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September 1993 21

Directly sampling the SHF frequency can help keep synthesizer steps small.

Some tests were made between F1JSR and HB9AFO across Geneva Lake on a 30-km path, using both NBFM and FM ATV. The results were very interesting, particularly with the Gunn oscillator. The notorious drift of this kind of oscillator was so much reduced as to make an NBFM QSO possible! We didn't try SSB, though.

The prescaler has two outputs, which may come in handy in the SHF synthesizer application. The first output goes to the SP5052 synthesizer, the second to a frequency counter for control purposes.

Operation

As with most prescalers, without an input signal the IC may oscillate at about 650 MHz. The oscillation stops when a signal is fed to the input.

It might be useful to adjust the power-supply voltage between 4.5 and 5.5 volts to optimize operation. This is the only tweaking needed.

Don't worry if the 50-S2 output resistors and the IC become a bit hot; this is entirely normal.

And we saved the worst for last. The price for the whole unit is about 1700 French francs, or about $300. But that makes it still much cheaper than off-the-shelf professional 12-GHz counters. □□

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