Magnum M-257 User manual

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S
SP PE EC CI IF FI IC CA AT TI IO ON NS S
Frequency Coverage 25.165 - 29.699 MHz
RF Power Output 30W SSB / 9W AM/ 30W FM
Dual Finals on Heat Sink
Modes AM, FM, USB, LSB
Microprocessor Controlled
5 memories
Last Channel Recall
Frequency Scan
10khz or 1khz steps
Variable RF Output Power
Variable Mic Gain
Built in Speech Processor
5 Digit LCD Frequency Display
Scanning Microphone
Night Illuminated Display
Surface Mount Technology throughout
Dimensions 2(H) x 6(W) x 9.5(D) in

GENERAL SPECIFICATIONS:
Frequency Coverage 28.000 to 29.699
Frequency Coverage
Expanded 25.165 – 29.699
Antenna Impedance 50 ohm unbalanced
Frequency Control Digital Phase-Lock Loop(PLL)Frequency Accuracy Better than +10ppm from
0-40° C after 15 min warm up.
Power Requirement 10.5 - 15VDC ~ Negative Ground
Current Consumption 6.0 amps maximum
Dimensions 6 x 2 x 9.5 in (W x H x D)
Weight 2.9 lbs.
TRANSMITTER SPECIFICATIONS:
Power Output SSB / FM ~ 30 Watts AM ~ 9 Watts Average / 30 Watts PEP
Tuning Steps 1kHz / 10kHz / 100kHz
Final Transistors 2SC1969 (x2)
Spurious Emissions More than 50dB below peak output power
Carrier Suppression More than 40dB below peak output power
FM Deviation +/- 2kHz maximum
Audio Response More than 30dB below peak output power
Frequency Response 400 to 2800Hz
Microphone Impedance ECM 600 to 1K ohms
RECEIVER SPECIFICATIONS:
Circuit Type Dual Conversion Superheterodyne
Intermediate
Frequencies 1st IF / SSB IF ~ 10.695 MHZ ~ 2nd IF ~ 455 kHz
Sensitivity SSB 0.25 V at 10dB S + N/N / AM ~ 1.0uV at 10dB S + N/N / FM ~ 0.3 uV
at 12dB SINAD
Selectivity AM/FM 6.0kHz (-6dB) / 18kHz (-60dB) / SSB 4.2kHz (-6dB) / 8.5 kHz (-
60dB)
Clarifier Range +/- 1.5 kHz
Adjacent Channel
Rejection Better than 70dB
IF Rejection Better than 80dB for all frequencies
Frequency Response 250 to 3000 Hz
Audio Output Power 2 watts minimum at 10% THD with an 8 ohm load

FREQUENCY MODIFICATION:
Step #1: Make sure Magnum 257 is turned off and disconnected from power source!
Step #2: Take off speaker-side cabinet.
Step #3: Find the CPU Reset Board located near the Front panel of the radio located behind the
Microphone Connector.
Step #4: On the CPU Reset Board there are 4 jumper positions (CON-1 / CON-2 / CON-3 / CON-4).
Each jumper position will provide a different frequency range and configuration.
From the list below, select the desired frequency range and configuration, and move the jumper shunt to
the corresponding CON #.
CON1: ~ 10 Meter Only (28.000 - 29.699 MHz)
*Default mode
*All functions operate normally
CON2: ~ 10 Meter & Expanded Mode
*At turn on, the radio defaults to 10 Meter mode.
*For Expanded mode, press FUNC and then press CALL for 3 seconds.
*To return to 10 Meter mode, repeat above steps.
for information on Expanded mode operation, see CON3
CON3: ~ Expanded Mode Only (25.165 - 29.699 MHz)

In the Expanded mode, the frequency range is divided into 10 Bands of 40 Channels each.
The Bands are shown on LCD display by letters (A through J) - Band E is regular 40 channel CB. To switch
bands, press the CALL button (do not hold down for 3 seconds).
In the Expanded mode, either the frequency or channel can be displayed on the LCD. To switch between
frequency display and channel display, press the FUNC button and then press the CALL button (do not
hold down for 3 seconds).
On the channel display, the small number (0 - 9) to the right of the Band letter is the 1 kHz frequency
display.
Example: If the frequency is 27.405, then the channel display will indicate 40 E5. (40) being the channel,
(E) being the Band, and (5) being the 1 kHz position of 27.405.
Note!
In the Expanded mode, the RPT and SHIFT functions Will Not Operate.
CON4: ~ 40 Channel CB Only (26.965 - 27.405 MHz) (Only operates on the regular 40 CB channels.)
Step #5 After selecting the desired frequency range and configuration, press the CPU Reset Switch (SW1)
for 5 - 10 seconds.
Step #6 Reassemble the radio, turn on and test.
TUNE – UP / POWER TWEAKS
#1 ~ Remove bottom cover
#2 ~ Locate RV16. (AM Power)
#3 ~ Adjust RV16 for a carrier of 10 watts on AM mode with the RF Power knob turned fully clockwise.
With the RF Power knob turned fully counter-clockwise, the AM carrier should be 1 watt.
#4 ~ Locate RV4. (Modulation)
Adjust RV4 for maximum modulation.
#5 ~ Locate RV9. (SSB Power)
Adjust RV9 for maximum forward power in SSB mode.
#6 ~ Locate RV8. (RF Meter)
With RF Output power knob adjusted to show a 5 watt carrier, adjust RV8 just until the 3rd RF power bar
lights up.
You should now see a PEP output of around 25 Watts on AM and around 35 Watts on SSB.

FRONT PANEL CONTROLS
#1 ~ MICROPHONE INPUT
Pin #1 ~ Microphone Audio
Pin #2 ~ Receive
Pin #3 ~ Transmit
Pin #4 ~ Down(Up w/22K Ohm Resistor)
Pin #5 ~ Ground
Pin #6 ~ +13.8VDC
#2 ~ MIC GAIN
#3 ~ RF GAIN
#4 ~ STEP BUTTON \ NB \ 1 STEP
Controls tuning steps in either 1 kHz, 10 kHz, or 100 kHz as well as activates the Noise Blanker circuitry
when used with the FUNCTION button. This button is also used to program and recall Memory Channel #1.
#5 ~ LCR \ RPT \ 4 LCR
Allows you to tune into the last channel you transmitted on. Also used to activate repeater splits when
used in conjunction with the FUNCTION button. This button is also used to program and recall Memory
Channel #4.
#6 ~ CALL \ 2
CALL The default call frequency is 29.300 MHz FM. Press this button to go to that frequency.
This button is also used to program and recall Memory Channel #2.
#7 ~ MODE \ T. LOW \ 5 MODE
Allows you to change the mode of transmission and receive AM/FM/USB/LSB. When using the FUNCTION
button you can also activate the Tone Low circuitry which acts as a roll-off for high frequency or “white
noise”. This button is also used to program and recall Memory Channel #5.
#8 ~ SCAN \ SHIFT \3 SCAN
Scans in increments 10 kHz steps. Also used to program repeater pairs\splits for FM repeater use. This
button is also used to program and recall Memory Channel #3.

#9 ~ M. SAVE \ M. LOAD
Memory Save and Memory Load (Recall)
#10 ~ CLAR \ FUNC
Clarifier shifts both the TX and RX frequency 1.5 kHz each side of the center frequency.
#11 ~ FREQ
Rotate clockwise or counterclockwise to select desired frequency.
#12 ~ OFF \ VOLUME
Turns the power to the radio on and off.
#13 ~ NONE!
THE FACTORY FELT THE NUMBER 13 WAS UNLUCKY!
(You will not find a Number 13 listed in the Owners Manual)
#14 ~ SQ
Squelch, Used to eliminate background or white noise and also used to activate the Scan feature (refer to
#8.
#15 ~ PWR
Variable RF Output Power.
#16 ~ Push to Talk Switch (PTT) SWITCH
Push to talk, Release to receive.
#17 ~ UP \ DN
Allows for Up and Down Frequency Control from the Microphone.
OTHER FEATURES:
#1 ~ PROGRAMING TONE
This tone sounds each time the CPU is being programmed. It is helpful, in the beginning so you can be
sure the command has been entered. You may eliminate the tone by simply pressing the PTT switch on
the microphone and turning on the ON/OFF POWER switch at the same time.
#2 ~ MEMORY BACK UP
The 257 features a super-capacitor back up for the 5 memory channels. The 257 can be disconnected
from a power source for approximately 4 or 5 days before the memory is lost.