Drake SP75 Service manual
TABLE OF CONTENTS
PAGE
General Description
I.
Specifications
II.
III. Installation
IV. Operation
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V. Theory of Operation
Alignment and Troubleshooting
VI.
VII. Service Data
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6
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III
ILLUSTRATIONS
Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Connecting SP75 to TR7 and PS7
Connecting SP75 to Systems Other Than
TR7 and PS7
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Phone Patch Connection
Tape Player Connection to SP75.
P. C. Board Pictorial, SP75
Fig. 6 Schematic, SP75
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to SP75
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I. GENERAL DESCRIPTION
The SP75 Speech Processor is designed to provide an increase in average
power and readability of a single sideband voice signal during weak signal or
high interference conditions. The SP75 is connected between the microphone
and microphone input of the single sideband transmitter, thus requiring no
modification of the existing transmitter or transceiver. A front panel switch
allows the processor to be switched in or bypassed as conditions warrant. Two
additional inputs, such as a tape player or phone patch, may be front panel
selected in place of the normal microphone input.
The amount of RF envelope clipping is adjustable between zero and twenty
decibels by a front panel control. A LED indicates proper audio input level.
Because of the pre-clipping audio compression, small changes in voice levels
do not widely affect the clipping level.
Muting circuitry reduces gain during speech pauses, thus reducing undesira-
ble background noise pickup and allowing VOX operation with the processor
on.
The SP75 was designed for optimum performance using the Drake model 7077
microphone and the Drake TR7 transceiver or Drake 4-line transmitters. How-
ever, excellent performance can be obtained with most other transmitters
which have a microphone input impedance of approximately 50 K ohm or
greater. Microphones other than the Drake 7077 may be used successfully.
However, microphones with a more sharply rising frequency response may
produce a less pleasant response than a microphone with a flatter response.
II. SPECIFICAT
Processing Type:
RF Clipping
Input Level (Microphone Input):
Range
ONS
Preclipping audio compression followed
by RF envelope clipping at the processor
intermediate frequency.
dB
Adjustable 0 to 20
control.
3.5
adjustable to
maximum.
minimum for full processing. Gain
mVV
accomodate
1
from front panel
up to 300
mV
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