[opendtv] Re: ATSC XMTR/RECV compatibility issue?
- From: Barry Brown <barrysb@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Mon, 19 Feb 2007 07:07:59 -0500
Thanks for the tip, tried it, but no joy.
Barry
On Feb 18, 2007, at 8:17 PM, Ron Economos wrote:
The signals do not have to be in-band to cause
overload. Typically, the most powerful signals
present at the input of any receiver are from
FM broadcast transmitters at 88 to 108 MHz
and paging transmitters at around 150 MHz.
I would try an FM trap. It's an inexpensive
experiment.
http://www.warrenelectronics.com/Antennas/Att1.htm
Ron
Barry Brown wrote:
After spending more than a month trying to work out an ATSC
reception problem I've been having with one of my local stations,
I'm beginning to wonder if there isn't some uncovered
compatibility problem between some ATSC transmitters and tuners.
I'm hoping someone on this list familiar with the technology can
provide some information concerning the problem.
I posted here about a month ago, indicating the reception of the
problem station was unstable, continuous pixillation, stuttering
sound, picture freezes, and error message reports indicating "Loss
of Signal". I also reported that this was not an overload
condition as the station is not the strongest in my area. Also,
it didn't appear due to multipath errors as the images from
analog stations nearby the transmitting frequency of the DTV
station were ghost free. I reported that inserting a large amount
of attenuation in the antenna feed did, in fact, stabilize the
receiver.
Knowing I was probably hiding the problem rather than fixing it,
I began thinking that what I was doing when inserting the large
amount of attenuation was actually forcing the receiver to work
at its highest possible sensitivity and thereby effectively
eliminating the affect of AGC controlling the RF-IF amplifiers. I
researched this possibility a bit and found that ATSC does have a
coherent AGC system. I theorized if there was some signal
impairment in the transmitted signal, it might cause the AGC of a
improperly designed receiver to become unstable.
I contacted the Director of Engineering at the station, who
happens be responsible for at least two area DTV stations, one of
which I receive without any problem and told him of my concerns.
He related he saw no difference in the transmitted signals from
both of these stations using his standard monitoring equipment.
My questions are:
1. Does my thinking seem reasonable?
2. If so, what type of signal impairment might cause the local AGC
to be unstable?
3. What procedure should be used to visualize then correct the
problem at the transmitter, or
4. What receiver modifications can be implemented to stabilize the
AGC?
BTW, this is not an isolated case. My problem receiver is a Dish
Vip622 and many of them are having similar problems in various
parts of the country but it seems always with only one station in
the market.
Will appreciate whatever input you can give to help resolve this
problem.
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