 miles away. At least that's what
some guy in New York City got when he received a Philadelphia station.

Drewdawg wrote:


Any ATSC receiver can pick up DX. All you need sometimes is a set of rabbit
ears to pick up DTV stations up to 100 miles away. At least that's what
some guy in New York City got when he received a Philadelphia station.

Yep, very true indeed. Last summer I ROUTINELY watched
WRTV (Ch 25) in Indy from 108 miles away. But ... it's a maximized
power station on a tall tower, and there is the very wide
Wabash valley right where the earth's crest is.

The other Indy stations are much more rarely visible,
and, surprise surprise, I've never seen the one I really
want, Channel 9 (CBS).

Doug McDonald

Doug McDonald wrote:

Drewdawg wrote:


Any ATSC receiver can pick up DX. All you need sometimes is a set of rabbit
ears to pick up DTV stations up to 100 miles away. At least that's what
some guy in New York City got when he received a Philadelphia station.

Yep, very true indeed. Last summer I ROUTINELY watched
WRTV (Ch 25) in Indy from 108 miles away. But ... it's a maximized
power station on a tall tower, and there is the very wide
Wabash valley right where the earth's crest is.

The other Indy stations are much more rarely visible,
and, surprise surprise, I've never seen the one I really
want, Channel 9 (CBS).

One item of note: I live on the east side of Indy, significantly
farther than 10miles from the antenna farm. Channel 9 is BY FAR
the easiest of the 5-6 (or more) DTV channels for me to receive.

The simple indoor rabbit ears for myi Hi-VHF reception seem to require
no augmentation for optimum performance (while the reception of the
UHF stations is either slightly or significantly more problematical.)
Luckily, Ch9 isn't being starved by using a 2kW or other nonsensical
power level. Frankly, if the transmitter was 100kW or somesuch, it
would be incredibly fantastically easy to receive :-).

Note: my current set-up does indeed use a preamp on the dipole,
but because of the diplexer that I use to combine with the UHF
reception, and I only use a 13dB gain (good quality) preamp to
mitigate the subsequent losses.

Ch9 was the first signal that I received with my DTC100 survey receiver,
and it was almost impossible to fail to receive.

It is amazing for a 19kW transmitter, that the signal is easy to
receive. However, the relatively lower frequency and high true
gain of simple dipoles at the Ch9 frequency seems to help. (I
know that you know this, but others might not realize: It
is easy to be seduced by the 'high gain' of UHF antenna designs,
but non-RF types need to understand that the gain is specified
relative to an isotopic or dipole -- and at high frequencies, the
gathering capability of such antennas is significantly reduced,
because of the smaller area.)

Ch8/Ch9 is (by far) the best source for HDTV in Indy, but the
other stations are getting better.

John

John Dyson wrote:
eceive.

It is amazing for a 19kW transmitter, that the signal is easy to
receive. However, the relatively lower frequency and high true
gain of simple dipoles at the Ch9 frequency seems to help. (I
know that you know this, but others might not realize: It
is easy to be seduced by the 'high gain' of UHF antenna designs,
but non-RF types need to understand that the gain is specified
relative to an isotopic or dipole -- and at high frequencies, the
gathering capability of such antennas is significantly reduced,
because of the smaller area.)

Ch8/Ch9 is (by far) the best source for HDTV in Indy, but the
other stations are getting better.


It's not the best for us in the far field, however.

This is because its extremely easy for us to get an
antenna with huge gain on the UHF channels, one that
is about the same size as a Ch. 9 dipole. To get the
same gain with Ch. 9 requires the same design antenna,
hence a truly gigantic one. If it were 1 MW or even 316 kW,
it would be easy.

Doug McDonald