FR-10
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6
oscillator of U1 from drifting away from an incoming signal. This is
accomplished by tuning the varactor circuit in the direction opposite the
drift.
The MC3359 IC has an internal oscillator controlled by the 10.24 MHz
crystal. The 10.24 MHz signal is mixed with the 10.7 MHz input from U1
to convert down to the low IF of 450 KHz. The 450 KHz IF is filtered by
FL2 and then amplified by a limiting amplifier in U2. Audio demodulation
takes place in the quadrature detector, with L4 adjusting the detector.
The audio modulation is detected in U2, and the background noise is
used to control the squelch. U3 amplifies the audio output from pin 10 of
U2 to a practical level for speaker or headphone operation. Pin 16 of U2
will ground the input of U3 when the squelch is closed.
L4, a 450 KHz IF coil, permits adjustment of the 90-degree voltage-
current phasing ("quadrature") of FL2's output to the FM detector
demodulator (pin 8 of the MC3359).
PARTS LIST
Inductors
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2 .33 uH inductors [looks like a resistor with 2 orange and 2 silver
bands] (L1,L2)
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1 slug-tuned coil [blue color] (L3)
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1 shielded transformer coil [marked LB 53303] (L4)
Semiconductors and IC's
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1 2SC2498 or 2570 transistor (Q1)
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3 2N3904 transistor (Q2,Q3,Q4)
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1 NE602 8-pin IC (U1)
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1 MC3359 18-pin FM receiver IC (U2)
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1 LM386 8-pin audio amplifier IC (U3)
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1 Varactor diode, MV2209 [looks like a transistor with two leads]
(D1)
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1 1N4148 signal diode (D2)
Special Components
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1 10.24 MHz Crystal (Y1)
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1 10.7 MHz ceramic filter [brown, molded, 3 leads] (FL1)
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1 450 KHz ceramic filter [black, square] (FL2)
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about 6 ma, how long will your battery last if you leave your receiver on
for a few days, just like we leave our computers and Ham or computer
accessories on all the time?
(2) We thought you'd have more fun planning and installing your own
lamp that glows in the dark!
(3) We could not decide which color you would like best!
THE RAMSEY ELECTRONICS CASE, KNOB & HARDWARE
OPTION
Your finished receiver can be installed in a variety of enclosures of your
own design and choosing. You might be planning to combine several
Ramsey circuit boards in a single enclosure. Use of the inexpensive
and attractive Ramsey case and knob kit will give your unit that finished
look and increase its resale value. These sturdy black instrument cases
are supplied with neatly-lettered front and rear panels, knobs, rubber
feet and mounting screws.
OTHER ENCLOSURE RECOMMENDATIONS
While we believe that the Ramsey enclosure and knob option is a fine
value for finishing off your Ramsey receiver or transmitter, we are happy
to give you a couple of additional suggestions. If your first goal is
economy and rugged portability, you will find that the circuit board can
be mounted nicely in a standard VHS videotape storage box, which also
gives room for a speaker, or earphone storage, and even a roll of
antenna wire. The controls are easily mounted at one end of such a box.
It may be necessary to cut away the molded posts which secure the
tape cassette itself. These storage boxes come in several styles, so pick
one that looks truly practical as a project enclosure.
To accomplish RF shielding, the most economical metal enclosure
nicely suited for Ramsey amateur kit boards is Radio Shack No. 270-
253A. This metal utility cabinet can accommodate both a receiver and
transmitter board, plus speaker, with room for various refinements you
might like to add.
FR-10 TROUBLESHOOTING GUIDE
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