(Another rocket-denzien, having spectrum analyser, scope, and picmaster :)


>PROBLEM:
>
>I have managed to transmit data down a wire between the units.
>However, I am struggling to do it via the RF link. When the RF unit is
>powered up, the output data pins from the decoder all go high from an
>initial low state. This shows that the RF has been picked up but the
>data is wrong. When I listen to the audio output from the RX, the
>tones cease abruptly when the TX is powered.

What tones?   Can you give more detail on how these rf links are working?
AM/FM?

Beware of having them too close. Ideally, take the TX output into a dummy
load.
You should be able to still rx it from many meters away, and that will
eliminate
any squirrely RF problems from RF getting into the rest of the system.

>I have ground planed the
>circuits from a single point to avoid current loops and have minimal
>lengths of unscreened RF wiring. To get the RF link working at all I
>had to use a pull up resistor on the data output pin from the decoder
>(4k7).


I've got some MING units here that have O/C  outputs. that may be normal
on yours as well.