International is the only company that I have found that will actually compensate the crystal in the oscillator. They do the same process that Motorola did when the element was initially assembled. There is more to it than getting the crystal to come on frequency. There are capacitors in the oscillator that offset the drift of the crystal vs. temperature. This has to be done in a temperature controlled environment where you can change the crystal temperature and plot the frequency vs. temperature graph. If this is the element that I think it is, the crystal is directly modulated. There are components that need to be changed to set the correct modulation index. This becomes a complicated procedure. I have the actual GE data for compensating one of their element. The document implies that a significant percentage of crystals were waste due to the inability of properly compensating them. Are you sure that Bomar cut the crystal for the proper channel element? There are at least two different elements for the VHF transmitter, possibly the same for UHF.
Not only is the capacitance important, but also, the temperature coefficient of the capacitors. Usually an International crystal is so close to the original Motorola crystal that there is no need to recompensate the element, except when the transmitter is exposed to extremes of temperature. 73 Glenn WB4UIV At 08:23 PM 12/03/03 +0000, you wrote: >I doubt that they are cutting the crystal any different whether they >install them in the element, or deliver them as-is. > >As far as compensation goes, what are they doing? Just changing the >cap parallel to the warp cap? If this is all they do, it is easy >enough to do myself, as it is only one cap, and the rules are the >same, more capacitance brings the freq down. > >The main problem at this point is the deviation issue. Are they >changing anything in the element to allow their crystal to meet >maximum deviation specs? > > > > > > >--- In [email protected], [EMAIL PROTECTED] wrote: > > You said, "Any insight is appreciated." This might be to late for >you, but > > help some others. > > 1. This is the very reason I stopped using the more "economical" >crystal > > companies. While their prices look attractive, there is usually >just to > > much rework, lost time, frustration, delays, and poor performance. > > 2. Send the ICOM / Channel Element in with your order and pay the >cost for > > xtal installation, testing, and compensation, I'm now 28 for 28, >worked > > right out of the box the first time, zero problems or failures >using this > > approach and dealing with ICM. Yes, it costs more, but its been >done right > > the first time, every time. > > > > Good Luck, > > Rob K7EI > > > > -----Original Message----- > > From: kk2ed [mailto:[EMAIL PROTECTED] > > Sent: Wednesday, December 03, 2003 11:06 AM > > To: [email protected] > > Subject: [Repeater-Builder] Micor UHF TX channel element/crystal >issue > > > > > > Hi all, > > > > I have a peculiar situation here - > > > > I just received two new crystals from Bomar (NJ) to refreq' two > > elements to 440 ham freqs. The channel elements are virgin >KXN1052's > > as prepared by Motorola. > > > > I installed the crystals, and after attempting to adjust the warp > > capacitors, both elements come up by about 12-15KHz on the high >side. > > I then went and placed aprox. 12-15pf caps in parallel with the >warp > > cap, which allowed me to trim the element on frequency, with a >swing > > of + or - 7 KHz or so, to allow for adjustments either way as the > > crystals age. > > > > Now the fun part - The original Moto factory 460 crytals yielded a > > maximum deviation setting of 8KHz or so, so there was no problem > > setting the IDC for clipping at 4.5 or 5KHz. HOWEVER, the new > > crystals will only achieve a Maximum Deviation of 3.75KHz or so, >even > > with the IDC control at max. I then pulled the caps I placed in > > parallel with the warp cap, and although the elements were 12KHz >high > > in operating freq, I was able to obtain a max deviation of 4.5KHZ, > > but still not 5KHz as desired. > > > > > > Question - is it possible that the crystals were cut with too much > > parallel capacitance to start with, then my adding the caps to get > > them to center freq just compounded the issue? > > > > Is the max freq deviation factor of the crystal proportional (or > > inversely proportional) to the crytal's internal capacitance? > > > > My calls to Bomar have been less than fruitful. I am still waiting >to > > speak to their "tech". They have offered to replace the crystals, >but > > I am afraid that the next set will be the same, as they seem to >think > > they are making them correctly. > > > > Any insight is appreciated. > > > > > > Eric > > KE2D > > > > > > > > > > > > > > Your use of Yahoo! Groups is subject to >http://docs.yahoo.com/info/terms/ > > > > > > >Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
