1. In North America, the frequency spacing between FM broadcast
transmitters in the same area is usually 800 kHz. 105.3 MHz - 104.7 MHz =
600 kHz. Are you sure about the two FM broadcast frequencies?

Hy,

Yes I`m sure, in EU we have RX feq - 600 KHz for TX on 2m Ham band, for
PMR band it is RX + 4.5 MHz for TX ..


2. IM is produced from a nonlinear response in something. The odds are
strong that the 145.1 MHz signal is being produced in one or more of the
three transmitters - most likely one or both of the FM broadcast
transmitters. Adding filtering in your system will have no effect if the
IM
is produced outside.

I made a spectrum check at RX side after duplexer, there is lot of junk but
145.1 is clear, than I put repater in TX mode with spectrum connected at
duplexer RX port and you can see a modulated carrier - 95 to -90 dbm. In
demodulation mode (Wide) you can hear mixed program of this two
radiostations. I repat this test few times on two different spectrum
analyzers with and WO external attenuators in input line with same results.

I`m sure where is source of IM, repater antenna, coax line, or duplexer?
Maybe all 3-parts togother since duplexer is not Hi.quality, it is made from
aluminium cavity and Cu plunger, no sliver plating, RX and TX side are
separated so there is no good DC connection !


3. It is a good idea to perform a classical IM analysis (up to at least
seventh order) that involves all seven of the broadcast frequencies and to
use the analysis to select a repeater pair that does not involve an IM
frequency.

:-(( very hard, only if we change SHIFT



4. Theoretically, you could place a filter or isolator in the broadcast
transmission lines.

:-))

TNX Mac for all.....