[opendtv] Re: ATSC XMTR/RECV compatibility issue?
- From: "John Willkie" <johnwillkie@xxxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Sun, 18 Feb 2007 17:37:12 -0800
Barry;
I'm singularly unqualified to handle AGC issues with digital; I have to
revert to analog, and there aren't any image or oscillator issues like I'm
accustomed to analyzing.
I do know enough about AGC to suspect that when you are at maximum
sensitivity, things like an about-to-ring Nextel phone can cause
interference. (When I had my Boost Mobile (Nextel prepaid) phone, I could
tell that it was going to ring about 12 seconds in advance because I would
get clicking in the speakers on my computer, even when I wasn't listening to
music.)
So, I resorted to what I 'kinda' know -- transport layer.
Speaking of expensive test/monitoring equipment. Many RF transmission
issues can be diagnosed by a very powerful and deceptively inexpensive
device, the Modulation Sciences 4400a
(http://www.modsci.com/products/televisionProducts/msi4400/index.asp) (I
have no business relationship with Modulation Sciences, but I did see this
device before it was released.)
And "expensive" doesn't mean much. There is much monitoring gear that tests
against the DVB TR 101 290 spec. Which means that the gear is just about
worthless, since there is significant difference between DVB transport
streams and ATSC ones, and 101 290 deals extensively with RF issues.
There is a recently published ATSC Recommended Practice (A/78) that is
ATSC-centric and is more extensive (aside from RF issues) than 101 290. I
don't know of any gear now on the market that tests for A/78 compliance, but
I'm working on finishing one.
I just did a quick check on the Tektronix, Sencore, Harris (Leitch and
Videotek) and Triveni Digital web sites. No hits for A/78. I suspect that
at least one of the above will have an A/78 product or three shown at NAB.
A lawyer would say that a description of having "expensive test equipment"
is a conclusory statement and not of much value. Not a criticism of you;
there is much expensive test equipment that won't help resolve this issue.
John Willkie
> -----Original Message-----
> From: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx]
> On Behalf Of Barry Brown
> Sent: Sunday, February 18, 2007 5:07 PM
> To: opendtv@xxxxxxxxxxxxx
> Subject: [opendtv] Re: ATSC XMTR/RECV compatibility issue?
>
> John,
>
> Thanks for your time and reply.
>
> I don't have many answer to your questions, but will tell you what I
> do know. The problem station is WAVY-DT, the NBC affiliate in
> Norfolk, VA. I live about 35 miles from the transmitter. The CE at
> the station indicates they use very expensive test equipment. I don't
> know if their signal is being continuously being monitored but they
> do say it is compliant.
>
> I haven't noticed any pattern to the dropouts but I will monitor it
> with this in mind and a stopwatch.
>
> You didn't mention anything about my thought this could be AGC
> related. Is this very remote or off-base? The reason why I connected
> this possibility to the problem is knowing the attenuation I'm
> inserting is bringing the tuner very close to maximum sensitivity.
> The image is stable only over a small signal strength range. If I
> increase the attenuation a bit more, the pixillation returns probably
> due to low signal conditions.
>
> I forgot to mention in my original post that I have another ATSC
> tuner that has no difficulty receiving the signal at full strength.
> Both tuners are working off the same antenna being fed through a 2-
> way splitter. This probably will be an answer to some of your other
> questions.
>
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