The XOR Subtractive Mixer is ideal for higher frequencies too. I built this 500KHz version for QRP on the 501KHz to 504KHz Band.
A 13.5MHz Crystal Oscillator is configured as a VXO this is subtracted from a 14.0MHz Modulated Crystal Oscillator to produce 500KHz. This goes via an LPF to an Inverter PA, on the underside of the board, which produces 150mW of RF via a further LPF.
The Output signal is very Pure and Stable. Frequency stability can be seen from the following decodes in a 5 hour period.
091113 1050 13 -17 -0.1 0.503923 G3ZJO IO92 17 0 1 0
091113 1250 14 -18 0.8 0.503923 G3ZJO IO92 17 0 1 0
091113 1520 14 -18 1.8 0.503923 G3ZJO IO92 17 0 1 0
