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Do it yourself 100 khz crystal calibrator project kit
Note: This is a new revision of the board, which has some component changes. Be sure to review the newest documentation.
I have always enjoyed working with crystals and stable frequency sources. I put together a small WWV spotter in helping to debug and repair the radio receivers I work with. I found that I wanted to formalize the process, so I designed this small circuit board. It contains a Pierce crystal oscillator, with a Hartley modulation oscillator and can be loaded with parts for MHz crystals, or 100 kHz crystals.
When configured with the 100 kHz crystal, as supplied with this kit, it operates like one of the Heathkit, Drake, Hammarlund, or similar crystal calibrator, putting out frequency markers at 100kHz intervals well past 30MHz. These are really nice with older analog radio, which need markers to help on calibration. If you want to use MHz crystals, you will have to provide your own parts and figure the final values to optimize the performance.
Because of the high-speed edges on the CMOS IC used in this project, you will get harmonics at 100kHz intervals well beyond the performance of some of the older crystal calibrators (past 30MHz). I have tested it with my Redsun RP2100, Sony ICF-SW7600GR, as well as my BC-342 and BC-312 shortwave radio receivers over their whole frequency ranges. The crystal supplied is specified at +/-30ppm (0.003%) by the supplier, and a tweak capacitor allows tighter adjustment. That translates to +/-300Hz at the 10MHz harmonic of the output. Which will work nicely for most radios except for the tightest SSB and CW filters. The modulation oscillators allows it to be used with standard AM receivers which do not have a BFO.
It is set up to take two AAA (LR03) batteries on the rear, so it is truly portable. The current drain is approximately 2mA, increasing to 4mA with the modulator on. An alkaline AAA battery is rated for about 1500mA-hours, so if you only turn it on when you need it, the batteries will last almost their shelf life.
You can see the parts list at http:// /Fun/Crystals/cal_man.pdf. You can see more at "grandadselectronics.html" in the root directory of the novatech-instr.com page. You can get all of the parts at Mouser and Digi-Key, if you wish to build your own from the schematic.
This is the complete kit of parts. The second photo shows the kit of parts. I put up a photo of an assembled unit sitting with a Heathkit HD-20 Crystal Calibrator, to give you a sense of the size. Note that this kit does not include a case: it is for the printed circuit board and the electronic parts only.
I added another page to the PDF, which shows a modification that can be made to allow this board to be mounted on an octal base and derive power from an old tube radio receivers. You leave off the batteries, drop the B+ from the receiver through a resistor, and regulate it with a zener. These parts are not supplied with the kit. Other modifications are possible as you see fit.
I mentioned it on the schematic, but I want to point out that the crystals used on this project might not be "pullable" enough to get an exact zero beat. That is a property of the small cylinder crystals. Your final error could be on the order of +/-3 Hz at the 100kHz fundamental. Depending upon the exact tolerances on your kit, you should be able to get exact zero beat. I have a promise of 100% satisfaction, so if you can't use one of these that you built, I will refund the full amount, including your postage to return the item (domestic only). We are now pre-testing every crystal for pulling range before including them in your kit. (we have found that even with this, some crystals are out of spec, so we are including two with each kit)
You need basic electronic tools (pliers, wire cutters, soldering iron, etc.), know how to read component codes and understand schematics to build this kit.
(Grandad's Electronics is a registered trade name of Novatech Instruments, Inc.)
