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Need help in designing high stability overtone crystal osil

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jinboqiu

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I use a 3 overtone crystal(fo=40.175MHz,CL=18pF,Req<35) to design an 160.7000MHz Local osillator(4x40.175MHz) in an
VHF reciever worked in 150MHz.I found it is very difficult to align the LO to 160.7000MHz.When I try to
change L16,L13 or C7,C74 to align the output signal to 160.7000MHz,the osillator often stop to work or
the output amplitude drop much(20-30db).
Can any one help me?
Thanks!
 

Borber

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Third overtone for 40.175MHz is 120.525MHz. 4th overtone (160.7MHz)!!!
is not possible
 

Encrypted

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You must make sure the oscillator is working at the third overtone. Remove the output filter and connect your analyzer to C67, tune C7 and check that the 40MHz output tunes smoothly with nothing below it. It may jump to ~13MHz at some point and now you are using the 12th harmonic and not the 4th as designed! Maybe this accounts for your losses?
 

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