View Single Post
Old 3rd May 2019, 2:44 am   #12
John KC0G
Hexode
 
Join Date: Mar 2009
Location: Minneapolis, Minnesota, USA.
Posts: 275
Default Re: Arduino based DDS with 898 Eddystone dial

To see how the 898 dial works, see the article by Gerry O'Hara on the HBR-13 receiver at: http://eddystoneusergroup.org.uk/Tec...20Receiver.pdf

The logging wheel has 100 divisions. There are markings of 0, 100, ..500 on the dial, and so there are 500 divisions. The spec states that the 898 has a 110:1 reduction ratio. I have just tried an unused 898 and it took ca. 55.75 turns of the knob to go through 500 divisions.

Thinking out loud, if the 898 covered a bandspread of 250kHz, you would have a tuning rate of ca. 4.54 kHz per turn of the tuning knob. If you wanted a tuning increment of say 10Hz, a 128 ppr encoder with quadrature detection (giving 512 ppr) might work. You would need to provide a scaling factor in the Arduino. The encoder would not be cheap. And you would have to set the Arduino to the dial, eg by setting the dial to mid-point on power-up, and pressing a sync button.

Good luck and 73

John
John KC0G is offline