You still need a stable reference oscillator somewhere. You only cancel
the drift of the first L.O. If the reference oscillator drifts by a
ppm, your overall frequency calibration drifts by a ppm.
73 Martin AA6E
wa3fiy@radioadv.com wrote:
What about the Wadley Loop? It is my understanding that it provided a
high degree of stability using a tunable (read drifty) VHF oscillator and a 1
Mhz crystal oscillator rich in harmonics along with a unique mixing scheme.
Several commercial receiver designs took advantage of the Wadley Loop
design including the Yaesu FRG-7, Drake SSR-1 and some RACAL
receivers.
Here is what Wikipedia has to say:
"Of the three principal methods of such control, the Wadley Loop seeks to
cancel any tendency for the oscillator's frequency to drift. It does this by
mixing the received frequency up to a high IF frequency (more than 10
MHz) and then uses the same oscillator to generate a lower frequency.
These signals are then remixed to generate the second IF frequency."
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