"J M Noeding" wrote in message
...
......
You seldom see such large dimensions, believe they had
waveguide for the over hoizon radio link system on 900MHz, but usually
WG is not practical below 3.3GHz .......

Nonsense, rectangular waveguide is used quite frequently in UHF television
broadcast transmitting installations. Granted it's pretty good sized stuff
to get the lower cutoff frequency down where it needs to be in the 450 - 800
MHz range (WR1150, WR1500, and WR1800 for example) .. at least 6" x 12"
outside dimensions. But it's definitely practical at those frequencies
which are far below 3.3 Ghz.

See http://www.dielectric.com/broadcast/...rWaveguide.pdf
for full details.

73s