> Hmmm Seems I am batting 1000 on crystals for my Micor > Transmitter from JAN. First crystal was low in Freq. and Now > the Second is as well. I am not sure if there could be a > reason other then they are cut wrong as I have done the > following to check different things
The first time I used JAN was probably twenty years or so ago. It was also
the last time I used them.
But anyway, on to your problem.
With Micors, when you recrystal a channel element, more often than not you
have to change the value of a fixed capacitor in the element to center it
within the warp range of the trimmer. If your new frequency is lower than
the original element frequency, usually you will have to increase the value
of the capacitor, and vice-versa. That capacitor will also affect the
temperature compensation. If the repeater will be in a temperature-stable
environment, usually you can get by putting an NP0 cap in there, but not
always. Sometimes the factory cap will not be NP0, i.e. it not only its
value but also its temp coeff was selected to obtain the required
temperature stability.
I have a few parts bin drawers filled with NP0 ceramics in the range of 15
pF to 47 pF that I delve into when re-crystalling Micor elements. I usually
recrystal elements myself if they are going to end up in a controlled
environment, but at sites where I have equipment in outdoor cabinets or in
elevator penthouses that vary widely in temperature, I send them to ICM.
I don't have a Micor element where I'm working today, but off the top of my
head, if you take the cover off the element and look behind the trimmer, you
will see a fixed cap (probably somewhere in the 15 to 39 pF range) at a
little bit of a slant. If I'm remembering it right, one of the cap leads
connects to a trace that runs along the edge of the board, and the other leg
connects to a pad that also connects to the trimmer. Maybe someone has one
handy and can give a better or more accurate description so you can find it.
What is your frequency, the original channel element frequency, and how far
off is it with the trimmer more or less centered?
--- Jeff
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/Repeater-Builder/
<*> To unsubscribe from this group, send an email to:
[EMAIL PROTECTED]
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/
<<attachment: winmail.dat>>
