As you make the antenna longer in relation to a 1/4 wave, two things happen.
The 234/FMHz is the formula for a 1/4 wave antenna. This is not all that
accurate, nor does it need to be, for VHF and up. At 800 MHz the diameter of
the antenna has a large effect. For receiving purposes it really isn't all
that critical. The fatter the antenna, the better would be a reasonable rule
of thumb for VHF and up receiving. If your interested, I can give you the
formuli for determining the K-factor. (How much to shorten an antennas as it
becomes larger in diameter)

Line of sight transmissions are either there or there not, a better antenna
will decrease noise on a week station, but the greatest antenna ever built
will not pull in an out of range signal.

1. the impedance changes - this may require a matching system between the
antenna and the receiver for maximum efficiency.

2. The angle of elevation changes, for example a very long vertical in
relationship to frequency would work well only straight up! (assuming
vertical polarization.)

All antennas are compromises, for local line of site to the horizon (VHF
reception and higher multidirectional) it is tough to beat a 1/4 wave cut
for the particular band and sloping radials to increase the impedance.

"Rich B." wrote in message
...
Sorry post was too short there!
Does the factor of 234 equal a full wave or partial wave like 1/4? 3.3"
sounds shorter than I'm used to seeing. Is there any reason, other than
the
result being too tall of a device, to use an antenna that is not a full
wave?
Or to put it another way, if I build a di-pole ant. for 850 mhz what part
of
a wave length will result in the best reception? Would there be any harm
in
tuning for 2 wave lengths? See where that question is headed, if 2 is OK
then it will work on another freq as a 1(full) wave length antenna.
I seem to remember that 850 mhz was full wave at 13.8" so a half wave for
425 mhz is 13.8" too, is this right?