Nate Duehr wrote:
On 2/2/07, Kevin Custer <[EMAIL PROTECTED]> wrote:
The article isn't intended to educate about the use of GE MASTR II
ICOM's in specific, or what stability one would achieve when the crystal
is correctly compensated. For that information, one would go to these
Ok Kevin, you got me there. I went to GE because GE is what I know. So...
Maybe the better question is:
Which manufacturers ever created crystal modules that were less than 2
PPM in UHF service in "normal" temperature conditions?
I don't know that any commercial manufacturer did, but that's not the
point. The point is if someone stuffs a new crystal in a 5C element, it
MAY NOT hold to its OEM specifications no matter the temperature
change. Are you going to guarantee that any recrystaled 5C is going to
be 2PPM in the 'normal range' if the recrystaled ICOM was not
temperature compensated? I didn't think so.
The whole point of the article is to get people to send their elements
to a reputable crystal manufacturer to have them
temperature-compensated, rather than just replacing the crystal and
crying when it doesn't work right or even begin hold frequency. ICOM's
still have a temp-comp capacitor in the oscillator circuit that must be
selected to match the crystal just to get the unit to be within its
rated stability over the 0-55C temperature range. Outside that range,
the ICOM temp-comp circuit kicks in and provides additional warping of
the crystal to help maintain its stability.
Motorola channel elements have a much less sophisticated temp-comp
circuit (compared to the GE ICOM's) that relies on some thermistors and
capacitors that must be chosen carefully and tested over temperature.
The Motorola elements are not sensitive to changes in supply voltage and
don't have the 0-55C stability band that ICOM's do. Each element has its
own internal temp-comp components, unlike the EC ICOM's which depend on
help from an external temp-comp circuit in a nearby 5C ICOM.
There are other "elements" besides 5C, 2C, 1C and EC ICOM's, and my
article deals with all aspects of frequency determining assemblies.
If no manufacturer did it, why the warning?
SHOW ME in the text where it says "WARNING", or "You HAVE TO use a 2C
on UHF. 2C is a common option on a UHF repeater. I never said it was
mandatory to use 2C or better elements; I just stated the reason why
someone might want to use them on the higher frequencies, period.
Read what it says, and don't read any more into it.
Kevin Custer
