AM SECTION
The MR66 delivers AM reception of the
highest possible quality. Four different AM
bandwidth/frequency response settings are
available. The NARROW setting provides
excellent selectivity and high noise rejection
for the weaker and more distant stations.
The MEDIUM 1, MEDIUM 2 and BROAD
settings provide progressively wider fre-
quency response for receiving the closer
more powerful stations.
In all but the BROAD setting a very sharply-
tuned whistle filter eliminates the 10KC
interference caused by adjacent-channel sta-
tion carriers. This highly-selective filter re-
duces the 10KC interference 60db (decibels)
below normal program level with no effect on
other audio frequencies.
Local AM reception at the BROAD and
MEDIUM 2 settings is of unusually high
fidelity and limited only by the quality of the
actual broadcast signal itself.
A double-tuned circuit at the input of the
RF amplifier increases selectivity while re-
taining the excellent AM bandwidth. The
antenna coils are connected with a rear
panel switch to allow perfect matching of a
convenient short loop antenna or a conven-
tional long lead antenna.
An amplified automatic VOLUME control
circuit maintains uniform volume output over
a wide range of station signal strengths.
Powerful local stations, as well as weak or
distant stations, are reproduced at an almost
equal volume level. The need for constant
volume adjustment during tuning is there-
fore eliminated.
Two IF amplifiers are coupled through a
low-distortion detector into a two-stage feed-
back amplifier. The output is low-impedance
and approximately equal in level to the FM
output. Level controls on the rear panel allow
you to exactly match the AM and FM output
volume levels.
GENERAL
A new type of mechanical tuning assembly
gives the MR66 extremely smooth flywheel
tuning. The tuning capacitors are driven
directly; the tuning capacitors, in turn, drive
the dial pointers. Backlash is practically
eliminated with this method of design.
A teflon-lined pointer carriage and nylon
pulleys reduce friction and wear to give an
unusually smooth and quiet dial action.
SPECIFICATIONS
FM CHANNEL
Sensitivity
3¼ microvolts at 100% modulation ( ± 75KC
deviation) for less than 3% total noise and
distortion in accordance with IHFM standards.
Distortion
Less than 0.8% at 100% modulation (±75KC
deviation), above 10 microvolts at antenna
terminals.
Audio Frequency Response
Within 2db from 20 to 20,000 cycles.
Capture Ratio
1 to 0.7
Muting
IF injected ultrasonic muting; 60db or more
noise reduction between stations.
Oscillator Drift
Less than 25KC with AFC disabled; negligible
with AFC in operation.
Image Rejection
Better than 80db at 90MC; better than
70db at 105MC.
Hum
Better than 65db below 100% modulation.
IF Amplifiers
Three (not including two limiters) with 200KC
bandwidth, flat-top response.
RF Amplifier
Cascode
Radiation
Substantially below FCC requirements.
Antenna Inputs
300 ohms balanced; 75 ohms unbalanced.
Output
Approximately 4 volts, low impedance.
2
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