Magnum M-257 - User Manual

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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

Summary

Product Overview and Specifications

General Specifications

Frequency Coverage

Specifies the operational frequency range of the transceiver, including an expanded mode.

Antenna Impedance

Details the required antenna impedance for optimal performance.

Frequency Control

Explains the method used for frequency control and its accuracy.

Power Requirement

Outlines the voltage and polarity needed for the device.

Dimensions

Provides the physical size of the transceiver.

Transmitter and Receiver Specifications

Transmitter Power Output

Details the RF power output for different modes (SSB, AM, FM).

Transmitter Tuning Steps

Specifies the increments for frequency tuning.

Receiver Sensitivity

Indicates the minimum signal level required for reception.

Receiver Selectivity

Defines the receiver's ability to distinguish signals.

Receiver Clarifier Range

Specifies the adjustment range for fine-tuning received signals.

Frequency Modification Procedures

Frequency Range Configurations

Details jumper settings for different frequency coverage modes.

Tune-Up and Power Tweaks

Guides for adjusting RF power and modulation for optimal performance.

Front Panel Controls Overview

Microphone Input and Mic Gain

Details pin assignments for the microphone and mic gain adjustment.

RF Gain and Step Button

Explains RF gain control and the function of the step/NB button.

LCR, RPT, CALL, and MODE Buttons

Describes functions for last channel recall, repeater use, call frequency, and mode selection.

Scan, Shift, Freq, and Clarifier Controls

Details scan, shift, frequency selection, and clarifier functions.

Volume, Squelch, and Power Controls

Explains volume, squelch, power controls, and variable RF output power.

Push to Talk and Microphone Controls

Details the PTT switch and microphone UP/DN controls.

Other Features and Functions

Programming Tone and Memory Backup

Describes the programming tone confirmation and memory channel backup system.

Overview

1. Function Description
2. Important Technical Specifications
3. General Specifications
4. Transmitter Specifications
5. Receiver Specifications
6. Usage Features
7. Front Panel Controls
8. Microphone Controls
9. Frequency Modification
10. Maintenance Features
11. Tune-Up / Power Tweaks
12. Other Features

The Magnum M-257 is a 30W AM/FM/SSB 10-11 Meter Mobile Transceiver, designed for mobile communication with a focus on a wide frequency range and multiple transmission modes. It is priced at US$250.00 ex stock Jakarta, with availability expected in the second week of March.

Function Description:

The transceiver operates across a broad frequency spectrum, supporting AM, FM, USB, and LSB modes. It is microprocessor-controlled, offering features like 5 memory channels, last channel recall, and frequency scanning. The device includes a scanning microphone for convenient operation and a night-illuminated display for visibility in low-light conditions. Its surface mount technology contributes to a compact design and potentially improved reliability.

Important Technical Specifications:

General Specifications:

• Frequency Coverage: The standard coverage is 28.000 to 29.699 MHz. An expanded mode extends this to 25.165 to 29.699 MHz.
• Antenna Impedance: 50 ohm unbalanced.
• Frequency Control: Digital Phase-Lock Loop (PLL) ensures frequency accuracy better than +10ppm from 0-40°C after a 15-minute warm-up.
• Power Requirement: 10.5 - 15VDC, negative ground.
• Current Consumption: 6.0 amps maximum.
• Dimensions: 6 x 2 x 9.5 inches (W x H x D).
• Weight: 2.9 lbs.

Transmitter Specifications:

• Power Output: 30 Watts for SSB/FM, and 9 Watts Average / 30 Watts PEP for AM.
• Tuning Steps: Selectable 1kHz, 10kHz, or 100kHz steps.
• Final Transistors: Equipped with two 2SC1969 transistors.
• 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.
• Built-in Speech Processor: Enhances audio clarity.
• Variable RF Output Power: Allows adjustment of transmission power.
• Variable Mic Gain: Provides control over microphone input sensitivity.

Receiver Specifications:

• Circuit Type: Dual Conversion Superheterodyne.
• Intermediate Frequencies: 1st IF / SSB IF ~ 10.695 MHz, 2nd IF ~ 455 kHz.
• Sensitivity:
  • SSB: 0.25 µV at 10dB S + N/N.
  • AM: 1.0 µV at 10dB S + N/N.
  • FM: 0.3 µV 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.

Usage Features:

Front Panel Controls:

• Microphone Input (Pin #1-6): Standard 6-pin connector for microphone audio, receive, transmit, down/up (with 22K Ohm Resistor), ground, and +13.8VDC.
• MIC GAIN (#2): Adjusts microphone input sensitivity.
• RF GAIN (#3): Controls receiver RF gain.
• STEP BUTTON \ NB \ 1 STEP (#4): Controls tuning steps (1 kHz, 10 kHz, 100 kHz) and activates the Noise Blanker circuitry when used with the FUNCTION button. Also used for Memory Channel #1 programming/recall.
• LCR \ RPT \ 4 LCR (#5): Tunes to the last transmitted channel, activates repeater splits with FUNCTION button. Also for Memory Channel #4 programming/recall.
• CALL \ 2 (#6): Accesses the default call frequency (29.300 MHz FM). Also for Memory Channel #2 programming/recall.
• MODE \ T. LOW \ 5 MODE (#7): Changes transmission/receive mode (AM/FM/USB/LSB) and activates Tone Low circuitry (roll-off for high frequency/white noise) with FUNCTION button. Also for Memory Channel #5 programming/recall.
• SCAN \ SHIFT \ 3 SCAN (#8): Initiates scanning in 10 kHz steps, programs repeater pairs/splits for FM repeater use. Also for Memory Channel #3 programming/recall.
• M. SAVE \ M. LOAD (#9): Saves and recalls memory channels.
• CLAR \ FUNC (#10): Clarifier shifts TX and RX frequency 1.5 kHz each side of the center frequency.
• FREQ (#11): Rotary knob to select desired frequency.
• OFF \ VOLUME (#12): Turns power on/off and controls volume.
• SQ (#14): Squelch control to eliminate background noise, also activates the Scan feature.
• PWR (#15): Variable RF Output Power control.

Microphone Controls:

• Push to Talk Switch (PTT) SWITCH (#16): Engages transmit mode when pressed, receives when released.
• UP \ DN (#17): Allows for up and down frequency control from the microphone.

Frequency Modification:

The transceiver supports frequency modification via a CPU Reset Board located near the front panel. This involves moving jumper shunts (CON-1 to CON-4) to select different frequency ranges and configurations:

• CON1 (Default): 10 Meter Only (28.000 - 29.699 MHz). All functions operate normally.
• CON2: 10 Meter & Expanded Mode. Defaults to 10 Meter mode on power-up. Expanded mode is accessed by pressing FUNC then CALL for 3 seconds.
• CON3: Expanded Mode Only (25.165 - 29.699 MHz). In this mode, the frequency range is divided into 10 Bands (A-J) of 40 Channels each. Band E is the regular 40-channel CB. Bands are switched using the CALL button. The display can show either frequency or channel, toggled by FUNC then CALL. The RPT and SHIFT functions are not operational in Expanded mode.
• CON4: 40 Channel CB Only (26.965 - 27.405 MHz). Operates only on regular 40 CB channels.

Maintenance Features:

Tune-Up / Power Tweaks:

The manual provides instructions for adjusting power output and modulation:

1. Remove bottom cover.
2. Locate RV16 (AM Power): Adjust for 10 watts carrier on AM mode with the RF Power knob fully clockwise, and 1 watt when fully counter-clockwise.
3. Locate RV4 (Modulation): Adjust for maximum modulation.
4. Locate RV9 (SSB Power): Adjust for maximum forward power in SSB mode.
5. Locate RV8 (RF Meter): With the RF Output power knob set to show a 5-watt carrier, adjust RV8 until the 3rd RF power bar lights up. This should result in approximately 25 Watts PEP on AM and 35 Watts on SSB.

Other Features:

• Programming Tone: A tone sounds each time the CPU is programmed, confirming command entry. This tone can be eliminated by pressing the PTT switch on the microphone while turning on the ON/OFF POWER switch.
• Memory Back Up: The 257 includes a super-capacitor for backing up the 5 memory channels. This allows the unit to be disconnected from a power source for approximately 4 to 5 days before memory data is lost.

Magnum M-257 Specifications

General

Brand	Magnum
Model	M-257
Category	Transceiver
Language	English