Separation of RF board and microcontroller board caused problems

From: Dummy (ahkit1021_at_yahoo.com)
Date: 09/01/04 

Date: 1 Sep 2004 03:37:42 -0700

As an attempt to shrink the size of radio, RF and microcontroller
board are separated with a flex PCB, instead of residing on the same
PCB. RF ground is connected to microcontroller ground through the flex
PCB. Besides ground, the are still a number of pins connected from RF
to microcontroller board. Both PCBs share the same 7.5V supply.

Separation of RF board and microcontroller board has caused a problem
which certain amount of distortion was measured from the transmitted
DTMF tone. A check on the radio without RF and microcontroller
separation showed that the distortion level was far lesser, 13% vs 5%.

The distortion disappeared when separate power supply was used for RF
and controller board. Can somebody shed some light on this?

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