[VHFcontesting] Microwave modules repair

[MICHAEL SAPP]

Hi Folks: On the MMT tx, check all the tx transistors for proper bias voltage (.4 ~ .7 typical on base ), if  zero or 12~14 volts that device is likely toast (or no B+ getting to collector). I have seen the final output tuning cap that shunts to ground fail in a high vswr condition.  That puts the collector to ground and takes out the in-line fuse once the cap failure is a DC short condition. With the 404 and 432 MHz energy close to each other you can be led astray with a broadband RF power meter when attempting to detect low level signals. A high Q 432 Mhz filter can help as can a MMIC stage or two after the filter to the RF meter to get some sign of a 432Mhz signal coming through the system if no access to a spectrum analyzer is possible. (Likewise for the 404Mhz, sometimes those old gold twin cavity military filters are quite useful on the test bench).  Mike wa3tts