[opendtv] Re: Integrated DTV PSIP

  • From: Doug McDonald <mcdonald@xxxxxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Fri, 02 Dec 2005 10:24:59 -0600

John Shutt wrote:

>>The antenna pointing problem has to be solved even for
>>recording devices. Meaning, not solved with rotors, IMO.
>>In principle, that also applies to the analog time
>>service from PBS. It seems fairly robust, but I'm sure
>>it too has its limits.
> 
> 
> The ideal situation is to be able to use omnidirectional antenna.  Unless 
> you are in a very rare situation where you are way out in the boonies 
> between two major markets and can only receive signals with a huge mast 
> mounted antenna, an omni antenna with preamp if necessary should suffice. 

JOHN: let's be blunt: TALK ABOUT WHAT YOU KNOW ABOUT.

I'm not in the boonies. I'm in the city. We have major stations in
two directions, and soon to be three (now w and ene, soon to be s too).
Despite being in a rather flat area, we do have some topography,
and there are many places in town, including where I live, where
you can get any Fox station with any existing omni antenna. Even
in the best places it's iffy. PERIOD. In the good places it's
perfectly easy to get all stations with a good BI-directional
quad bowtie, such as any commercial one with the reflector
cut off ... but there are NO commercial antennas which will
get all networks reliably in an attic or on a very low
roof, unmodified. What people are using is two antennas with two
downleads. The problem, on a roof or attic, is NOT
MULTIPATH, it is signal strength of the Fox channels.
I know what I speak about, since I have now gone around
with a spectrum analyzer measuring things. Using the two antennas
solution the "wrong antenna" indeed has terrible multipath, but even 
then the newer STBs usually work just fine IF THERE IS PLENTY
OF SIGNAL. But usually, except for one station, when there
is bad multipath, the absolute signal strength is TOO LOW.

Now I suspect that a PROPER omni antenna, mounted well off the
roof, would work fine ... but even the nearest Fox would be a
problem in many places unless it were an 8-bay antenna. AND NOBODY SELLS
EVEN FOUR BAY ALL-UHF BAND OMNI ANTENNAS. I've tried designing such 
things and failed. It's not easy to get them all phased so that
it remains omni over the whole band. We have UHF channels from 18 to
48, soon also a 50, and they will remain after analog turnoff. There is 
also a VHF Ch. 9, but it's close and easy to get.

Now if the closest Fox were on a 1000 foot tower instead of
about 480 feet, things would be mighty different. But it's not.
There are other Fox's available, but they are equally weak,
at best.

And we are NOT "between markets" ... we are fairly close to the
center of ours.

Doug McDonald


 
 
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