I have been doing some FM DXing lately, and have been trying to come
up with some "number" to give a relative value to what I have heard.
I know that I cannot look at just transmitter power and distance,
because the transmitter's HAAT has a definite bearing (pardon the
pun...not a reference to a directional antenna). Do any of you know
of a website (or anything else) that can clearly specify the important
criteria for this kind of evaluation, and maybe supply equations as
well?

I have studied the FCC "FM Curves" and other information they have
posted, and the closest thing I can find is a page that specifies the
maximum ERP for a station given the class of a station and the antenna
HAAT. I don't honestly know if anything that I can derive from that
would be directly applicable to what I'm trying to do. I also may
have my head firmly lodged somewhere thinking that this can be done
too. Advice and suggestions gladly accepted.

"Senor Couchwarmer" wrote in message
...
I have been doing some FM DXing lately, and have been trying to come
up with some "number" to give a relative value to what I have heard.
I know that I cannot look at just transmitter power and distance,
because the transmitter's HAAT has a definite bearing (pardon the
pun...not a reference to a directional antenna). Do any of you know
of a website (or anything else) that can clearly specify the
important
criteria for this kind of evaluation, and maybe supply equations as
well?

I have studied the FCC "FM Curves" and other information they have
posted, and the closest thing I can find is a page that specifies
the
maximum ERP for a station given the class of a station and the
antenna
HAAT. I don't honestly know if anything that I can derive from that
would be directly applicable to what I'm trying to do. I also may
have my head firmly lodged somewhere thinking that this can be done
too. Advice and suggestions gladly accepted.

Are you trying to evaluate how far beyond their normal coverage you
are hearing a station? If so, the FCC has a contour plot for every FM
station on their FM Query. The plot is for the 1 mV/m contour for all
stations except Class B, where it is the 500 uV/m contour. These are
the protected contours. These field strengths are those predicted for
a receiving antenna 30 ft above ground. Coverage depends very strongly
on terrain.

Doug Vernier's Am Fm by ZIP Code web site
http://www.v-soft.com/ZipSignal/zip_answer.asp
gives predicted field strength for every ZIP code down to signals well
outside their protected contour. He's in the coverage prediction
business so I'd trust his data. Of course it is meaningless within
the same ZIP code as the transmitter.

"Robert J Carpenter" wrote:


"Senor Couchwarmer" wrote in message
...
I have been doing some FM DXing lately, and have been trying to come
up with some "number" to give a relative value to what I have heard.
I know that I cannot look at just transmitter power and distance,
because the transmitter's HAAT has a definite bearing (pardon the
pun...not a reference to a directional antenna). Do any of you know
of a website (or anything else) that can clearly specify the
important
criteria for this kind of evaluation, and maybe supply equations as
well?

I have studied the FCC "FM Curves" and other information they have
posted, and the closest thing I can find is a page that specifies
the
maximum ERP for a station given the class of a station and the
antenna
HAAT. I don't honestly know if anything that I can derive from that
would be directly applicable to what I'm trying to do. I also may
have my head firmly lodged somewhere thinking that this can be done
too. Advice and suggestions gladly accepted.

Are you trying to evaluate how far beyond their normal coverage you
are hearing a station? If so, the FCC has a contour plot for every FM
station on their FM Query. The plot is for the 1 mV/m contour for all
stations except Class B, where it is the 500 uV/m contour. These are
the protected contours. These field strengths are those predicted for
a receiving antenna 30 ft above ground. Coverage depends very strongly
on terrain.

Doug Vernier's Am Fm by ZIP Code web site
http://www.v-soft.com/ZipSignal/zip_answer.asp
gives predicted field strength for every ZIP code down to signals well
outside their protected contour. He's in the coverage prediction
business so I'd trust his data. Of course it is meaningless within
the same ZIP code as the transmitter.


I am trying to evaluate all stations heard on FM. For ones that are
local or semi-local, its more an exercise in statistics than anything,
because they can't be construed as a "catch" unless its on a home-made
radio (and even then maybe not). For non-locals, its to assign a
"degree of difficulty" for lack of a better phrase. Also to try to
establish a reason why a 400-watt station at 60 miles out with a high
HAAT value is received much stronger than a 68KW station at 115 miles
out with a slightly lower HAAT. Both have mountain-top transmitters
and are non-directional. I'm also trying to figure out how to
evaluate stations received during skip, but considering that each
episode of skip is probably unique, only catches made during the same
episode could be evaluated (if at all).

The contour plots would be a good reference for locals and
semi-locals. The "degree of difficulty" that I am trying to figure
out would be a mathematical extension of the contour plots for the
area beyond the plot. I'm banging my head against the wall here
looking for words, and just referred back to the web site you
mentioned. I picked one station which according to the list for my
zip code delivers 65.1DBu to the area. That transmitter is 70.2km
away. There is a range of hills between me and that station. I
picked a zip code on the other side of the hills that is about 25km
closer, and the signal strength there is 76.4DBu. If I were 150km
distant, it would deliver much less than 65.1DBu, but how much less?

With regard to Doug Vernier's web site, I have trouble believing it.
Either his data is based on some very old information, or I live in a
zip code that's a complete anomaly. He lists 143 stations for my zip
code. In order of descending signal strength, #28 is an FM station
that is completely inaudible because the frequency is completely
covered by another station that doesn't even make his list. #43
should be in the top 5. #13 should probably be #2, #22 breaks up so
badly at night that it is virtually inaudible, and he is listing their
night pattern as #22. I don't think its my specific location within
the zip code, I think its the data. I also don't think that the
theoretical data he is using takes into consideration adjacent channel
interference at all. I could be wrong, but I'll trust my ears on this
one.

Anyway...time for coffee. Am I on a tangent here?