Re: some text from a previous reply/post.
"I would find it unlikely that an oscillator would oscillate at two
different frequencies, however, it isn't impossible."
Actually quite probable.
As a Field Service Technician for the San Francisco, CA. Motorola Service
Station in the 80's. I sourced many multiple oscillation. One in
particular was a four frequency event from a solid state "narrow band
exciter" in a high rf environment. (Mt San Bruno)
This four frequency government base station (Motorola Micor) had pin
diode mode selection.
In the high RF environment, all the pin diodes would forward bias and
four frequencies made it out quite nicely to the 110 watt PA and through
to the antenna. High power excitement on four government frequencies at
one time....
"Just as an amplifier can have parasitic inductance and capacitance due
to lead
lengths, component placement, etc. so could a similar thing happen in an
oscillator circuit. An oscillator will oscillate at a frequency
determined by the resonance of the LC network (a XTAL oscillator works
EXACTLY the same with with the LC network being replaced by the XTAL). "
This is pretty much what happened with the Micor base station.
"However, if parasitic L's and C's exist that are not seen by the
fundamental oscillator yet do create a resonant circuit at another
frequency then it IS possible for a poorly designed oscillator to
oscillate at 2 different frequencies."
73,
Jon
KE9NA
Jon,
Motorola's oscillator is an excellent design, they just didn't anticipate
the power level in excess of one million watts within a small distance of
the circuit. Actual selection is done at a fundamental and multiplied up.
The multipliers and power amplifiers had no problem sending all four
right on through and out the door.
In relation to RF amplifiers. Motorola had a real nice VHF high power
paging transmitter amplifier which did a real nice job at UHF 450 and
900MHz. The dual 4CX250 model was never fixed, nor the cause mentioned.
It was quickly replaced with a revised amplifier chassis.
A similar problem in another VHF solid state amplifier turned up in the
MSR-2000 repeater amplifier. Lot's of spurs in lots of places. A "B"
revision also did the fix.
The MSR was a particular beast as the generated frequencies would often
move up and done in frequency with the heat of the pa board. We dubbed
it the "VFO amplifier."
I enjoy reading everyone's posts.
cheers
skip
nospam4me@juno.com
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