To the best of my knowledge, the crystal is always manufactured first to meet ICM's nominal specifications, and the channel element is then modified as necessary to perform satisfactorily with that crystal.
73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of kk2ed Sent: Thursday, March 29, 2007 9:04 PM To: [email protected] Subject: [Repeater-Builder] Re: ICM Crystals Off Frequency? Ok, but back to my original question - when ICM does an element - do they cut the crystal first to "their standards", then modify the element to make it work? Or are they measuring the element first in some fashion, then cutting the crystal to the "known" element characteristics? --- In [email protected] <mailto:Repeater-Builder%40yahoogroups.com> , "Eric Lemmon" <[EMAIL PROTECTED]> wrote: > > Each channel element, regardless of the manufacturer, contains a number of > resistors, capacitors, and perhaps a few inductors. The capacitors have > specific TCs (Temperature Coefficients) that are chosen so that the > capacitance variation with temperature change is exactly complementary to > the reaction of the crystal. When performed correctly, the capacitors > change value with temperature just enough to cancel out the frequency drift > of the crystal. > > However, a full compensation of the crystal holder (channel element, ICOM, > etc.) includes more than temperature compensation. The technician also > verifies that the crystal can be set exactly on frequency with the included > trimmer, that the output amplitude meets the minimum specification, and that > the crystal is "rubbery" enough to be modulated to the required deviation > level. > > As you might expect, full compensation of a channel element to a particular > crystal is an exacting and time-consuming process. That's why ICM charges > more for the compensation than the crystal costs. > > When a radio user orders just the crystal and puts it into a handy channel > element, the components inside that channel element may or may not match the > characteristics of the new crystal. As you and many others have discovered, > the new crystal may be such a poor match to the channel element that it may be > impossible to get it to operate on frequency. Even if you can add or remove > some shunt capacitance to tweak the crystal onto frequency, that shunt > capacitance is not temperature compensated. It may work fine, and it may > not. > > Both Motorola and General Electric operated their own crystal manufacturing > facilities for many years. Since each company had complete control over the > making of both the crystal and the channel element that contained it, they > could evolve the processes to optimize performance and longevity. Let's say > that Motorola found that their MICOR channel elements worked best with > crystals that were made for a 25 pF load rather than a 30 pF load. If you > have one of these original MICOR channel elements that you want to > re-crystal, it is likely that ICM or Bomar or Crystek will ship you a > nominal crystal, since they have no way of knowing that your channel element > is not nominal but has already been compensated to the original crystal, > which may have a non-nominal load capacitance. How can they know, if you > don't send in the channel element? Also, since the crystal house never had > the chance to test your channel element first, they have no obligation to > make changes to your crystal if it doesn't work properly once you install > it. > > Given that a full compensation is a one-time charge, I personally have every > crystal I buy given the full compensation in a channel element I send to the > crystal house. I think it's a prudent investment. Not everyone agrees... > > 73, Eric Lemmon WB6FLY > > > -----Original Message----- > From: [email protected] <mailto:Repeater-Builder%40yahoogroups.com> > [mailto:[email protected] <mailto:Repeater-Builder%40yahoogroups.com> ] On Behalf Of kk2ed > Sent: Thursday, March 29, 2007 7:49 PM > To: [email protected] <mailto:Repeater-Builder%40yahoogroups.com> > Subject: [Norton AntiSpam] [Repeater-Builder] Re: ICM Crystals Off > Frequency? > > > Here's a question I haven't seen answered, but I'm sure a few of us > would like to see answered - > > What exactly is ICM and others doing when they "compensate" or match > an element with a crystal to get it netted on freq? > > I've had mixed success. Some crystals & elements tune on freq just > fine, while some don't. I've had mixed luck padding extra > capacitance on Micor elements, but Mitrek elements use the inductor > instead. > > For example, I have a KXN1052 with a crystal that is 20KHz high after > dropping it in. I can pad the trimmer, but then the element won't > produce more than 3KHz deviation max. > > > What's their secret? The only thing in the element is resistors and > capacitors! I'm sure those of us capable of working on a repeater are > capable of changing a few components. > > Anyone??? >
