[opendtv] Reception range
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 23 Aug 2006 18:49:33 -0400
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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