On 09 Dec 2009 21:07:18 GMT, Ed wrote:

We have 2M packet node transceivers at a new government radio site. The
new site owner requires isolators be installed on all transmitters. As you
might surmise, it doesn't seem possible to do so on a simplex one RF port
radio such an Alinco DR-135.

The isolator has to go between the PA stage, after the low pass
filter, but before the T/R switch. That will require some surgery
inside the radio to bring out two coax cables to the external
isolator.

I'm rather surprised that a government site would allow a DR-135T
radio. While the DR-135T is perfectly suitable for a stand alone
packet radio application, such radios don't do very well in an high RF
polluted environment.

Has anyone done an intermod calculation for all the radios in the
building?

Anyone out there with some realistic suggestions on how we might manage
to do this?
Ed K7AAT

See above. If the site manager is fairly liberal, you might be able
to convince him that a simple bandpass cavity will suffice. It should
work because your packet box is running simplex. Even if he demands
an isolator, you still should have some manner of cavity BPF in the
line. I don't mean a little tiny soda can size cavity, but rather
something larger, with skirts that are way down. See cavity on the
left:
http://www.LearnByDestroying.com/k6bj/K6BJ%20Repeater/slides/2m%20rx%20cavity.html

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