Icom M700 - Mods

The most common modification requested for the M-700 is the removal of the maritime frequency restrictions.

The Context: Marine radios are type-accepted for specific maritime bands (Tx 1.6–27.5 MHz). They are not legally permitted to transmit on Amateur Radio bands (160m through 10m). However, the hardware inside the M-700 is fully capable of operating across a broad spectrum of HF frequencies.

The Procedure: Unlike modern radios that require complex software hacks or "firmware cracks," the M-700 mods are refreshingly analog. The radio uses a matrix of diodes on the control logic board to define its frequency range and operational modes.

The Deep Risk: While the mod is electrically simple, it comes with risks. The output filtering network on the M-700 is optimized for marine bands. Transmitting on, say, the 80-meter amateur band (3.5 MHz) with an M-700 can result in high SWR (Standing Wave Ratio) internal to the radio, potentially stressing the final transistors (MOSFETs) if an external tuner isn't perfectly matched.

Note: This guide focuses on legitimate, safety-first, and legal modifications for the Icom IC-M700 (marine VHF fixed station) to improve usability, reliability, and integration. Do not perform modifications that violate local radio laws, FCC/ITU regulations, or that alter the unit’s certified transmission characteristics (e.g., increasing transmit power beyond spec, changing frequencies, or bypassing required emission limits). Always consult a certified radio technician or Icom for repairs that impact RF circuits or safety. Use this guide only for permitted hardware, ergonomic, and software/firmware tweaks that do not change certified RF parameters.

Contents

Quick checklist for a safe mod/install

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The Icom IC-M700 is a classic marine HF transceiver that can be modified into a highly capable ham radio rig

. Below is a summary of the most common and effective modifications for this unit. Core Frequency & Programming Mods

These modifications unlock the radio's full potential by allowing it to operate outside restricted marine bands. Transmit Frequency Expansion (MARS/CAP):

To enable transmit on all covered frequencies (approx. 1.6 MHz to 23.9 MHz), check the Logic Board for jumper

). If this wire is cut, solder it back together to restore full range. Enable Memory Programming:

If banks A and B are locked out from programming, ensure jumper ) on the Logic Board is not installed Enable Keypad Entry: If the front-panel 10-key buttons aren't working, check the Matrix board for a small toggle switch, Performance & User Experience Upgrades

Advanced mods can modernize the radio for contemporary amateur use. Memory Expansion: You can upgrade the standard 48 memory channels to 480 channels

by performing an SRAM expansion. Detailed schematics for this ramboard mod are available via community repositories. Audio & Digital Modes: External Audio Interface:

Constructing an interface box allows you to connect the radio to a PC for digital modes like Modern Microphone Adapters: The most common modification requested for the M-700

You can modify the mic socket to accept newer microphones or high-quality dynamic mics with XLR outputs. Speech Processor:

Adding an internal speech compressor can significantly improve your signal punch during SSB operations. Operational Tips for Ham Use

The radio's "AM" mode is actually upper sideband with a 40-watt carrier (A3H), which provides a loud, fully modulated sound compatible with most AM receivers. Split Mode:

Some users install a dedicated toggle switch to disable "split" behavior, making standard simplex programming faster. Filter Limitations:

While the radio works well on amateur bands, it lacks the narrow filtering found in dedicated ham rigs, which may make it sensitive to nearby interference during contests.

For deep technical dives and step-by-step guides, refer to the IC-M700 Mods repository on GitLab or the extensive archive at Do you have a specific version

of the M700 (like the M700TY or PRO) that you're working on? IC-M700 Mods - Elliott Liggett - GitLab

Stock M700 audio is optimized for marine voice—often too bassy for ham radio.

If you want the "perfect" amateur-grade IC-M700, here is your shopping list of modifications: The Deep Risk: While the mod is electrically

The IC-M700 typically uses tube (valve) finals (often 6JS6C or similar sweep tubes). Solid-state versions exist but are less common.

Maintenance/Modification:

The IC-M700 is a pure analog radio – no CAT control. But with a simple Arduino or PIC-based interface, you can add frequency readout and control via a computer.

The "HobbyPCB" or "Arduino M700 Mod":

For full CAT control: Use the Arduino to output a control voltage via a DAC (Digital-to-Analog converter) back to the VCO line. You can then tune the M700 from your PC using Ham Radio Deluxe. This is advanced, but the schematics are widely available.

The most sought-after Icom M700 mod is the full frequency unlock. Without this, you are limited to marine channelized operation. With it, you get continuous TX from 1.6 MHz to 30 MHz, covering all amateur bands.

The Icom M700 is a legend. Built like a tank for the harsh marine environment, this 150-watt HF SSB transceiver was a staple on commercial vessels and cruising yachts for decades. While its rugged build and powerful output are still revered, the stock unit is showing its age—especially for amateur radio operators (hams) who acquire surplus units.

However, the digital age and a passionate community of modders have breathed new life into this classic rig. The right Icom M700 mods can transform this marine radio into a modern, versatile, high-performance ham transceiver. This guide explores the most valuable, safe, and effective modifications to boost frequency coverage, audio quality, and usability.

Disclaimer: Modifying electronic equipment requires soldering skills, knowledge of high-voltage circuits (the M700 has lethal voltages inside), and proper test equipment. The author assumes no liability for damage to your radio, your vessel, or your person. Proceed at your own risk.