Browsing one of the regional electronic (online) shops, I found a 2030kHz crystal, which would be perfect for a couple of projects. The order seems a little odd, however, the order reflects the difficulty of the different projects, the further down, the more difficult to realize.
For the typical SDR, one could simply feed this signal into two Flip Flops, resulting in an SDR LO of 507.5kHz.
With a minimum sampling rate of 24kbps, a range from 495.5kHz to 519.5kHz would be covered. This is in particular interesting since 518kHz, the international NAVTEX frequency falls into this range.
Taking one of the two 507.5kHz signal and feed it into two further Flip Flops would provide an SDR-LO of 126.875kHz, which would provide a frequency range of 114.875kHz to 138.875kHz, covering the 136kHz amateur radio band.
40m QRP Superhet
As non SDR use of the crystal, a more classical approach is in reach: a 2030kHz (super-)VXO and a 5000kHz crystal filter coincides nicely with the 40m QRP frequency. The 2030kHz crystal could additionally penned down (see earlier post about xtal-penning) to cover lower frequencies in the 40m CW section.
20m QRP Superhet
Also the 20m QRP frequency is easily covered. The trick here, a 2030kHz (super-)VXO as LO for a subharmonic mixer, which per se doubles the LO-frequency. Hence, the effective LO-frequency would be 4060kHz. In such a concept, it would be somewhat obvious to use a 10MHz crystal filter.
10m QRP Superhet
Similar to the 20m concept, a subharmonic mixer would be required. As intermediate frequency, 24.000MHz would be obvious. However, watch out for the correct crystals for the filter! Most crystal will be overtone crystals, for a cheap filter we would need fundamental frequency crystals, and yes, they do exist for 24.000MHz.
40m LSB Superhet
Here is a simple one. The sum of 2030kHz and 5068.8kHz results in 7098.8kHz. I would propose to build a full-lattice filter with two original and two penned down 2030kHz crystals. As LO a super-VXO using 5068.8kHz crystals would an obvious choice. Additional options would be a 5120kHz VXO (getting us to 7150kHz), a 9216kHz VXO (9216-2030=7186), or, for some of us, a 5200kHz VXO (7230kHz).
80m LSB Superhet
This could be a tricky one. I would, once again, propose to build a full-lattice filter with two original and two penned down 2030kHz crystals. A conceivable could employ a 5.74MHz ceramic resonator. Subtractive mixing would provide a range, depending how far one pulls the VFO, of a couple of 10kHz about 3710kHz.
There may be more uses of this crystal, feel free to add comments with additional ideas!