HB9DST wrote:

Past experience at other QTHs tell me that I will also need a
counterpoise. But here's the question: does the counterpoise radiate,
even if it's cut to 1/4 wavelength?

Yes, it will radiate - *especially* if it's cut to a quarter-wavelength.

Then, if I put the counterpoise on the floor in my shack I haven't
really solved the problem because the CP radiates into my shack and my
neighbors' apartments?

I realize that a counterpoise is the "second half" of an antenna. That
being the case, what's the difference between a traditional dipole and
a longwire/counterpoise configuration? Both legs radiate, correct?

Correct. If you call it a "counterpoise" instead of "the second half of
the antenna", it changes nothing but the name. It is still the same
wire, and will radiate exactly the same in both cases.

However much RF current you manage to push into the part of the antenna
that you do want to radiate, you can be sure that an equal current is
flowing into the other part... or maybe into the mains wiring.


--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek