ORDERING CRYSTALS FOR PHASE-LOCKED OSCILLATOR BRICKS N1BWT Jan 1994 There may be cheaper places, but all the crystals I've gotten from International Crystal (800-426-9825) have worked. For 10 GHz bricks, specify Catalog No. 585155 and the crystal frequency. This number is for a Frequency West MS-76, but should work for all the bricks made to the same Collins spec. For 6 GHz bricks, specify Catalog No. 585132 and the crystal frequency. This number is for a Frequency West MS-54, but should work for all the bricks made to the same Collins spec. You will also be asked if the crystal is ovenized - most of the ones with an internal oscillator are, but you should look. The oven is a little metal housing around the crystal with a transistor bolted to one side as the heater. There is also a cover over the crystal, either black rubber or aluminum. Current price is $18.45 each, with about one month delivery. Minimum order is $35, so pooling orders to buy at least two is a good idea. CRYSTAL FREQUENCY The 10 GHz bricks multiply the crystal by 108, so divide your desired LO frequency by 108. The 6 GHz bricks multiply the crystal by 60, so divide your desired LO frequency by 60. The 4 GHz bricks multiply the crystal by 39, so divide your desired LO frequency by 39. All of the bricks I've ever seen are above the respective ham bands, so I strongly recommend using high side LO injection. The frequency will tune backwards and the IF radio will need LSB to run USB on the microwave band, but your frequency calibration is never going to be exact anyway. The frequency after multiplication will be off by as much as 50 KHz, so plan for this when you select the frequency. I don't know if you can pull the crystal frequency anyway - I prefer to peak the oscillator and have it stable. Once the oven warms up, these oscillators are as stable as the average 2 meter transceiver. The bricks have an output interdigital filter. Most are tuned significantly above the ham band, so they will provide an LO for a 432 MHz IF but not a 144 MHz IF without retuning. Retuning is best done with a spectrum analyzer; if you are intent on doing it, check with me for suggestions. LO calculation example (ones I have used): 10368.1 + 432.2 = 10800.3, divide by 108 = 100.002778 MHz 10368.1 + 144.2 = 10512.3, divide by 108 = 97.336111 MHz 5760.1 + 432.2 = 6192.3, divide by 60 = 103.205 MHz 5760.1 + 144.3 = 5904.4, divide by 60 = 98.406667 MHz 3456.1 + 432.2 = 3888.3, divide by 39 = 99.700000 MHz Note that an IF of 144.2 MHz or 432.1 MHz puts you in danger of having IF feedthrough problems during a contest - a problem I've suffered with. My choices are limited by the limited tuning range of my IC202 and IC402. If you have a fancy multimode radio, you have a wider choice, but be careful. If you are going mountaintopping, repeater outputs start about 144.5, and packet stations around 145 MHz can provide constant noise - both can leak through and drive your IF radio crazy. (PS - bypass caps AND ferrite beads on your power, mike, and key leads will help with strong TV and FM stations on many mountaintops.) INSTALLING THE CRYSTAL The crystals are in a metal transistor can (TO-5). When you remove the old crystal, note that it has an insulator under the can with holes for the leads - save this and use it with the new one. New crystals have excessive lead length, which can short out inside (intermittently, of course). Cut the leads to the same length as the old crystal (around 1/4 inch) VERY carefully - if you shock the crystal, you might as well throw it away. Hold the lead with a pair of needlenose pliers between the can and the cutters to absorb the shock. Finally, hold the crystal with needlenose pliers and slip it into the socket - it may take a few tries to line up the pins, but don't force it and bend the pins (practice with the old crystal might help). Replace the spring clip, oven cover, and cover plate. TUNEUP Apply -19 or -20 volts as marked (the -20 volt units have an internal series diode for reverse voltage protection - not a bad idea). Connect a DC voltmeter from the "XTAL" terminal to ground and adjust the "REF ADJ" for maximum indication. Check the crystal frequency at the "REF MON" connector with a frequency counter - if it's an oddball connector, shove a piece of wire in to get a reading. Now connect an oscilloscope from the phase terminal (may be marked with Greek letter phi) to ground. There is probably a square wave present - that is the phase-lock circuit searching for the oscillator. Adjust the "CAVITY TUNE" adjustment gently (easy to break plastic shaft) until the square wave disappears and a DC voltage is present - the oscillator is now phase-locked. Adjust it back and forth to center the tuning in the lock range. If you have a frequency meter, check the output frequency to make sure it is locked to the right harmonic; if not, tune the cavity to a different lock point. Power output should be at least 10 milliwatts - if much less, the interdigital filter needs retuning. If mountaintopping in New England is contemplated, you might want to seal the brick in a ziplock bag, put it in the refrigerator for a few hours, then take it out and touch up the adjustments to be sure it will start cold. Some units have an "ALARM" terminal. This is a relay contact which closes if phase lock is lost; I've had it happen on cold mountaintops. Use it to light a warning LED.