26 Oct 2010

Stable, simple, stand-alone, 8.970kHz source?

What do people think is the simplest way of generating a stable 8.970kHz (kilohertz) frequency that does not require a PC when running? I thought of an HF crystal divided down by 256, but have you tried to buy a "made to order" crystal lately? I need this for my VLF tests this coming winter.


Jan, PA9QV said...

Idea : use a 27.555MHz 3rd overtone Xtal (oscillating on 9MHz) and divide by 1024 should provide you with 8969.7Hz

Close enough?

A bit further away : 27.000MHz 3rd overtone (more common) should provide 8789.1Hz

73 de Jan PA9QV

Roger G3XBM said...

Thanks Jan. Rik OR7T has also suggested this approach which looks a simple low cost way of doing the job.

LY2SS said...

atmega/attiny (arduino) clocked from xtal, with some custom code? One can even get sinusoidal signal if needed.

Anonymous said...

Hi, This is David - WB4ONA...

I Agree with LY2SS. Use a crystal clocked AVR running DDS sine wave firmware.

Below is a link to a project that does this. The code is simple once you understand the basics of how a DDS works (download app notes for Analog Devices).

Don't use a PIC uC; use an AVR. Typically most PICs use four clock cycles per instruction. The RISC AVR's typically use 1 clock per instruction. A four-times improvement in speed for this application (I continue to scratch my head when I see sooo many people using lame PIC processors).

An AVR clocked at 20MIPS will make a nice DDS that can work through 100kHz with sub-sub-Hertz tuning, that's with an 8-bit R2R A/D. Optimally, you should program this DDS stuff in assembler and optimize the number of clock cycles used.


Best 73's...