If you are doing a demo, you need know that there will be some 6m
activity at the right time. In general, I'd guess that 40m might be
more reliable for having signals present.
For a scheduled CW QSO, 6m would work well because the
antennas are reasonably sized. You will need to make sure that
your receiver has enough audio output (or add an external audio
amplifier) so the whole room can hear the QSO.
Probably the simplest receiver to build would be a crystal
controlled direct-conversion. Here are some places to look for
Also, if you just want to demonstrate a CQ QSO, you can do that
by running an audio oscillator into your 2M HT. It demos best if the
station you are talking to is using an oscillator at a different audio
frequency,so the class can tell the difference between what you are
sending and receiving.
good luck ! - Dale WB6BYU