Fred McKenzie wrote:
If I only have room for a short dipole, say 40 feet, and use a tuner such
as the SGC or Icom AH-4, what is the penalty in DB for the lower bands
(160, 75, 60, 40) compared to a half wave on each band?

Don't know the dB but losses would be appreciable. Why not
put up a 22 foot vertical with a good radial system? That
will work pretty well for 40m-10m using the autotuner at
the base. Install a base loading coil and it will work
reasonably well on 75m. Can't say much for 160m.
--
73, Cecil, http://www.qsl.net/w5dxp