[BC] Unlicensed operation

[Ron Castro]

You should read the archives this list in June where we hashed this to 
death.  The number for an isotropic radiator is IIRC 18.75 nano-watts. 
That's about .00001875 milli-watts or .01875 micro-watts. For a 
"conventional 32" whip", assumably with a ground system and properly 
matched, the power to the antenna would be limited to about 2.15 dB less 
than that to deliver 250 uV/m at 3 meters.  All the formulas and 
calculations are the thread.  The biggest problem is being able to measure 
a TPO that small, however it can be done with a spectrum analyzer, or with 
a power meter that was described in QST last month that measures signals 
down to something like -70 dBm.

Don't believe everything you read on the Ramsey website!

See below for an excerpt of the thread.

Ron Castro
Chief Technical Officer
Results Radio, LLC

         Re: [BC] FM and AM/Slight drift
      From: Harold Hallikainen <harold at hallikainen.com>
      To: Broadcast Radio Mailing List <broadcast at radiolists.net>
      Reply-To: Broadcast Radio Mailing List <broadcast at radiolists.net>
      Date: Jun 6 2005 - 1:07pm



Back in 1993, I wrote " Unlicensed operation in the FM band is limited to
a field strength of 250 microvolts per meter measured 3 meters from the
antenna. This works out to 165.8 picowatts per square meter, which would
be 18.7 nanowatts into an isotropic radiator." I hope my calculations were
right. I did a V^2/R with V being the field strength and R being the
characteristic impedance of free space (or whatever it's called) to get
watts per square meter. Then multiplied this W/M^2 by the surface area of
a 3 meter radius sphere. Assuming the methodology is correct, it's
something like:

((250uV/m)^2)/377 ohms = 165.78e-12 W/m^2

The area of the sphere is 4*pi*r^2 = 113.1 m^2

So, the power radiated would be (165e-12 W/M^2) * 113.1 m^2 = 18.75nW

At least that's what I get...

You can also point to 15.201
http://www.hallikainen.com/FccRules/2005/15/201/

(b) Except as otherwise exempted in paragraph (c) of this section and
in Sec. 15.23 of this part, all intentional radiators operating under the
provisions of this part shall be certificated by the Commission
pursuant to the procedures in subpart J of part 2 of this chapter
prior to marketing.

Harold


>As long as I have all this brain power here:
>
>On the FM band, Part 15.239 limits the signal strength to 250
>microvolts/meter at 3 meters. What does this translate into an isotropic
>antenna input power? I would like to be able to shut down the argument
>about being allowed 100 milliwatts on the FM band (I know 100 milliwatts
>into 10 feet on antenna and ground IS allowed for the AM band).
>
>I've heard different numbers from 25 milliwatts down to 50 microwatts.
>
>
>tom bosscher