[opendtv] Re: Analog v Digital TV
- From: "John Willkie" <johnwillkie@xxxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Mon, 15 Jan 2007 12:32:28 -0800
That's why I asked. The 8-VSB signal envelope is rather smooth compared to
some digital transmission schemes (like that used in Nextel phones, for just
one.)
For such a spike to enter the transmission system, the exciter would have to
be behaving very badly, and the vestigal sideband filter would have to be
way out of whack.
That's why I went to power regulation. After the exciter/vestigal sideband
filter, there's the power amplifier(s) where a power spike just might be
able to get through.
However, such spikes would drive up power bills, could cause arcing or
flashing and premature aging of the transmission line, and might cause
momentary interference with co-channel and adjacent channel stations.
Last week, I read somewhat skeptically, reports that an A-VSB demo using a
Sinclair station in Las Vegas didn't work right because of "power supply
problems" at the transmitter. To me, that sounded the least likely
explanation. Power regulation in transmitters was something that was
largely solved before I graduated from high school a few decades back.
One dirty little secret is that encoders and multiplexers (the devices that
take in video, audio and data streams and output the transport stream to the
exciter) are often the culprit in these types of situations. However,
encoder issues are unlikely to be fixed by adding a pad to the antenna input
on the receive side.
John Willkie
_____
From: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx] On
Behalf Of Barry Brown
Sent: Monday, January 15, 2007 12:09 PM
To: opendtv@xxxxxxxxxxxxx
Subject: [opendtv] Re: Analog v Digital TV
This may be the wrong term to use, but I'm talking about transition errors
in the digital waveform that might upset the normal operation of the
decoder.
On Jan 15, 2007, at 2:34 PM, John Willkie wrote:
What is a pulse spike?
John Willkie
_____
From: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx] On
Behalf Of Barry Brown
Sent: Monday, January 15, 2007 10:41 AM
To: <mailto:opendtv@xxxxxxxxxxxxx> opendtv@xxxxxxxxxxxxx
Subject: [opendtv] Re: Analog v Digital TV
I wasn't talking about power spikes but rather pulse spikes. Remember, the
Dish receiver needs 21 dB of attenuation to work with this signal, the Mits
doesn't.
On Jan 15, 2007, at 1:24 PM, John Willkie wrote:
Power spikes/dips at the station are rare, but possible. Flashing or other
problems between the transmitter power output and the antenna are also
possible. However, dips are likely to affect all receivers just about the
same, since data would be missing.
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