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Clock-Block Clock Synthesizer

This product is no longer available.

The Clock-Block is a flexible frequency synthesizer that can be used for many timing and clocking purposes.

It accepts an external reference signal from 2 MHz to 50 MHz, and can be programmed via DIP switches to generate output frequencies in the range of about 500 kHz to 250 MHz. The output is a square wave at either 3.3 or 5 volts peak-to-peak. An on-board divider circuit allows the output frequency to be reduced by factors of 16 to 16384 for specialized applications.

One application for the Clock-Block is to replace the crystal oscillator of a PC motherboard to allow synchronizing the PC's clock to an external high-precision reference.

The Clock-Block is offered as an assembled and tested board. However, most applications will require some soldering to connect the board to the target hardware. TAPR does not have information about how to interface it to specific motherboards (though we hope to collect information from users about their installations and make it available).

The Clock-Block has selectable 5 volt and 3.3 volt regulators to allow easy interfacing to different logic levels. Typical current drain is less than 40 ma. The circuit board measures 2.0 by 2.6 inches.

NOTE: The Clock-Block is designed for timing applications, and not as an RF generator. Its phase noise is not suitable for use in radio applications.


The Clock-Block is available as an assembled and tested unit only. It uses a fine-pitch (0.65mm) IC that is difficult to solder without proper equipment.

Ordering Information

Sorry, Clock-Block is no longer available

Assembly and Operations Manual

The installation and operations manual can be found online at http://www.tapr.org/~n8ur/Clock-Block_Manual.pdf.


The TAPR Clock-Block was made possible by the efforts of:

John Ackermann, N8UR – Designer and Project Manager

Joe Borovetz, WA5VMS – Parts Liaison

Scott Cowling, WA2DFI – Manufacturing Liaison

Valuable design input was provided by:

Poul-Henning Kamp

Brooke Clark, N6GCE

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