In the immediate vicinity of a transmitting antenna, there are
generally electric and magnetic fields which are not "radio waves"
(electromagnetic fields). If you really want to know the "radio wave"
(electromagnetic field) strength, you should measure it far enough
away from the antenna. Do a Google search for "antenna near field"
for a whole mess of references. The first that popped up for looks
like a good start: https://ewhdbks.mugu.navy.mil/ANTNRFLD.HTM. After
you have an understanding about near and far fields, have a look at
things like http://www.scott-inc.com/html/nist.htm, or other pages you
can find with a search for "NIST standard antenna." You'll also get a
lot of references from an "electromagnetic field measurement" search,
but a lot of them will be for places that will do the measurement for
you, and a lot of the rest will refer to NIST work. The essence is to
measure the voltage developed across a standard antenna placed in the
electromagnetic field you wish to measure. You can either build or
buy a standard antenna for the measurements.

If you only care about relative measurements, like "did it get
stronger after I did this or that," then you can use any old antenna
and simple detector and meter arrangement and just look for changes.

Cheers,
Tom

(Meeker) wrote in message . com...
I am new the world of radio waves, but I am trying to find out if I
can buy a device which will tell me how strong the radio waves are
coming from a large antenna? This is assuming that I am standing
within 10 meters.

I know that a frequency counter tells me which frequencies are being
transmitted. But what tells me how strong they are? Any idea who sells
them?

Any ideas?
Thanks, Meeker