There IS an article about temperature compensating channel elements on r-b. Go to the Technical Information section and search for "Why should you really spend $50 to re-crystal a channel element or ICOM?"
While the method you describe will get the crystal to operate on-frequency at room temperature, it won't deal with temperature compensation or aging, which could be vital depending on the location of the equipment. Many repeaters are at commercial sites and having your equipment put out clean, on-frequency, properly deviated signals, is the responsible thing to do. If the site is only accessible part of the year, you don't want to be constantly going up there to re-net the channel elements. Bob M. ====== --- kk2ed <[EMAIL PROTECTED]> wrote: > I posted on this subject awhile back. Do a search on > posts by my > user name. > > Basically, there are two caps towards the edge of > the circuit board > (opposite of the trimmer/socket end) that vary > anywhere from 5- > 33pf. Install the crystal, then play with the value > of these two > caps. I have found that I usally need to reduce the > capacitance a > little, and the crystals net right on. I've never > had to change an > inductor. > > Pick up the small capacitor assortment that Radio > Shack sells - it > has about 50 caps in the 5-33pf range. I use them > all the time to > replace the original caps in the elements. > > Before you start changing the caps, first install > the crystal and > fire it up, and while watching your frequency > counter or service > monitor, set the warp trimmer to midpoint (halfway > between the > lowest and highest freq settings possible). Then > start playing with > the capacitor value until the crystal is as close to > your desired > frequency as possible. This simple step will ensure > that you can > adjust the crystal adequately up or down as needed > in the future, as > well as the initial setup. If the capacitor swap > gets you within > 2Khz or so, the trimmer should have enough "pull" to > net you on > center frequency. > > If I recall, the capacitor in question is usually > red, and while > holding the element component-side up and plug-in > end towards you, > the cap is to the far left corner. > > Speaking of elements, I need to call Bomar tomorrow > - a one-year old > 440MHz repeater crystal decided over the weekend to > jump 25Khz high - > right onto the input of another repeater! Same PL > no less! (Here in > the NE every other 25KHz pair flips low-in hi-out > and vice versa) > > I think someone was going to take my original post > about > compensating elements and place it on > repeater-builder, but I never > noticed it there. Hopefully it will save others > some money. It > always amazed me that guys would embark on a large > project building, > wiring, and tuning a repeater, but the simple task > of re-crystalling > and netting elements always seemed to be > intimidating. Most likely > due to lack of info being published on the subject. > > > Eric > KE2D > > > > > > --- In [email protected], "w4dg.geo" > <[EMAIL PROTECTED]> wrote: > > > > > > I recently ordered TX and RX crystals from ICM for > the MICOR RT > Station. > > I specified the correct FC and FX and catalog # > 167380 for MOT > KNX1018C > > TX (132-174). When these crystals were received > they would > not "net" on > > frequency. The TX was over 20Khz. high and would > not net any > closer. I > > notified ICM and their Customer Service Dept., > agreed to replace > the TX > > crystal. When I received this "replacement > "crystal, it was over > 30Khz. > > high! I sent another email and got a reply from > the owner, Royden > > Freeland, W5EMH, stating the following: > > > > "To get the crystal to tune properly you will need > to change L1 to > > 2.6-2.7uh and C6 to 1-10 pf depending on the > crystal to get it on > > frequency at close to center trim. Each element > was compensated and > > tuned for the original crystal so if you are > changing frequency > very far > > there can be problems. Motorola generally used a > crystal load of > 32pf > > in elements with trimmers and varied components > within the element > to > > bring it on frequency. ICM will be happy to > install the crystal and > > compensate the element if you would prefer. We > would charge > $60.00 to > > install and compensate your element and crystal". > > > > I have printed out the channel element schmetic > and picture (from > W3KCC) > > repeater-Builders website and see that C6 is the > trimmer and L1, > but no > > values are represented. Can anyone tell me what > the current value > of > > the inductor L1 is? If it's currently higher in > value, can it be > > "rewound" for the 2.7uH inductance ICM references? > I believe > there is > > enough room to insert a fixed cap of proper C in > series to drop the > > tuning range of the C6, to perhaps the 1-10pf. I > have looked at > Mouser > > Electronics for a trimmer 1- 10pf and 2.7uH > axil-lead inductor, > > L1without success. > > > > If they are available, can you please stear me to > where I can > purchase > > one or both? > > > > I always thought that you sent ICOM's back for > temperature > compensation > > and not for simple exchance of crystals. I have > never needed to > to that > > with any GE MASTR series TX & RX or Mocom 70 > series or any EF > Johnson > > series that simply required new crystals. But > again, that was 20 > years > > ago, which is a long time. > > > > Any advice would be appreciated as I don't need to > spend another > $120 to > > "install the crystal and compensate the element". > > > > TNX is advance...Dennis - W4DG ____________________________________________________________________________________ Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now. http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ
