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Too much voltage is just as bad as not enough voltage
when feeding the 74AHC00 gate used to square
the buffered RF voltage up to a 3v square wave. Too much drive can cause the waveform to be non-
symmetrical (not 50% high and 50% low), while too little drive can raise the noise floor of the receiver
by introducing excess phase noise in the conversion process. We do not want to add any of the
following gain improvements unless they are needed.
Figure 124. Location of R63, PTO/VXO mixer gain adjust located in bottom left corner of board
If the voltage is too low, start by adding R63, (390 ohms – see above picture). See the LO mixer and
PTO section above for the parts placement. This change will provide a stronger VXO/PTO mixer output
to the input of the LO filter. Again, the TP3 measurement should be made across the band re-peaking the
LO filter caps C58 and C60 peaked for maximum voltage at TP3 mid band. If the voltage is now in the
1 to 1.5v range, we are done.
Norcal NC2030 v5
12-18-05
Page 99 of 128
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