[opendtv] Re: ATSC Test system - cheap

channel edges need to be explained?  You probably need to ask Les in detail,
since we just talk shorthand when we've discussed this.

As you no doubt know, to make 8-VSB work in the real world, the exciter
needs to suppress out-of-band emissions, and these are tightly regulated by
the FCC to minimize interference between adjacent channel stations.  Good
filters are expensive, and the terrestrial RF environment is quite dynamic,
in the sense that stations are not co-located.

The teleview modulator doesn't have filters good enough to suppress adjacent
channel emissions and round off the channel edges in a terrestrial
environment.  For cable and single-channel testing applicaitons, however, it
works well.  Cable systems use fized power, and each effectively uses the
same transmitter location, so the environment is much less dynamic.  And,
much less Gaussian and Rayleighian interference, so to speak.

Amateur regulation is roughly equivalent to LPTV regulation.  In the analog
world, full service tv stations have each sub-element (audio, video,
subcarriers) regulated by the FCC.  For LPTV, stations are just regulated by
their RF envelope.  For example, I know of an LA based LPTV on channel 6.
They're using it to broadcast an FM station -- with occaisional video -- on
87.75 Mhz.  It even lights up stereo lights on FM sets.  One couldn't even
dream of doing that with a full service station.

Since there are no fixed channel assignments in amateur service,
particularly those 6 mhz apart from commercial operators, I suspect you'd
have few to no issues with using the Teleview modulator in an amateur
environment -- it's for experimentation, after all.

John Willkie

----- Original Message ----- 
From: "Ron Economos" <k6mpg@xxxxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Sunday, July 24, 2005 5:22 PM
Subject: [opendtv] Re: ATSC Test system - cheap


> Can you tell us what an "edge" issue is? I've been toying
> with the idea of using one is these modulators for amateur
> radio DTV experiments in the 420-450 MHz band (the
> vogue is to use cable channel 58 at 427.25 MHz, so that
> a cable ready TV can be used as a receiver).
>
> For amateur applications, spectral purity, bandwidth and
> stability are not strictly regulated. Basically, you just have
> to keep your modulation sidebands within the 420 to 450
> MHz band.
>
> Ron
>
> John Willkie wrote:
>
> >be warned:  while the 8-VSB modulator works well -- I've known people who
> >have used them extensively for testing and cable uses -- it is not stable
> >enough for broadcast use.  IIRC, that's because of 'edge' issues.
> >
> >John Willkie
> >----- Original Message ----- 
> >From: "Ron Economos" <k6mpg@xxxxxxxxxxx>
> >To: <opendtv@xxxxxxxxxxxxx>
> >Sent: Friday, July 22, 2005 2:17 PM
> >Subject: [opendtv] Re: ATSC Test system - cheap
> >
> >
> >
> >
>
>>http://www.computermodules.com/broadcast/rf-8VSB-modulator-QPSK-Quam.shtml
> >>
> >>
> >>
> >>
>
>http://www.computermodules.com/broadcast-systems/professional-8VSB-modulato
r.shtml
> >
> >
> >>Ron
> >>
> >>Craig Birkmaier wrote:
> >>
> >>
> >>
> >>>I have received a message from a friend of a friend who needs help
> >>>generating ATSC test streams to test various ATSC "decoders"
> >>>(receivers). Here is the request:
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>>   This is a bit of a reverse from the normal situation, but I
> >>>>hoped some folks here might have some ideas.
> >>>>
> >>>>   I'm looking for ways to easily test and compare ATSC decoders.
> >>>>I'm looking for a PCI card or something that can take a local
> >>>>ATSC-compatible .ts file, and mux it and sent it out over coax, to
> >>>>which I can attach a normal ATSC decoder, which would see it like it
> >>>>was an antenna. Just like how VCRs used to work - RF out over coax,
> >>>>pretending to be channel 3 or 4.
> >>>>
> >>>>   I've seen some very high end systems that do a huge amount of
> >>>>stuff I don't care about. I'm looking for something simple and
> >>>>inexpensive - hopefully cheap enough that the company would actually
> >>>>publish the price :).
> >>>>
> >>>>
> >>>>
> >>>>
> >>>I remember a recent story about a PC card that may be able to do
> >>>this. Does anyone know the specifics, or any other way to do this?
> >>>
> >>>Regards
> >>>Craig
> >>>
> >>>
>
>
>
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