Re: DTV antennas?

On Jul 12, 10:48 am, Jeff Liebermann <je...@xxxxxxxxxx> wrote:
On Fri, 11 Jul 2008 17:18:33 -0700 (PDT), mpm <mpmill...@xxxxxxx>
wrote:

As for the broadcast end of things, the FCC's website does provide
antenna detail.
Manuf, model, height and pattern.   If you're good, you can pretty
easily decode the horiz & vertical, # of bays, and gain of the
antennas just by deciphering the antenna model number...

Yep, but you can't decode it from the FCC data.  The typical Narda
field strength meter:
<http://www.narda-sts.us/products_highfreq_srm.php>
yields the equivalent of a isotropic receive antenna by conglomerating
the various polarizations into a single reading.  That's what's
plotted (and interpolated) on the FCC site.

For example, KFOX in El Paso, TX.
http://www.fcc.gov/fcc-bin/tvq?list=0&facid=33716

Send me your coordinates (or nearby street intersection) and the
channel number you are having trouble with.  I'll be happy to take a
look at it for you.    -mpm

One of the fun things to do is to use the antenna pattern from the FCC
web pile to generate a field strength plot of the area using free
software such as Radio-Mobile:
<http://www.cplus.org/rmw/english1.html>
and the SRTM topo maps.  The FCC does it crudely for "coverage area"
such as this:
<http://www.fcc.gov/fcc-bin/FMTV-service-area?x=DT1092992.html>
It would be rather bad if you were located in a protected null in the
pattern.  I can grind out a sample if you supply the station.

--
Jeff Liebermann     je...@xxxxxxxxxx
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

A Narda meter will read field strength in terms of E or H field, not
power density.
Though I supose if you know enough about the probe, you can do the
conversions...

Also, be advised that for FM at least, the FCC uses a modified
Bullington propagation model which will not consider obstructions (or
water) closer than 3km, and no further away than 16km. So for FM
stations along the front range in Colorado for example, the FCC
patterns will deviate significantly from real world performance. (FCC
plots have more to do with short-spacing and licensing issues, not
coverage.)

The null you're seeing in the FCC pattern (KFOX) is terrain
obstruction. Not an antenna pattern null.
This pattern is typical of all stations on Ranger Peak.

Still, for the purpose of this thread (i.e. poor or no DTV reception),
field is not the issue. Power density is.
The numbers & plots provided on the FCC public website are completely
adequate for determining whether or not you "should" be receiving a
DTV signal at your location.

.

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