Using 30ft of wire, square, in a Wellbrook ALA100, I get a whopping
120mVpp. It's much higher than I would have guessed. [Yes, the scope
was put in the 50 ohm position.] The signal is dominated by a local BCB
station at 740Khz, with a bit of 810KHz as well. I cranked the time
down way slow to get a fat band on the CRT to check the Vpp. It's the
occasional superpositon of sine waves that makes the vpp so high.

I have a selective level meter that I can try to use some other time to
see the energy at each frequency. I got it in a bid lot years ago (I
wanted something else in the lot), so I don't even know if it works. [I
fact I got two and gave one away to save space!] I'd have to run a
signal generator into it and see if it is trustworthy.

Anyway, that should give you a starting point. It's kind of obvious now
why the 7030 switches in some sort of filter once you go about the BCB
(technically the old US BCB, before it was extended.] The signal levels
above AM BCB must be at least an order of magnitude lower, maybe more.
If BCB is not in your target, I'd suggest a high pass filter before
your amplifier.

Unless you have a spectrum analyzer handy, you might want to consider
getting a selective level meter for your project, if only to very your
measurements.
http://cgi.ebay.com/ws/eBayISAPI.dll...sPageName=WDVW
They don't go for much money since they supply is huge. They were used
in telco years ago but are not required anymore (different technology
or something like that.)