Ok, thanks for the responses, Eric. That's what I would suspect. I have had past issues with Bomar where their crystals were ALWAYS 10KHz or so high, and always needed extra trim capacitance to net them. Two orders or so back, I spoke to their engineer, who made a mod to their specs to lower the loading capacitance. The replacement crystals netted with no additional capacitance, and deviation range was fine. Worked perfectly in a number of different KXN1052 elements at the time. It seems that even though I requested my most recent order to be made to this modified "spec", they failed to do so. Now off to call them and get it resolved.
Eric KE2D --- In [email protected], "Eric Lemmon" <[EMAIL PROTECTED]> wrote: > > 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" <wb6fly@> > 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??? > > >
