M700 Mods - Icom

A common complaint among audiophiles and DXers (long-distance listeners) regarding the M-700 is the audio filtering.

The "Filter Swap": The stock ceramic filters in the IF (Intermediate Frequency) stages are chosen for durability and "communications grade" audio—essentially, intelligibility over fidelity. They are often slightly too narrow, resulting in a "pinched" or tinny sound.

The IC-M700's stock audio is optimized for voice intelligibility in a noisy engine room on a fishing trawler. It's punchy but lacks low-end "warmth." For amateur SSB operation, where you want a fuller, less fatiguing sound, the audio coupling capacitor mod is essential.

The Problem: The audio path uses small-value capacitors that roll off frequencies below 300 Hz. This kills bass response, making your receive audio sound "tinny."

The Solution: Increase the value of two specific capacitors on the Audio (AF) unit.

Why this works: These capacitors form high-pass filters in the receive audio chain. By increasing their capacitance, you lower the cutoff frequency to approximately 80-100 Hz, allowing natural voice fundamentals and low-end richness to pass through.

Bonus Audio Mod: The M700's microphone preamp is designed for dynamic marine microphones. If you are using a modern electret condenser mic (like a Heil headset), you need to add a 5-10 µF capacitor in series with the mic line (pin 1 of the mic connector) and also install a 2.2k ohm resistor to provide bias voltage. This will boost your transmitted audio to "broadcast quality."

No deep piece on the M-700 mods is complete without mentioning the AT-130 automatic antenna tuner.

The M-700 is almost always paired with an Icom AT-130 or AT-140. While not a modification to the radio chassis itself, the "mod" here is often in the installation.

Modifying the Icom IC-M700 (and the newer M700PRO) is a common practice among amateur radio enthusiasts who want to adapt this robust marine SSB transceiver for ham radio use. Because it was originally designed for the marine environment, it lacks several standard "ham" features like a VFO dial and certain operating modes, which these modifications aim to restore. Core Ham Radio Modifications

The primary goal for ham operators is to unlock the radio's frequency flexibility and improve its interface for non-marine use.

Frequency Expansion (Out-of-Band Transmit): By default, the M700 is often locked to specific marine channels. Modifications can enable "wide-band" transmit, allowing the radio to operate on amateur HF bands.

VFO Implementation: One of the biggest hurdles is the lack of a continuous tuning dial (VFO). Enthusiasts have developed custom hardware projects, sometimes using microcontrollers like Arduino, to interface with the radio's internal PLL and provide a digital VFO display and tuning knob.

LSB/USB Mode Switching: Most marine HF communication is USB only. For lower ham bands (like 40m or 80m), LSB is the standard. Mods often involve adding a toggle switch or internal circuitry to flip the sideband. Technical and Connectivity Mods

Beyond frequency control, hardware tweaks can improve the radio's performance or allow it to interface with modern digital equipment. icom m700 mods

Pactor and Digital Mode Interfacing: Since the M700 uses a non-standard microphone connector (often 7 or 8-pin), users frequently build interface boxes. These boxes bridge the radio’s Mic/PTT and Speaker outputs to a Pactor modem or a computer sound card for digital modes like FT8 or JS8Call.

Internal Component Upgrades: Long-term reliability fixes include replacing old electrolytic capacitors or modifying the oscillator power to reduce RF voltage leakage across varactor diodes, which can prevent frequency drift over time.

Power Supply Connectivity: Many M700 units are found without their original 6-pin power plugs. Standard mods include hardwiring power leads or adapting more common high-current connectors to ensure the radio gets the stable DC voltage it needs to hit its 150W peak output. Critical Resources for M700 Mods

If you are performing these mods yourself, these specialized repositories are the standard references:

Mods.dk - IC-M700 Section: The most comprehensive archive for specific hardware jumper settings and legacy repair articles.

Elliott Liggett’s GitLab Repository: A modern resource focusing on making the M700 more user-friendly for ham use, including video demonstrations of active mods.

Manualslib Icom M700 Service Manual: Essential for identifying test points and circuit paths before soldering. ICOM M700 Modification - Google Groups

For detailed technical documentation on modifying the Icom IC-M700

for amateur radio or expanded use, the most comprehensive "paper" available is the Technical Write-up by Elliott Liggett (W6EL) This repository and its associated video guide

detail several critical modifications for converting this marine HF radio into a versatile ham radio. Key Modifications for the IC-M700 Frequency & Memory Expansion All-Band Transmit

: Closing a specific internal jumper typically allows transmit coverage from approximately 1.6 MHz to 23 MHz SRAM Upgrade

: Replacing the standard memory can expand the radio from its original 48 channels to 480 channels 10-Meter Band

: Expanding coverage to include 10/11 meters requires hex editing the SRAM contents (reversing frequency data) and retuning the VCO. Audio & Hardware Upgrades Speech Compressor

: Adding a speech processor to improve transmit audio punch for amateur use. Microphone Replacement : Because the original HM28 microphone is discontinued, a modification procedure exists to adapt the microphone, involving internal board unsoldering. Digital Modes Why this works: These capacitors form high-pass filters

: Modifications to the internal mic connector can facilitate an external audio interface for digital modes like Functional Tweaks Split Mode Disable

: Installing a switch to disable split mode for simplified simplex operation. LSB vs. USB

: The radio supports both, but note that in some modes, the upper sideband features a carrier suppressed by 16 dB below peak power. Essential Reference Documents Service Manual

: Necessary for identifying board layouts and test points. It is available on RadioManual Modifications Compendium

: A large collection of various Icom-specific hacks can be found in the All ICOM Mods from Mods.dk or more detailed step-by-step instructions for the SRAM memory expansion? Old HF Marine radio for Ham Radio: IC-M700 : r/HamRadio

The Icom IC-M700, a legacy marine HF transceiver first sold in 1984, is a popular candidate for modifications to make it suitable for amateur radio use. Because it was originally designed for maritime service, its standard features often lack the flexibility required for ham radio operation. Core Functional Modifications

These mods focus on unlocking the radio's hardware potential for broader frequency use:

MARS/CAP & Frequency Expansion: To enable transmit capabilities across all covered frequencies (roughly 1.6 MHz to 23 MHz), ensure that jumper W37 (W1037) on the logic board is installed; if cut, it must be soldered back together. Expanding coverage to the 10-meter band typically requires further board-level adjustments.

Memory Expansion: The stock radio is limited to 48 channels. Specialized mods, such as an SRAM expansion, can increase this capacity to 480 channels.

Programming Unlocking: To allow programming of memory banks A and B, ensure that jumper W33 (W1033) is not installed. If the 10-keypad is unresponsive, toggle switch S1228 on the Matrix board.

Split Mode Toggle: A common modification involves adding a switch to disable "split mode" behavior, which facilitates faster channel programming for amateur use. Audio & Performance Upgrades

Microphone & Speech Processing: Users often modify the microphone gain or add a speech compressor to improve signal punch on SSB. Modern replacements like the HM-180 8-pin microphone are frequently used to replace aging EM-101 models.

External Reference Injection: For those requiring high frequency stability (e.g., for digital modes), boards like the Leo Bodner reference injection board can sometimes be adapted to override the internal oscillator with an external source.

RFI & Noise Reduction: External kits, such as the Palomar Engineers RFI Kit, use ferrite chokes on the DC power and antenna lines to reduce the noise floor and suppress interference. Reference Resources Modifying the Icom IC-M700 (and the newer M700PRO)

For detailed schematics and step-by-step instructions, these repositories and sites are frequently cited by the community:

Elliott Liggett's GitLab: Contains a technical write-up and SRAM schematic for the memory expansion and jumper mods.

Mods.dk: Hosts a collection of over 100 Icom modification documents, including specific guides for the M700's power and lock-out settings. Go to product viewer dialog for this item.

HM-180 8Pin Microphone Speaker Mic for ICOM IC-M700 IC-M710 IC-M600 Radio | Made in China | Clip

Description: NEW HM-180 replace old model EM-101 Hand Microphone For IC-M700 IC-M710 IC-M700PRO IC-M600 (equal EM-48 or HS-50 mic, Go to product viewer dialog for this item.

Hm-180 8pin Microphone Speaker Mic For Icom Ic-m700 Ic-m710 Ic-m600

Description: NEW HM-180 replace old model EM-101 Hand Microphone For IC-M700 IC-M710 IC-M700PRO IC-M600 (equal EM-48 or HS-50 mic, Let's MOD the Icom IC-9700 for Big Jim!

ICOM M-700 Modification Report

The Icom IC-M700 (and its variant the IC-M700TY) is a legacy HF marine transceiver. While robust, it is an older analog radio. Most modifications performed today fall into two categories: restoration (bringing the radio back to spec) and expansion (enabling HAM band usage or replacing obsolete components).

⚠️ WARNING:

The stock M-700 is designed for voice communication—specifically USB (Upper Sideband) for long-range marine traffic and DSC (Digital Selective Calling) for distress.

However, the rise of digital modes (FT8, Pactor, Winlink) and the needs of cruisers necessitated a change.

The "Data" Mod: Operators often open the radio to allow LSB (Lower Sideband) operation. While rarely used for voice at sea, LSB is critical for amateur digital protocols.

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.