HF Frequency Synthesizer Easier Than Ever

By Pierre Boillat, HB9AIS 20 Fin de Meyriez CH-3280 Meyriez, Switzerland

Translated from the January 1990 issue of old man

The first generation of HF equipment featuring digital frequency readout dedicated to Amateur Radio appeared on the market about 25 years ago. This technological development was much appreciated. Try to imagine, or remember, all the care that was needed when only analog displays were used, and when you wanted to make a sked on a specific frequency. It was certainly difficult to find the right frequency on your homemade receiver with a VFO and analog display.

Many improvements were made since that time. Chief among them was displaying the frequency of the VFO or the resultant mixing of the VFO, crystal and PLL. The results obtained are interesting, and therefore almost all modern HF transceivers are designed that way. Meanwhile, this is not easily achieved by the amateur. VFO design requires great care, both electrically and mechanically. The system becomes bulky and heavy. I looked for another solution—frequency synthesizers. I constructed a small transceiver for the 10-MHz band. Its frequency synthesizer was made from off-the-shelf components: 8 ICs (crystal oscillator and divider), some transistors, a Varicap diode, and about 40 other passive components. This was straightforward and worked well, but what I'm going to describe below is an even-easier method to build an HF synthesizer.

The Synthesizer.. .New Generation

A relative new LSI IC from Motorola® appeared on the market, the MC 145163, which is an HF synthesizer. This 28-pin IC may be directly connected to 4 BCD encoders for setting the desired frequency (see photo). The device contains a crystal oscillator; 2 programmable dividers, one for the reference frequency, the other for the VCO signal; a PLL LED output; and, two phase detectors.

Using this clever IC, we can build an HF frequency synthesizer with only one IC, saving 7 ICs and simplifying the wiring from my earlier design.

The Schematic

The HF synthesizer is composed of two basic parts: Parts a and b. An optional VXO is described in Part c. (See Fig 1.)

Part a—The Synthesizer

The synthesizer is based on the MC 145163, featuring a 4.096-MHz crystal oscillator whose frequency may be smoothly adjusted by means of a 5-65 pF capacitor. The crystal frequency is divided by a programmable divider, pins 5 and 6, by a factor of 4096, and thus the 1-kHz reference frequency is obtained from pin 25. The

Digital Frequency Synthesizers SchematicPll Frequency Synthesizer

Fig 1-4.5-9.999 MHz frequency synthesizer.

T1-3, 18, 2N2222 L2,471, Tore Philips No. 4322 020 97170, about 100 ¿¿H

T4, 8C2907 MC 145163, Motorola

L1,171, Tore Philips No. 4322 020 97170, about 15 /¿H BB 212, Philips

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