> Again, the circulator will produce intermod when external strong
> signals enter the antenna port when used as a switch for the duplexer
> and there is transmitter power also going through it. 50 Watts or
> 47dBm to -116dBm receiver sensitivity is 163dBm dynamic range. The
> device is not linear enough to prevent detectable IM when strong
> signals are received that are of the correct frequencies to cause IM
> to a receiver.
Which was why I was reluctant to go along with the idea of feeding a
receiver off the third port, or even worse, passing multiple high-level
signals through a common circulator.
Have you ever quantified IMD in a run-of-the-mill VHF/UHF ferrite circulator
before Harold? When I get some time, I plan on trying to do that. I figure
I'll use a high-quality pass/reject duplexer with > 100 dB of isolation as a
two-transmitter combiner, and feed the output to a circulator with the
remaining two ports terminated properly, and measure the third-order
products at both terminated ports. I'll also be curious to see at what rate
the IM products increase as you start to approach (or even exceed) the
isolator's power-handling rating.
--- Jeff
