One other possibility is that the I.F. stages are aligned
improperly which to a trained ear ( distortion/flat-topping of part of the
sine wave to what you are hearing) could be mistaken for "off frequency" .
If the IF alignment was performed at some time with the channel element not
set properly, in theory it is very possible to mis-align the I.F. my accident.
The proper procedure is to set the L.O. injection first using a
service monitor to "sniff" the L.O. and then check and align the I.F. as
needed. Keep in mind, most of the Mastr II's we see these days have been in
service for decades, and who knows who worked on it before you ...The L.O.
freq is 11.2 mhz ( on most Mastr II's, 9.4 on some) below your rx carrier
freq if you sniff near the mixer with a probe... This is the only true way
to set the mixer input ( which is what the crystal actually develops) . In
some cases you may need to tweak the L.O. if your I.F. cannot be set
perfectly at 11.2 due to old IF xtals which are not quite centered at 11.2
anymore or in some of the older versions, they were a lot less "tunable"
due to lack of tuning components...
In any case this sniffing procedure will tell you if your icom is
moving, as it is much easier to monitor the freq of a generated carrier (
L.O.) than to "guess" if the rx is centered in the I.F. pass...( at least
assuming you have a service monitor which is stable....)
You can also check your IF with a scope and a precision 11.2 mhz
source injected into the I.F. Input to I.F. stages...
I never have liked the written procedure that GE published on
Mastr II I.F. alignment. It could have been explained a lot better....
Doug
KD8B
At 10:47 PM 6/1/2005, you wrote:
>I have a GE Mastr II repeater on 444.325 +. The repeater was originally a
>VHF base station. I swapped out the RF modules, interfaced an outboard
>controller, and the other things to make it play. Or so I thought. I am
>using 2C ICOMS in the transmitter and receiver. The were redone by ICM.
>The Rx was sent back for them to repair after it wouldn't stay on freq. I
>got it back and thought all was ok. Earlier tonight, someone pointed out
>that it seemed the off frequency. The Tx is fine but the rx seems to be
>off. I haven't actually measure to see if it is but everbody sounds bad
>getting into it. Even the ham that lives 1/4 mile away. I was discussing
>this problem with another repeater owner here and he suggested maybe the
>comp line between the ICOMs was still connected and causing problems. The
>station originally had a 5C in the rx and an EC in the tx. Could this be
>causing problems? If so, can someone point me to the easiest was to break
>this connection? I don't have the complete manual here. I have tidbits of
>it in PDF but not the complete station/repeater manual.
>
>Thanks
>
>Jamey Wright
>KD4SIY
>444.325
>Wilson Mtn/Oden Ridge, Al
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