Generally, you should always have some sort of antenna connected, otherwise the radio "sees" an open-circuit, where it should have a 50 ohm impedance load. open circuit means power reflected back into the radio, which potentially cause damage (on very high power radio transmitters with many W output, it does: probably less of an issue on a CM9)
We put together some "dummy antennas" with a 51ohm resistor on an N connector, which terminates the radio into approx the right load, and still radiates (not with any decent beam pattern, but it does) and with two of them placed about 1-2 feet apart, you get enough free space loss to create a "good" RF link. It's pretty repeatable too.
In our experience there are definitely batch yield issues on CM9s, I'm surprised more people don't complain. There are plenty of alternatives, including R52.
Would be great to hear more from other people -
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