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. 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! 73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of dgrapach Sent: Wednesday, July 11, 2007 5:46 PM To: [email protected] Subject: [Repeater-Builder] Re: crystal/channel element compensation.. --- In [email protected] <mailto:Repeater-Builder%40yahoogroups.com> , [EMAIL PROTECTED] wrote: > > At 7/10/2007 20:42, you wrote: > >Bravo to you for doing the right thing! Far too many people these days are > >in a rush to get a repeater on the air right away, and figure that it's okay > >to bypass the compensation steps. I guess they have the money to go back > >and fix the problem they created, later and at considerably greater cost. I > >went to the "do it right the first time" school. > > My experience with ICM has been rather negative, so considering how much > they charge I stay away. I've been using West Crystal for a few years now > & am quite happy with the results; I only wish the exchange rate wasn't so > unfavorable. > > & I don't bother with compensation; I temperature stabilize. For me, it's > the "right thing". > > Bob NO6B > > P.S.: Anyone know of a source for retrofit DDS modules for G.E. MVPs? The > DDS chips are getting cheap enough now that a finished product for older > LMR equipment should be economically viable. > Hi Bob What is the difference between temp compensation and temp stabilize. I take it the temp stabilize is a heater. If so what temp would you limit it at and why is it better if it is , and how would you do it. Denny
