[eagle] 70 cm Receiver Spur Source Found

Juan Rivera juan-rivera at sbcglobal.net
Sun Jun 10 12:42:28 PDT 2007


All,

 

The source of the spurs in the 70 cm prototype receiver is the CAN-Do
module.

 



This is the receiver IF output as designed

(powered from pins 39 and 40 of the CAN-Do Module)

 

 



This is the receiver running off of a separate power source

(bypassing the CAN-Do Module +13 volt output on pins 39 and 40)

 

 



This is the same configuration as above, but with the CAN-Do module shut
down

 

>From the above it appears that:

 

1.    The CAN-Do module is the source of all the spurs that I see

2.    None of the spurs are being generated by the receiver's internal power
supplies

3.    Some, but not all, of the noise is entering the receiver via the
switched +13 volt CAN-Do output on pins 39 and 40

4.    The remainder of the noise could be entering the receiver on other
CAN-Do pins, or being radiated to receiver components or traces in close
proximity

 

See my log for all the intermediate steps I took to reach these conclusions.

 

Remaining RF issues:

 

1.    Phase noise

2.    Microphonics

 

73,

 

Juan

WA6HTP

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