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Rob,
This topic has been covered repeatedly on the repeater-builder
list, but apparently not so often on this list, so I'll summarize the
postings.
It is definitely necessary to send the channel element in for
re-crystaling. When you order a bare crystal, intending to install it in a
channel element that has been previously compensated, it will *not* maintain 5
ppm. That's because the bare crystal is manufactured to the nominal values
of the channel element as stated by the radio manufacturer, and your
previously-compensated channel element has components that may be far from the
nominal values. This fact has been proved many times by many people,
including me. One of my fellow hams, who maintained that you could "just
order the crystal and change it yourself" found out the hard way: The
crystal he received was made for nominal channel element values, and when he
installed it in a previously-compensated channel element, it only barely could
be set on channel and it drifted off frequency quickly when the ambient
temperature changed. He then sent the crystal and the channel element back
to ICM for proper compensation, and once it was put back in service, it was
rock-stable. Duh!
Another reason for sending the channel element in for the crystal house
to rework is that the modulation sensitivity can be verified right on the
production line. I don't know if the cheaper houses make this important
test, but I know that ICM does, and that's one reason why ICM gets my
business.
73, Eric Lemmon WB6FLY From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of RK Barba Sent: Friday, April 14, 2006 1:09 PM To: [EMAIL PROTECTED] Subject: [GE Mastr II] Changing Icoms I have been following these messages. I have
serviced a number of UHF Mastr II repeaters that are multi freq. and had (1) 5C
RX icom and all TX and the other RX elements were EC. These repeaters were
supplied new from GE at the time for a regional MED radio system buildout. The
shop manual states 1 5C will provide compensation for all EC elements in the
radio. 2C will not provide external compensation. There is no need to send
elements back to ICM or Bomar. Just order the xtal and change it yourself. 5C
= 5ppm ,without compensation all elements will provide 2ppm at 32*F to 131*F
temperature range.
Rob
YAHOO! GROUPS LINKS
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- [Repeater-Builder] RE: [GE Mastr II] Changing Icoms Eric Lemmon
