Nigel

You don't NEED dishes - Hams would probably use 'Yagi' antennas for many of the frequency bands used - dishes up to 30 metres wide can be a bit unwieldy! :-) Google it....
http://en.wikipedia.org/wiki/Yagi_antenna

There are many other weirdly shaped directional antenna - but all that is of little real interest in this thread... :-)

You are correct in your guesses about traffic on certain wi-fi channels and it being intermittent. The guy was right AT THE TIME HE DID THE MEASUREMENTS, but life goes on... :-)

Glad you found your old book!