Atlantic
TECHNICAL DESCRIPTION
Page 1
A). GENERAL DESCRIPTION
The Atlantic Marine radio is a self-contained transceiver unit with integral
antenna intended for use as a general communication tool. The useable range,
while dependent upon terrain and other radio propagation principles, is
typically five miles. The Atlantic uses the maximum transmit power allowed to
help ensure the maximum communication range.
Features include: Channels, 10 channels Weather radio, Channel
Monitor, Page and LCD Display. The unit is equipped with an external
Headset option connector. Four AA alkaline batteries that are readily
available in retail outlets supply operating power. An automatic power savings
feature allows the typical standby battery life to extend to more than 10 days.
B). FREQUENCY DETERMINING CIRCUITS
The fundamental frequency for both the transmitter and the receiver
local oscillators are controlled by a phase lock loop (PLL) circuit IC201
(Toshiba TB31202, or equipvalent). The frequency of operation of the FRS
voltage controlled oscillator (VCO), composed of Q301 and Q302 operating in
cascade is phase locked to a voltage controlled crystal reference (VCXO)
operating at 20.95MHz (X202).
The VCO is locked to the fundamental of the transmit signal in the transmit
mode and is locked to the receive 1
st
LO (Fundamental channel frequency
minus 21.4MHz) in the receive mode. The crystal reference frequency is
shared with the 2
nd
LO of 20.95MHz.
C). TRANSMITTER CIRCUITS
The transmitter amplifies the 0 dBm signal from the VCO to
approximately 27dBm that is fed to the antenna. The transmitter is a three
stage amplifier composed of Q1,3,4 and Q11. The first two stages are
operated class A and the final is operated class B in full saturation to help
prevent unwanted amplitude modulation. The fundamental transmit signal is
fed through an elliptical low pass filter (5-pole, 2 zero) in order to suppress the
harmonics to below –50 dBc. The desired frequency modulation of the carrier
is accomplished by modulating the current in the VCO directly with the
microphone audio signal. The microphone audio is conditioned with a three-
pole high pass filter at 300 Hz (IC5C,D), a hard clipper circuit (IC5B) to limit
maximum deviation to +/- 2.5 kHz and a three-pole low pass or splatter filter at
2.8 kHz (IC5A
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