www.mentorradio.com
Phone: 216-265-2315 * Fax: 216-267-2915
M15-OM-11/11
INTRODUCTION
The Mentor Model M15 receives and transmits on up to six discrete channels in the vhf aviation
band between 118 and 137 MHz (25 KHz channel spacing). It operates from a 14 v dc supply, and is
intended for both vehicular and airborne application as well, and can also be used as a base
station. Its advanced design features and surface mount construction provide compactness, light
weight and high reliability. The only external components required are a suitable antenna with
coaxial cable, an aviation-type microphone and a 4- or 8-ohm speaker.
CIRCUIT DESCRIPTION
The receiver is a single-conversion superheterodyne with four varactor-tracked RF tuned circuits
and dual-gate MOSFET transistors in the RF amplifier and mixer stages. The local oscillator uses 3rd
overtone crystals, and is followed by a MOSFET frequency tripler stage. Receiver selectivity is
primarily determined by a six-pole 10.7 MHz crystal filter connected between the mixer and I.F.
amplifier. The latter consists of two cascode integrated circuit amplifier stages. Automatic gain
control is applied to the RF amplifier and the first I.F. amplifier stages.
A conventional diode detector is followed by a noise limiter, audio amplifier, squelch “gate” and
an integrated circuit audio power amplifier capable of delivering 4.5 watts of audio power into a 4-
ohm speaker. The transmitter oscillator also uses 3rd overtone crystals, followed by varactor
tracked MOSFET tripler and buffer amplifiers. Three untuned broadband stages boost the
transmitter carrier power to approximately 5 watts. Amplitude modulation is applied to the last
two stages, the "driver" and “final” amplifiers.
The transmitter signal passes through a 7-element Tchebychef low-pass harmonic filter which also
contains two PIN diodes functioning as a T-R switch. The transmitter modulator is separate from
the receiver audio amplifier, and includes an audio AGC amplifier that automatically adjusts for
variations in operator “microphone technique”. This circuit also prevents overmodulation.
The modulator power amplifier consists of an integrated circuit amplifier followed by
complementary bipolar transistors. This arrangement eliminates the need for an audio transformer,
resulting in less low frequency distortion while minimizing the size and weight of the radio.
The 25 watt RF transmitter power amplifier contains a single mosfet power transistor, operating
class AB, on a microstrip type printed circuit board. Two internal relays operate when the push-to-
talk microphone switch is pressed. These relays switch the amplifier’s input and output
connections, so that in the receive mode the signal from the antenna is passed directly back to the
M15’s receiver, while in the transmit mode the M15’s transmitter output is applied to the 25 watt
amplifier, whose output is in turn connected to the antenna. The power amplifier also contains a 5
section low-pass filter that greatly attenuates transmitter harmonics so that the system meets FCC
requirements for signal purity.
Содержание M15
Страница 7: ......
