Sunday, October 24, 2010

2048kHz XTAL

Haven't got the luck to obtain any of the before mentioned 2030kHz crystals? Well, there is hope ;-)
What about the 2048kHz standard crystal? This one should be widely available.
Let's see what we can do with this one. First of all, such crystals can be penned down, 18kHz should be doable. But what more can we do?

600m I/Q-SDR
For the typical SDR, one could simply feed this signal into two Flip Flops, resulting in an SDR LO of 512kHz. With a minimum sampling rate of 24kbps, a range from 500kHz to 524kHz would be covered. This is in particular interesting since 518kHz, the international NAVTEX frequency falls into this range.

2200m I/Q-SDR
Taking one of the two 512kHz signal and feed it into two further Flip Flops would provide an SDR-LO of 128kHz, which would provide a frequency range of 116kHz to 140kHz, covering the 136kHz amateur radio band.

40m Digi-Mode Superhet
As non SDR use of the crystal, a more classical approach is in reach: a 2048kHz (super-)VXO and a 5000kHz crystal filter coincides nicely with the 40m digital mode range. The 2048kHz crystal could additionally penned down (see earlier post about xtal-penning) to cover the 40m WSPR and PSK frequencies.

20m Digi-Mode Superhet
In the 20m band, the WSPR frequency is easily covered. The trick here, a 2048kHz (super-)VXO as LO for a subharmonic mixer, which per se doubles the LO-frequency. Hence, the effective LO-frequency would be 4096kHz. In such a concept, it would be somewhat obvious to use a 10MHz crystal filter.

10m CW 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 2048kHz and 5068.8kHz results in 7116.8kHz. 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 7168kHz), a 9216kHz VXO (9216-2048=7168), or, for some of us, a 5200kHz VXO (7248kHz).

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 3692kHz.

4096er Grabber Receiver
You may remember that my 30m grabber receiver employs a subharmonic mixer. Well, the exact same can be done for the 4096er hf-beacons. However, those beacons spread a little bit more than the 100Hz wide 30m QRSS segment, therefore, I would skip the crystal filter. This would have the advantage of also showing beacons below the 4.096MHz nominal frequency in a good old fashion DSB way.

4096er I/Q-SDR Grabber Receiver
One of the most popular entries on this blog is concerned a subharmonic I/Q-SDR in which the 90 degree I/Q phase-shift is done on half the frequency and hence amounts to 45 degrees on the subharmonic local oscillator. The exact same could be done for the 4096er beacon range (click here for more info) using a 2.048MHz crystal and some RC/RR network as shown in the subharmonic SDR article.

There may be more uses of this crystal, feel free to add comments with additional ideas!