Magnum 257HP 10 Meter AM/FM/SSBExport Review

Before you begin reading this article I will give a little disclaimer: I did use some of the paragraphs from the Omegaforce and Deltaforce articles in this review since these three radios do share some of the same features. Rather than wasting time re-writing the same info to sound different, I thought I’d focus on writing about what sets this radio apart from the others.

he new Magnum 257 HP

It’s hard to believe it’s been seven years since I owned my first amber display Magnum 257. At the time I had purchased one brand new on eBay for $169. When I received the radio I did the expanded frequency conversion (which was a little difficult on the older models), added the NPC modification, and turned up the microphone gain via the small potentiometer located inside the microphone.

The original Magnum 257

I was rewarded with a very solid performing SSB export radio that I used in my mobile all over the Northwest United States and I took the radio with me when I moved to Hawaii. Originally the radio was paired with a KL203 amplifier and I made DX contacts from Africa to Chile.

Fast forward to today.

In front of me I have the latest version of the Magnum 257, the Magnum 257 HP, and while it still retains much of my original radio’s looks there have been some significant changes since 2003.

The original Magnum 257 was a dual final radio with 1969 final transistors and was capable of around 25-30 watts PEP. The display was amber in color and the radio was very popular for SSB but many people faulted its AM performance as not being loud enough.

The NPC mod for the 257 was introduced shortly after, which allowed the radios to have much louder AM audio, especially if you also made the adjustment to the VR pot inside the stock microphone.

Magnum made changes to the radio in 2004-2005 and it then came with dual ERF-2030 transistors and was capable of roughly 40 watts PEP (it was advertised as 50 watts PEP). The new radio then came with a blue display and Magnum also started including Top Gun technology on the radios by adding the Top Gun Compressor.

With the Top Gun compressor installed on the Magnum 257 the NPC mod was no longer necessary as the radio now had very solid audio on both AM and SSB. The compressor helped maintain consistent audio peaks and provided the Magnum 257 with very consistent audio with even more punch than previous versions.

The latest version of the Magnum 257 (the HP) takes the current version to the next level with the addition of the new RFX 75 final system from RF Limited, giving the radio output in the 70-80 watt range.


When you see the new Magnum 257 HP box you’ll notice they are still shipping them in the old style original Magnum boxes showing the radio with the yellow display (I think Magnum must have a ton of the old boxes around since it’s been five years since the changeover to blue). The features shown on the box are all correct though and point out all the advanced functions of this radio. Make note that the PEP output is incorrect (shows 30 watts on the box) and if you are buying the radio and want to make sure you are getting the new HP version look for the sticker in the upper right hand corner that says 257HP.

When you open the box you’ll be greeted by the smallest SSB export radio on the market. Even after owning my original yellow model and the later blue face models I’m always impressed by just how compact this radio really is.


When talking about the size of this radio you’ll hear everyone say how compact it is, but I think a picture really is necessary to give people a better idea of the size of this radio.

In the picture below with the Magnum 257 HP you’ll see two SSB radios I had on my bench: a Uniden 640e (one of the smaller SSB CB radios around) and the Cobra 140 GTL (smaller than the Cobra 148, Galaxy 959, etc.). Keep in mind the two CB radios shown are single final radios that only will do around 20 watts max and don’t have near the number of features available on the Magnum 257.


The following knob controls can be found on the Magnum 257 as specified in the owners manual. Many of these functions may change or will be disabled in expanded frequency mode.


    OFF: Turns the power to the radio on and off

    VOLUME: Adjusts the AF gain, or volume of the received audio. Turn clockwise to increase and counterclockwise to decrease.

  • RF GAIN CONTROL: Adjusts the receiver sensitivity to both signals and background noise. This affects the distance at which a signal can be detected. Turning the control counterclockwise reduces the receiver sensitivity. This is particularly useful in areas where large volumes of traffic (signals) are present. The S/RF display indicates the received signal’s strength. The S/RF display is the bar graph located on the lower edge of the LCD screen.


  • MICROPHONE GAIN CONTROL: Increases or decreases the energy developed in the microphone amplifier circuit. The gain increases as the control is rotated clockwise. For optimum setting, press the push-to-talk (PTT) switch on the microphone, adjust the mic gain control until all segments of the S/RF display are lit. Next, rotate the control counterclockwise until the last segment of the display starts to flicker. The S/RF display is the bar graph located on the lower edge of the LCD screen.


  • SQ: Squelch. Used to eliminate background or “white” noise when monitoring strong signals. Also used to activate SCAN feature. To properly adjust squelch circuit, start rotating the control slowly clockwise until the received white noise disappears.
  • PWR: Variable RF Output Power. Rotate clockwise to increase RF output power. Rotate counterclockwise to decrease RF output power. Variable RF output power allows low power transmitting for QRP operation in compliance with the FCC request for reduced signal strength during periods when propagation levels are high.

    CLAR: Clarifier. The clarifier shifts both the TX and RX frequency 1.5 kHz each side of the center frequency. This is necessary for tuning to an SSB signal. Rotate the clarifier control clockwise or counterclockwise to tune an SSB signal.

    FUNC: Function. This control is used to operate the six control buttons on the front panel that are printed in blue. Press slightly and release, FUNC will be displayed on the LCD indicating that the function command is activated. After you have pressed one of the buttons the FUNC will disappear from the screen.

  • FREQ: Frequency. Rotate clockwise or counterclockwise to select the desired frequency.

Operating some of the features require the use of the function control. To activate the function control, momentarily push the FUNC (10) control, the FUNC prompt will be displayed in upper left-hand corner of LCD. Push the control again to deactivate the function control.

  • STEP: Tuning Step. The STEP control selects frequency resolution in either 1 kHz, 10 kHz or 100 kHz steps. Press the STEP button, one of the digits will flash on and off. Press the STEP button again to change stepping resolution. To tune frequencies in either 10 kHz or 100 kHz increments, press the STEP button until the desired digit is flashing. Rotate the FREQUENCY control in either direction. The entire frequency range of the Magnum 257 can be stepped through in 10 or 100 kHz increments. To tune in 1 kHz increments, press the STEP button until the 1 kHz digit flashes on and off. Rotate the FREQUENCY control. NOTE: When stepping in 1 kHz increments, you are limited.
  • NB: Noise Blanker. Noise blanker on and off control. This circuit eliminates pulse type interference usually associated with automotive ignition systems. To activate the noise blanker, press the FUNC control and then press the NB button. NB will appear on the LCD indicating the noise blanker is turned on. To turn off the noise blanker, repeat the same process.
  • CALL: The call button allows the radio (once converted) to jump through the different bands of frequencies. It uses the common A, B, C, D..etc type system to identify which grouping you are currently using. In 10 meter mode it brings up the the call frequency – 29.300 MHz, FM. The radio’s operating frequency and mode are automatically reset to this when the CALL button is pressed.
  • SCAN: Frequency Scan. Scans in increments of 10 kHz. There are two ways to scan using the front panel controls. (1) Receive Audio On Scanning: Press the SCAN button. Scan rate is one step every 5 seconds. To stop scanning press the SCAN button again, or momentarily press the PTT button on the microphone (scanning will stop without transmitting).(2) Receive Audio Mute Scanning: Carefully rotate the squelch control a minimum excursion (refer to 14) until the receive audio is off. The receiver scan rate will now be five frequencies per second. When a signal is detected the squelch is automatically disengaged and the scanning is paused. The squelch circuit will automatically re-engage and the receiver will continue to scan the moment the received signal is no longer detected. To stop scanning, press the SCAN button, or momentarily press the PTT button on the microphone (scanning will stop without transmitting).
  • SHIFT: Shift Offset. Used for programming offsets to operate repeater networks. The 257 can transmit and receive on different frequencies. To program the offset, press the FUNC button and hold down the SHIFT button for 3 or more seconds. Three digits will appear on the LCD. This is the offset frequency in kHz. Rotate the FREQUENCY control until the desired offset frequency is displayed. To return to the main display press the FUNC button and hold down the SHIFT button for 3 or more seconds, or momentarily press the PTT button on the microphone (the transmitter will not be engaged). To activate the programmed offset frequency, press the FUNC button, and then press the SHIFT button once. +SHIFT is displayed on the LCD. The 257 will now transmit on the frequency that is XXX kHz greater than the displayed, or receive, frequency (XXX represents the programmed offset frequency in kHz). To transmit on the frequency that is XXX kHz lower than the displayed, or receive, frequency press FUNC, then the SHIFT button. Repeat this until -SHIFT is displayed on the LCD. To disengage the programmed offset frequency, press the FUNC button and then press the SHIFT button. Repeat this until the SHIFT indicator is no longer displayed on the LCD.
  • LCR: Last Channel Recall. Press the LCR button to return to the last frequency that was transmitted on for more than 3 seconds.
  • RPT: Repeater Access Tone. Most repeaters require an 88.5 Hz tone burst to access. To activate the 88.5 Hz tone burst, press the FUNC control and then press the RPT button. RPT will appear on the LCD indicating that the tone burst will now automatically be transmitted whenever the PTT is pressed. To deactivate, repeat the same process.
  • MODE: Operating Mode. Press the MODE control to select the operating mode. The operating mode is indicated on the liquid crystal display: AM, FM, USB, or LSB.
  • TONE LOW: Press the FUNC button, and then press the T. Low button to turn on the receive audio tone control. LOW will appear on the LCD when thelow tone is activated. This feature will roll-off high frequency noise (i.e. “white” noise). Under many operating conditions this will improve the clarity and understanding of received signals.
  • M.SAVE: Memory Save. To save in memory a specific frequency and operating mode, select the desired mode and rotate the FREQUENCY control to the desired frequency. Press the FUNC button, and then press the M.SAVE button. S will appear on the LCD next to the frequency. While S is displayed, immediately press any of the memory channel buttons (1 – 5). The mode and frequency is now saved into memory. If the S indicator disappears before you press the memory channel button, the information will not be saved and the process must be repeated.
  • M.LOAD: Memory Load (Recall). To load, or recall, any of the saved memory channels press the M.LOAD button. L will appear on the LCD for several seconds. While the letter is displayed press the desired memory channel button (1 – 5). The programmed mode and frequency will be displayed.



  • Mode, Call, and Memory Channel buttons

While most export radios require you to flip band switches A through F or use hi/lo buttons to access all the frequencies, the Magnum 257 HP has a microprocessor which allows you to flip through the bands with the push of the “call” button. Instead of having to flip an AM, FM, USB, LSB, CW switch back and forth it has a “mode” button which provides this function.

The memory channel button feature is perhaps my favorite feature of all. This radio has five dual use buttons which can be used to store your favorite frequencies (something also found on the Deltaforce and Omegaforce). Not only can you store the frequency but it also stores the mode (AM,FM,LSB,USB,CW) that you want to use on that frequency. I’ve talked in other reviews about how much I enjoy using radios with this ability. You can jump from 27.455 LSB to 27.185 AM or 28.4000 USB with just the push of a couple of buttons and with practice it only takes seconds. On radios like the SS-158EDX the same change would require you to change the band knob, the mode knob and then use the channel selector to move through the channels.

  • Variable Power

This feature is becoming common on just about every export radio on the market, but there was a time when many radios did not have this ability. The variable power on the Magnum 257 HP allows you to set the radio to a low deadkey for running an amplifier or a high setting for running barefoot.

At the back of the radio you’ll see the RFX 75, power cord, antenna connector, and ext speaker jack. Note that the Magnum 257 HP does not have a PA function. Also you’ll notice that this radio uses a different style quick disconnect than was used on the original versions.


The RFX 75 is a unit designed and sold by RF Limited (Magnum) and can be added to most CB and export radios on the market. Magnum is installing these on the new high power Magnum 257 HP at the factory.

Originally the Magnum 257 radio used dual 1969 finals which were good for about 30 watts and then later they used dual ERF2030 finals which would produce 40 watts. The new RFX 75 uses an ERF2030 transistor driving a newly released ERF7530 transistor. The ERF7530 is rated at 50 volts 9.5 amps 80 watts output and is described by Sam Lewis, owner of Magnum Radios, as a very “rugged” transistor rated at greater amperage and capable of handling higher standing wave than previous transistors.

On radios like the Cobra 29 that use a modulation transformer it’s possible to see 100+ watts PEP when a RFX 75 unit is installed, while on radios like the Magnum 257 HP that use Audio Amplifiers (2SB817) expected output will be in the 70 watt range, depending on how the radio is tuned.

When testing this new high power Magnum 257 HP I did do some long talking and I noticed that when using high power that the heat sink will get what I would consider to be very warm. After some long conversations with the radio at max output it was almost too hot to touch. If you are a long talker I would suggest adding a fan to the RFX75 section just for extra cooling.

When running these radios as a base unit Magnum recommends the Astron 20 amp power supply.


The Top Gun Compressor is included in the “S” series radios and is also now included in the Magnum 257 radio. The Top Gun Compressor works in AM, FM, and SSB modes, keeping the modulation at peak performance in all these modes. This technology has been around for quite some time and was developed by the same people who came out with the SPA-1 speech processor.

Magnum has an exclusive agreement with the manufacturers of the Top Gun technology and their radios are the only ones which include these components from the factory.


Converting this radio for expanded coverage requires removing the radio covers, locating a small board inside the radio and then moving a plastic jumper to a different set of pins. The instructions for converting this radio can be found (HERE)

 Board mounted inside radio with jumper on opposite side.

Stock radio jumper position “CON 1”.

 Jumper moved to “CON 3” for expanded coverage


A surprising feature for these radios comes packaged inside the microphone itself. While most radios on the market come with simple stock microphones, the Magnum 257 HP includes an amplified 6 pin microphone that is powered by the radio. The microphone also has up/down controls on the front of the radio for changing frequencies via the microphone. This is a very nice feature for use in the mobile so you don’t need to take your eyes off the road or touch the radio to change frequencies.

The power microphone has an adjustment inside so not only can you adjust the microphone gain on the radio you can also turn up the gain at the microphone. These microphones are quite loud and offer good audio response. I’ve tested these previously against D104M6B microphones and found they were just as loud and sounded better for my voice than the D104.

To adjust the gain inside the microphone you need to remove two screws on the back cover, remove the cover, and then pull out the small board that is recessed in the inside front microphone section. There is a potentiometer on this board that provides the adjustment.



  • Receive

The Magnum 257 HP is known for having a very sensitive receiver. The Magnum 257 HP can pick up far off stations very well even when conditions aren’t great. On my base setup I found the receiver to be excellent for talking local and DX and noticed that many local stations who were often hard to hear were more understandable when I was running this radio.

Now the bad part of this sensitive receiver is that in addition to picking up far off stations it also likes to pick up electrical interference better than other radios. In a mobile install you’ll notice this radio does pick up electrical interference from power lines, neon signs, and other electrical sources with more noise than many other more standard CB’s. The NB/ANL function definitely can help in reducing some of the extra fuzz you’re bound to pick up with this radio.

And while one could complain about a radio with such a “hot” receiver, I have to say that even with the extra noise the radio picks up signals so well that you quickly forget your complaints.

  • Modulation

We recently did a review on the Magnum Omegaforce and it’s a very loud AM and SSB talking radio. While the Magnum 257 HP isn’t going to be quite as loud I can say I was very surprised at how well the Top Gun Speech compressor in this radio keeps the audio levels up. While the original Magnum 257’s required modifications to bring up the AM audio, the new Magnum 257 HP’s can give you very solid AM audio right out of the box. (Listen to the AM Audio on YouTube). This radio only has the Top Gun Compressor while the “S” models in the Magnum line have both the compressor and modulator.

The other thing you’ll find with the Magnum 257 HP is that the audio is very clean. Some people who are used to crunchy audio might mistake this as not being as loud as their tweaked and peaked Galaxy 99V, but I found this radio to have plenty of audio for both AM and SSB modes.

  • Output

The RFX 75 on this radio definitely gives it a leg up on the original, and puts its output at 30-40 watts higher than most other standard exports on the market. The extra wattage can make a big difference locally and the 70 watts this radio can do is the perfect amount for SSB DXing.

During testing I did some internal tweaks and managed to get the radio to hit around 80 watts SSB but the RFX 75 heated up very fast. I turned the radio back down and let it run around 70 watts with good results. As the RFX 75 gets warm you will see a drop off in wattage. Roughly around 5-10 watts. After hour long use I found the radio peaking around 60-65 watts.

  • SSB Stability

Magnum 257 HP’s use a microprocessor controlled TX and RX system which helps prevent frequency drift. Much like the RCI-2950DX, Uniden HR2510, and Magnum Omegaforce these radios are super stable on SSB and give excellent performance.


While this radio has plenty of features and great performance there are a couple of points that I thought should be brought up –

  • Unlocked clarifier

The original Magnum 257 had a locked clarifier (adjusted RX frequency only). The new Magnum 257 HP clarifier does control both your TX and RX frequency so you can easily tune by ear to where you want to transmit. Many people really like this feature but I still prefer the original locked clarifier. If the display on this radio was an actual frequency counter I wouldn’t mind having an unlocked clarifier.

  • Frequency display isn’t a frequency counter

While the LCD readout can be set up to show either a channel readout or frequency readout, the frequency display doesn’t show your actual receive and transmit as you control or change it with the clarifier. Now while this might be a negative to some people, this radio has very little to no drift so staying on frequency isn’t an issue. If you’re someone who likes to see when you change your clarifier from 27.3850 to 27.3851 then you may not like this type of display. On the plus side though you can use the step button to control the frequency. So if you want to go from 27.3850 to 27.3800 you can do so using the step button.

  • Electrical noise when mounted in a vehicle

There’s been discussion for quite a while about the Magnum 257 and that it picks up more noise in many mobile installs than other radios. Generally this statement is correct, but as I mentioned above, part of the reason there is more noise is that the Magnum 257 has a better receiver than many other radios. If you live in a large city and are surrounded by neon signs, stoplights, and above ground power lines than the Magnum 257 HP might not be the perfect radio for you, something like the Magnum S-9 is going to have better noise blanking abilities.

While I’ll say I did notice a little more noise than my other radios, I easily heard transmitting stations during my mobile testing. I ran the original Magnum 257 for many years in my mobile without issue and the new model definitely seems a bit quieter. During busy DX this last week the radio picked up stations so well I didn’t even notice the electrical noise, only the DX. The only times I really was aware of this radio being a bit noisy was driving right through the downtown of the city late at night when no one was on the radio.


**Please note – the use of this radio on Amateur radio frequencies is limited to operators who have a valid Amateur radio license. If you do not have a ham radio license DO NOT operate this radio on ham radio frequencies. The CB band is from 26.965 to 27.405, if you intend to use the Magnum 257 HP as a CB radio (illegal according to FCC rules) do not operate outside of those frequencies as you may be interfering with vital emergency or military communications.

While some ham radio operators will cringe at the thought of anyone using an “export” radio on the ham bands, certain models can perform quite well if set up properly. The RCI-2950DX, HR2510, 2600, Lincoln, and Magnum 257 have all been used on ham frequencies with positive results. While there continues to be a huge amount of backlash from the ham radio community regarding export radios, the truth is that in many cases you would not be able to distinguish these radios on the air from an “actual” certified 10 meter radio such as the HTX-100 or HTX-10. While the addition of echo and talkback reminds us that the target audience for these radios may not be the U.S. amateur community, I don’t want to discredit their actual ability to be used as 10 meter radios. The key to running a Magnum 257 HP on ham frequencies is to run the radio at moderate levels of modulation and to follow all rules and regulations appropriately.


One of the things I always promote is for people to do their own tuning and modifications. (Give a man a fish and you feed him for a day. Teach a man to fish and you feed him for a lifetime.)

With the Magnum 257 HP I think most people can easily attempt the frequency conversion and adjusting the microphone gain on the potentiometer located inside the microphone is fairly straightforward, but for this radio that’s where I’ll tell you to stop.

Truthfully there isn’t really much need to go inside this radio. Straight from the factory it was doing great numbers and the audio was excellent. I actually ended up turning down the pot inside the microphone as I felt the audio was even a little loud for SSB. Because this radio uses the Top Gun Compressor you won’t find any huge changes in audio from playing around with the modulation pot. This radio has variable power in AM and SSB modes so no reason to mess with the ALC or AM power pots. If you try to run the deadkey higher than the recommended 15 watts you’re likely to damage the RFX 75.

Adding to my reasons for the average Joe not to poke around inside is that the components of this radio aren’t labeled. There isn’t a whole lot of info online on what parts are located where and so it could be hard to figure out for many people which might be a good thing. I think many techs out there could do more harm than good by messing around with this radio. The Magnum 257 HP uses surface mount components and many techs don’t have the skill necessary for doing work on these radios (not that you should need to mess with any of the SMT components anyway). The board is high quality and SMT technology usually mean better durability so I think these radios shouldn’t require much in the way of repairs or modifications to the board.

If you have a good local tech you could have him quiet down the receive just a bit if you prefer, but for the most part I’d just run this radio and enjoy.


If you read my original Magnum 257 review you already knew I liked this radio. I was a big fan of the Uniden PC122XL back in the day and the Magnum 257 HP is twice the radio in the same small package.

Now while you can read reviews talking about all the technical aspects of a radio I think I can sum up why I like these radios so much.

For my very first test with this radio I ran it into a the small K30 magnet mount antenna on my wife’s car and during that test I started hearing some DX rolling in. I gave a call and sure enough I had a solid contact with a station in Arizona. He gave me a big thumbs up on the sound of the radio and the 60-70 watts output of the Magnum 257 HP was plenty enough to make additional contacts throughout the evening commute.

The second night of testing I ran the radio in my mobile and made multiple DX contacts within minutes.

Now there are many factors that could have been at play (DX conditions being better than normal, etc) but my general impression was that with the Magnum 257 HP it was just plain easy to get my numbers called out there in DX land. I had multiple stations telling me that the radio sounded great and I got very good signal reports. Once again, this may not mean much since it’s just my personal “feel”, but when you’ve owned as many radios as I have, if something seems to work easily for DX you usually can tell.

Now out of the conjecture and into some straight talk.

The Magnum 257 HP is a very compact AM, FM, SSB export radio. The addition of the RFX 75 makes it more powerful than just about all the standard dual final exports available on the market. It’s known as one of the best SSB radios available and the addition of the Top Gun Compressor means that these newer models sound much better on AM than the original amber display models.

Complaints from people about this radio usually focus less on its ability or performance and more on its design. The knobs can be small for those with big hands, the labels on the buttons and below the knobs can be difficult to read, and because it’s so compact it’s possible to bump knobs accidentally.

While operating a small radio with small knobs might be slightly more difficult, the modern styling and small size make this radio a great match for newer vehicles. I can’t tell you how many people over the years have told me that they wished there were more modern looking CB’s to run in their new cars. I can’t blame them, most people don’t want a shiny chrome radio in their new Honda with black plastic interior. The Magnum 257 HP with it’s blue lights is the perfect compliment to a newer vehicle.

So in closing, the Magnum 257 HP has been a favorite for years and this new version takes that same radio and gives it a steroid boost. If you liked the Magnum 257 previously you’re going to like the new HP version. If you’re one of the people who complained about the small knobs and “hot receiver” on the old models than you probably will complain about the same things on the new version. Overall though this is a powerful radio in a small package and that is a fact. 73’s.


Top Gun Compressor (black rectangle with orange and yellow wires)