CCWN76:95



I have taken considerable oains in this circuit to insure that
logic noise at harmonics of 1 I'liz do not leak out of the enclosure
through the power supply connection. This is extremely important,
because when you are operating with a 9 MHz i.f., any small
leakage will produce a coherent birdie right on the spot you
want to hear your signal.
The circuit of Fig. 2 works very 3imilar to that of rig. 1. The
crystal oscillator is set to approximately 50 KHz above a harmonic
of 500 KHz- I've made it 500 kHz instead of 1 MHz so that the
circuit can be used on 80 Meters. Instead of the D flipflop
mixer of Fig. 1) I use a sampling circuit. 'Arnen the offset frequency
(in this case 50 kHz) is more than a few percent of the sampling
frequency (in this case 500 KHz) the flipflop circuit generates
quantization noise which badly degrades the spectral purity of the
system. The 74LS02 generates positive 10-nanosecond pulses which
strobe the sampler) Q4. 7he current output at the drain is a
chain of Dulses at 500 Khz which increase and decuease in intensity
at the offset frequency, approximately 50 KHz. The 50 kHz tank
then smoothes these current pulses into a 50-kHz sinewave voltagej
and the CD4000 gates amplify it to a nice 12-volt pk-pk sqilaeewave.
IC4 locks the crystal oscillator in precisely the same nanner as
I described for the circuit df figure 1.