Daniels MT-3 Manuale di istruzioni - Pagina 7

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G ENE R A L
The MT-3 Front End consists of a five pole
helical resonator filter structure with a single
stage, low noise, bipolar amplifier followed by
an image rejection filter and a double balanced
mixer. The highly selective narrow bandwidth of
the helical filter provides high out-of-band signal
rejection, high receiver spurious response, and
high wide band intermodulation attenuation. The
low noise amplifier increases receiver sensitivity
while the image rejection filter increases the
receiver's image frequency attenuation. After
filtering and amplification, the received signal
is down converted to 21.4 MHz by a double
balanced mixer. The MT-3 Front End is built in
a VHF (132 to 174 MHz) and two UHF (406 to
430 MHz and 450 to 470 MHz) versions. MT-3
Front End tuning over the respective frequency
ranges is done through helical filter adjustment
and image rejection filter selection.
Printed Copy Not Controlled
P O W E R A N D
I N T E R C O N N E C T I O N
The MT-3 Front End operates from +9.5 Vdc
applied via a short red wire connected to supply
point J6-2 on the receiver main IF/audio board.
Ground return is supplied via direct mounting
to the receiver chassis and coaxial cable
interconnections. The MT-3 Front End draws
approximately 8 mA from the IF/audio board's
+9.5 Vdc supply.
The RF input signal connected to the receiver
front panel type N connector is fed to the front
end SMB input connector (J1) by a short coaxial
cable. The MT-3 Front End's local oscillator
input and IF output are respectively routed by
coaxial cable from the local oscillator module
and to SMB connector J7 on the main IF/audio
board.
F I V E P O L E H E LI C A L F I LT E R
The received RF signal is filtered by a five pole
helical resonator band pass filter. This filter
provides front end selectivity and attenuates any
potential internally generated spurious signals.
Typically, the filter has an insertion loss of 3 dB
and a 3 dB bandwidth of 5.0 MHz in the VHF
range and an insertion loss of 4.5 dB and a 3 dB
bandwidth of 7.0 MHz in the UHF range. The
filter is tunable from 132 to 174 MHz for VHF
applications and 406 to 430 MHz or 450 to 470
MHz for UHF applications through adjustment of
the helical filter's five trimmer capacitors.
MT-3 Low Current Front End Instruction Manual
3
THEORY OF
OPERATION
IM11-FE3