> Sure, a UHF isolator will not protect the transmitter from
> VHF transmitter junk. But isn't the flip side that out of
> band VHF junk is less likely to produce UHF transmitter
> intermod than in band transmitter junk?
Not necessarily. If it were the other way around (UHF coming back down the
hose into a VHF transmitter), the harmonic filter built into the PA would
prevent the VHF energy from getting to the devices.
I had a UHF repeater (GE Mastr II 1/4 kW tube) with a VHF remote base (25
watt Micor mobile). The two antennas were about 20' apart from tip of the
VHF to bottom of the UHF. I had mix problems in the tube PA that produces
products at frequencies that intermod math would never predict to occur when
the remote base Tx was keyed up. Adding a pass cavity to the repeater Tx
cured it.
> And also, while a VHF
> band pass cavity might do its job resisting unwanted in band
> stuff, doesn't this cavity still easily pass undesired junk
> at frequency multiples?
Sometimes yes. A quarter wave cavity will resonate just fine at odd
multiples. The converse isn't true though; a UHF pass cavity will do a good
job of keeping out VHF.
--- Jeff
