Yes, in theory, antennas (not antennae-they're for insecty things) or aerials should be half waves, full waves or multiples, but antenna theory is ruddy complex and for what we're doing, probably not worth it. Just think, at 27MHz, the wavelength is approx 11 metres, so a half-wave dipole would be 5.5 metres long. You're not going to want to be waving that around at the lake, so the antenna is 'loaded' to make it shorter.
Transmitter antenna length is, however, still critical. Get it wrong and, as someone has said, not all the RF energy will be radiated, some will be reflected back into the transmitter, which is undesirable. Yes, ultimately, it could be magic smoke time.
Receiver antenna length is not so critical. For some years, I did my HF radio listening on a 'long wire'. Its length wasn't scientifically calculated, it was simply the length of my garden. It worked quite efficiently on all the HF bands from 1500 metres (BBC) right down to the 10 metre amateur band. However, when I got my Class A ham licence and started to transmit, that was a different matter and a 'proper' antenna was called for.
In short, unless you go silly with the pruning, I think all you'll lose is a bit of range, but not enough to be noticeable for the majority of us.
This is one of 'those' topics, so feel free to ignore me (many do!) or agree, as you see fit!
Andy
G0CCX
