Tuesday, January 12, 2010

500kHz - using old CB crystals

Some more brainstorming with Jan resulted in the emerge of the idea to use CB crystals for generating a stable signal on 600m.

In an earlier post, I disclosed the use of CB crystals for the 136kHz band. To that time, I mentioned that the same game could be done for the 500kHz band too.
Now that I actually are allowed to transmit on 501 to 504kHz, it is time look into this as well.

In order to get to the 500kHz band, one needs to the divide the 27MHz frequency by 54.
Since CB crystals usually are overtone crystals, we could simply let them oscillate on their fundamental frequency, that would leave us at 9Mhz (gate oscillator / VXO / superVXO). A decade counter (74HC4017) easily divides by 9, which will result in a 1MHz pulse. This pulse is put to a flip-flop generating a nice, symmetric 500kHz signal.

CB (R/C) frequencies that could possibly used in the indicated range:
  • 27.055 / 54 = 0.501018
  • 27.065 / 54 = 0.501204
  • 27.075 / 54 = 0.501389
  • ....
  • 27.205 / 54 = 0.503796
  • 27.215 / 54 = 0.503981
 Let's go soldering!

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