On 3/18/2015 3:28 AM, Jeff wrote:

They do not have to be short - but as long as you have a multiple of 1/2
wavelength between the two diplexer inputs, each input will see the very
high impedance of the other input. Rather easy, since you are operating
on the third harmonic.

Don't forget that it is not a simple as being 1/2 wavelength long, you
have to take into account the input impedance of the filer which may
substantially modify what you are looking at, and may load the other
filter affecting its response. The DCI dual band filters are aligned as
a unit so those sort of effect can be taken into account.

Jeff

The input impedance of the filter active filter would be 50 ohms, so no
loading. And the impedance of the other filter would be very high.

I would not expect matching a 50 ohm antenna to a good quality filter
(which these are) would affect their response significantly enough to
cause a problem. After all, this is the exact type of operation they
are designed for.

You *might* be able to measure some effect in a lab, but in the real
world it won't make any difference.

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================