500kHz as simple as it gets

We want to reach 501kHz to 504kHz. Here are some easy options, I not sure which one I will go for, depends on the crystals I got in my box.

1. Subtract 2.000MHz from 2.500MHz => 500kHz obviously.
   This will obviously work with any pair of crystal having a 0.5MHz difference.
   
2. Subtract 4.000MHz from 5.000MHz => 1MHz divide by two =>500kHz
   This will obviously work with any pair of crystal having a 1MHz difference.
3. Subtract 8.000MHz from 10.000MHz => 2MHz divide by four  =>500kHz
   This will obviously work with any pair of crystal having a 2MHz difference.

I agree, one could go further, but, with bigger differences, drift will cancel out less efficiently. The more one divides, the more both oscillators have to be pulled in order to cover the band.


A design could involve the following:

• Modulated Pierce oscillator for the upper frequency. This oscillator will generate a frequency above the crystals series frequency.
• Moderately pulled (downwards) VXO for the lower frequency. This oscillator is will set the operating frequency.
• Dividers, if required, could be FlipFlops.
  

Now, what's in my box of crystals??