At 06:17 PM 07/11/07, you wrote: >I thought this horse was beat to death several times before, but he (she?) >seems to cling to life! > >Although "temperature stabilization" has a desirable ring to it, it is not >the answer. Having a transmitter building that is maintained at a constant >60 degrees (for example) is irrelevant; the crystal buried deep inside the >radio is running much hotter, depending upon the operation of the >transmitter. The temperature stabilization of the room containing the radio >cannot be relied upon to stabilize the frequency of the crystal- that's the >job of temperature compensation. > >However, as has been pointed out by many people in the past few months, >temperature compensation of the crystal is only one of several >"compensation" functions performed by a professional crystal supplier. >There are at least four objectives: >1. Temperature-compensate the crystal so that its frequency changes due to >temperature are negated; and >2. Ensure that the crystal can be adjusted exactly on center frequency with >the trimmer; and >3. Ensure that amplitude of the channel element's output exceeds the >minimum specified value; and >4. Ensure that the crystal is "rubbery" enough to be fully deviated within >specified limits.
5. Ensure that the deviation is symmetrical above and below the center frequency. I've got a couple of crystals here that were built by a local driftal house that have twice the positive deviation than the negative deviation. >Inasmuch as very few of my esteemed colleagues have the necessary laboratory >equipment, expertise, training, time, and money to perform all of the above >tasks in a manner that meets the manufacturer's specifications, I must >assume that any self-performed "compensation" falls far short of the mark. >I personally do not have the equipment, time, or desire to undertake the >precise and exacting task of performing a complete compensation of a channel >element- but even if I did, I could not justify my time and effort when the >crystal houses can do it better and for less cost! It's a no-brainer: $30 >for a complete compensation is a bargain. There's a lot more to it than >simply changing a few capacitors! So true. NO6B uses a thermal conductive glue to mount a resistor to the side of the crystal. A temperature sensor is used to measure the instantaneous temperature and adjust the DC current through the resistor to keep it steady. See <http://www.repeater-builder.com/construction-proj/no6b-crystal-heater.html> Mike WA6ILQ
