[opendtv] Re: Reception range

The FCC stipulates the Longley-Rice Irregular Terrain Model (LR-ITM), which is 
available as a free dowload:
http://flattop.its.bldrdoc.gov/itm.html
But the HMI is still living in the '70's....
Guidelines for using LR-ITM are found in FCC OET-69 (Feb2004 edition):
 
http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet69/oet69.pdf#search=%22fcc%20oet69%22
 It is a STATISTICAL model, based on AVERAGED statistics for a large number of 
(mostly rural/sub-urban) locations and environmental conditions in the world, 
presuming an outdoor antenna at 10 meter height.  A Clutter Loss correction was 
experimentally found to be needed, esp for urban environments.

The antennaweb.org website uses LR-ITM, but I have been unable to obtain any 
information on HOW they use it, but I believe that they are including 
co-channel and adjacent channel interference effects.
 
The SPLAT implemention of LR-ITM, with a modern graphic interface, is available 
as a free download for LINUX operating systems:
http://www.qsl.net/kd2bd/splat.html

The RADIO MOBILE implementation of LR-ITM, with a modern graphic interface, is 
available as a free download for Windows op sys:
http://www.cplus.org/rmw/english1.html
However, the clutter loss model is inadequate and does not readily support 
input of local parameters, such as indoor/attic loss, sensitivity loss due to 
antenna VSWR and system noise figure calculation.  It is also difficult to 
define a multiplicity of different TX and RX antenna gain patterns and to 
calculate co-channel and adjacent channel interference effects.

I've been using R-M for over a year to estimate UHF DTV performance, esp. 
compared to the generally over-optimistic antennaweb.org:
http://hdtv.forsandiego.com/messages/4364/4900.html?1135634429
I developed an Excel spread sheet calcuator to compare antennaweb.org and R-M 
predictions to actual performance.  The attached update to the (unavailable 
archived) file now includes an Overload calculator for alternative Preamps.

As you will quickly see, many line items in the calculation require making some 
shaky assumptions and tailoring to your specific location...such as FCC's 
recommendation to assume 7 dB for clutter loss irrespective of your local 
terrain/buildings....commercial propagation prediction programs use proprietary 
clutter databases for improved results.

Some of the factors that I know are NOT YET included in the calculation are 1) 
TX antenna elevation gain/loss, 2) close range (under 5 miles) TX antenna gain 
irregularities causing equallizer degradation (see Bob Chase's posts in 
avsforum antenna thread), 3) receiver sensitivity degradation due to intermod 
products and 4) multipath causing constructive and destructive interference 
that is different for each frequency in both horizontal and vertical dimensions.

This latter effect can cause some channels to be received reliably and others 
not at all:
http://www.hdtvprimer.com/ANTENNAS/siting.html

holl_ands
 
========================================
"Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx> wrote: This handy site 
provides the specifics of TV station transmitters:
location, HAAT, ERP, current and planned configurations.

http://www.fcc.gov/mb/video/tvq.html

Enter the call sign and ask for the detailed output. Or enter your
coordinates and a radius, and it will spit out all stations in that
area.

This site says whether a station is still operating under a special
temporary authority.

http://www.fcc.gov/mb/video/files/dtvstas.html

I wanted to see what marginal reception translates to for me, in terms
of received signal strength.

The most marginal station I receive is WBAL-DT (NBC 11 Baltimore). It
operates over Ch 59, at 513 KW ERP, antenna 1023.6' HAAT. Decent output,
decent antenna height.

Using free space propagation, and the measured 15 dB margin I need for
reception, total channel loss should be 142.3 dB, and signal strength at
the receiver, assuming unity gain receive antenna, -55.2 dBm.

Not so impressive. Should come in strong.

Using the Hata model, which takes into account antenna heights as well
as clutter, and feeding in minimal clutter, distance, exact freq, etc.,
I get a total 160 dB channel loss and a received strength of -73 dBm.

The marginal reception makes a little more sense now, but I would think
I'd get solid reception more frequently.

ABC 2, 602 KW vs the 513 for NBC 11, so just slightly higher power, over
Ch 52, comes in much more reliably. Although not very strong in the
signal meter, the difference translates to solid reception most of the
time.

The surprise was one of Mark Aiken's stations. WBFF-DT, operating on a
temporary authority at 46.6 KW ERP, or so the FCC says (as of 13 July
2006), 1223' antenna HAAT, comes in solid. The Hata model claims I
should see about -80.3 dBm at the receiver. Even free space loss would
result in -64.7 dBm. So this should be a pretty weak signal, yet it
beats WBAL, for some reason. And this is determined over the long haul.
Same behavior consistently, since Christmas 2005. Is the FCC wrong about
the STA?

Another data point is WMPT (PBS 22 Annapolis). It shows marginal in the
signal strength meter, though reception is consistently solid. Antenna
is 948' HAAT, at 150 KW ERP, works out to 140 dB path loss with the Hata
model, or total 155 dB loss with the required 15 dB margin. Received
signal strength comes out to -73.2 dBm.

As a comparison, the analog version of WMPT is 5 MW. It's a good analog
signal, but obviously not the equal of 150 KW WMPT-DT in terms of image
and sound.

So aside from whatever magic Mark Aitken is working, looks like -73 dBm,
or slightly lower than that, is what I can expect for marginal
reception.

My antenna should provide several dB of gain, but my low elevation
doesn't help. Also, the antenna aim should be no better for WBFF-DT than
for the other Baltimore stations. So this is a bit of a puzzle.

Bert
 
 
                
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