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Posted on Tuesday, April 09, 2002 - 11:33 pm:   Edit Post Delete Post    Move Post (Moderator/Admin Only)

Magnum 257

Complete specifications, modifications, and non-technical review.
*This review is good for models built before Mid-October, 2004

Frequency Coverage (10 Meter)28.000 – 29.699
Frequency Coverage (Expanded)25.165 – 29.699 (10 banks of 40 channels)
Antenna Impedance50 ohm, unbalanced
Frequency ControlDigital Phase-Lock Loop (PLL) Synthesizer
Frequency AccuracyBetter than +10 ppm from 0-40 degrees C after 15 min. warm up
Power Requirement12-13.8 V DC, negative ground
Current Consumption6 amps maximum
Dimensions6 X 2 X 9.5 in (W X H X D)
Weight2.9 lbs

Power OutputSSB / FM 30 Watts, AM 9 Watts Average, 30 Watts PEP
Tuning Steps1 kHz / 10 kHz / 100 kHz
Final Transistors2SC1969 (2)
Spurious EmissionsMore than 50dB below peak output power
Carrier SuppressionMore than 40 dB below peak output power
Unwanted SidebandMore than 50dB below peak output power (1 kHz tone)
FM Deviation+/= 2 kHz maximum
Audio ResponseMore than 30 dB below peak output
Frequency Response400 to 2800 Hz
Microphone ImpedanceECM, 600 to 1K ohms

Circuit TypeDual Conversion Superheterodyne
Intermediate Frequencies1st IF / SSB IF 10.695 MHz
2nd IF 455 kHz
SensitivitySSB - 0.25 V at 10 dB S+N/N
AM – 1.0 V at 10 dB S+N/N
FM – 0.3 V at 12 dB SINAD
SelectivitySSB – 4.2 kHz (-6 dB) / 8.5 kHz (-60 dB)
AM / FM - 6.0 kHz (-6 dB) / 18 kHz (-60 dB)
Clarifier Range+/- 1.5 kHz
Adjacent Channel RejectionBetter than 70 dB
IF RejectionBetter than 80 dB for all frequencies
Frequency Response250 to 3000 Hz
Audio Output power2 watts minimum at 10% THD with an 8 ohm load
Audio Output Impedance8 ohms


This is one of the simplest radios to mod, although you will need a soldering iron. To expand the transmit capabilities of this radio from 28.000 – 29.699 MHz to 25.165 MHz – 29.699 simply follow the steps below.

  1. Connect radio to power and turn on for 10 seconds.
  2. Turn off radio and disconnect power.
  3. Remove bottom cover.
  4. Remove (desolder) Diode D2 as shown in the picture. This is the only non surface mount component found there.
  5. Reset the radio’s processor by shorting the two circuit board pads as shown in the picture
  6. Connect power to the radio and turn it on.
  7. Push the FUNCTION knob “in” button, then press and hold the CALL button in until the band indicator appears on the LCD.
  8. Use the CALL button to select bands.
  9. To switch between channel number and the frequency, push in the FUNCTION knob and press the CALL button.


When the radio is turned off it will default to the 10-meter band. Simply press the LCR button to return to the last frequency you transmitted on prior to turning the radio off.

  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)
  5. Adjust RV4 for maximum modulation.
  6. Locate RV9. (SSB Power)
  7. Adjust RV9 for maximum forward power in SSB mode.
  8. Locate RV8. (RF Meter)
  9. With RF Output power knob adjusted to show a 5 watt carrier, adjust RV8 just until the 3rd RF power bar lights up.

Your Magnum 257 should now have a PEP output around 25 watts on AM and around 35 SSB.

Unfortunately I know of no other mods or tweaks for this radio. Keep and eye on the Copper talk Forum and I will keep you updated with any new information as it becomes available.

(1) MOD
(2) RX
(3) TX
(4) Ground - Channel DOWN, 2.2K ohm to Pin 3 - Channel UP

Let’s take a tour of the Magnum 257, so you can familiarize yourself with its controls and operation. I am not going to go into the entire operation of each feature, as it would be to complicated and take up too much space. You can download the entire owners manual will COMPLETE operating instructions at the Magnum Radio website. A link to that website is in the final comments of this review.


(1) MICROPHONE JACK Self explanatory although this radio does allow for the use of a microphone with UP / DOWN channel buttons to let you tune through the frequencies in each band without touching the radio. Another nice feature is the powered mic pin, which allows you to use a nice desk mic such as the ICOM SM-20. Be careful though, this pin is NOT current limited, so you can cause severe damage if you install a microphone incorrectly.

(2) MIC GAIN Allows you to adjust the level of modulation on the Magnum 257.

(3) RF GAIN Allows you to adjust the receiver sensitivity and level of received signals.

(4) STEP BUTTON /NB 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 (LAST CHANNEL RECALL) / RPT 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 The default call frequency is 29.300 MHz. Press this button to go to that frequency. This button is also used to program and recall Memory Channel #2.

(7) MODE / T. LOW 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 Lets you start scanning in 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 Allows for the programming and recall of one of the 5 user programmable memory channels. This radio will also remember MODE not just frequency.

(10) CLARIFER / FUNCTION Clarifier tracks on transmit and receive with a range of +/- 1.5 kHz. Pushing this knob in activates the FUNCTION mode to use the other features assigned to the buttons that I previously mentioned.

(11) FREQ Changes the operating frequency within the selected band.

(12) OFF / VOLUME Turns the radio on and off and allows for adjustment of volume.

(13) LCD DISPLAY Amber and backlit, it displays, frequency or channel, band, mode, S/RF meter, TX indicator, tone low, scan, repeater shift, NB, etc

(14) SQUELCH Self=explanatory

(15) PWR Allows for variable TX power. This feature works in both AM and SSB modes.

(16) PTT SWITCH Push to talk, release to receive.

(17) UP / DOWN Allows for the use of a microphone with UP / DOWN channel buttons to let you tune through the frequencies in each band without touching the radio.

PROGRAMMING TONE The audible tone sounds every time a button is pressed or the channel is changed via the microphone. To turn this off, power off the radio and then key the mic while turning the radio back on. To enable the programming tone, simply reverse this process.
MEMORY BACKUP The Magnum 257 will maintain its memory channels for up to 5 days without power to the radio.


Very low SWR.
5 Memory Inputs. Remembers Frequency and Mode.
Separate heat sink for driver and final transistors.
Mic plug has a powered pin (13.8 VDC) so desk mic such as the ICOM SM-20 may be used. Small size allows for easy mounting almost anywhere.
Very stable SSB.
Surface mount components.
Excellent audio, and capability of full power with stock microphone.
Very good value.

Display light bulbs burn out more frequently than I would like to see.
Radio automatically defaults to 10 meter band after power off. Although by pressing the LCR button you will go back to the last frequency you transmitted on.
Knobs have a lot of "play" in them.
Channel UP and DOWN buttons should be reversed in their placement on the mic.
Surface mount components.
Only a 5 digit frequency display rather than a 6 digit counter.
Will only allow tuning of frequencies within selected band.
When radio is at 60 degrees F or cooler the volume is very loud when the radio is turned on and cannot be lowered until the radio "warms up". This is a possible problem with the Volume Pot. Other instances of this have been recorded.

I have been waiting a long time to get my hands on one of these radios because I have heard great things about the Magnum 257, as well as the other radios in this line. Magnum International, a division of RF LIMITED, manufactures this radio in Korea. Their website can be found at Magnum Radio. As well as information on this particular model and other models in the Magnum line, you can also find the owners manual will full instructions at
Magnum 257 Manual

Let me say one thing about this radio. If you are going to buy one radio this year, buy a Magnum 257. If you are serious about quality sounding equipment, and excellent SSB DX performance, this is the radio you want. Finally there is a decent rig out there at an affordable price for the rest of us. By that, I mean, the rest of us who want serious 11 meter performance with sideband stability and without all the other noise toys that are so common in this realm of radio equipment. Affordable is a relative term, so I will put it in perspective. Less than $200 for all the features you want, and without all the stuff you don’t need. One other thing I will point out, is similar radios like the Eagle clones look the same but definitely lack the features and engineering of this particular radio. There is no comparison.

I would like to see a few things changed about this radio. Number one being the sloppiness in the knobs. The knobs work fine, but are loose and give the radio a cheap feel in that respect. Another would be the incorporation of the FUNCTION and CLARIFIER in the same knob. The tendency exists, with this setup, to knock yourself off frequency while trying to access other features of the radio.

The modulation is excellent. You don’t need a power mic on this radio, and full PEP output is easily attainable with the provided microphone. The mic is small and very much like some of the mobile VHF ham mics I have seen.

As a HR2510 user and devoted fan, this radio is the comparable radio to come along in a while. Easy to use, small, affordable and kicks butt on both AM and SSB. A very good choice for a novice or veteran radio operator. I highly recommend the Magnum 257.