Icom M700 Mods _verified_ đź’Ž

Icom IC-M700 is a classic marine HF transceiver that has become a popular project for radio amateurs due to its rugged build and relatively low cost on the used market. To make this commercial-grade radio suitable for hobbyist use, several internal modifications are commonly performed by the amateur community. Core Amateur Radio Modifications

To repurpose the IC-M700 for amateur (ham) radio bands, enthusiasts typically focus on frequency expansion and usability. Frequency Expansion (MARS/CAP):

To enable transmission across all covered frequencies rather than just marine bands, check the Logic Board for jumper W37 (W1037)

. If this jumper is cut, soldering it back together typically opens the transmitter for full frequency coverage. Memory Expansion: The stock M700 is limited to 48 channels. Specialized SRAM expansion mods

can increase this capacity to 480 channels, making it more practical for the various ham bands. Unlocking Programming:

If banks A and B are locked out from programming, ensure jumper W33 (W1033) on the Logic Board is not installed Keypad Activation:

If the 10-key numeric buttons are unresponsive, there is often a small toggle switch, , on the Matrix board that can be used to reactivate them. Audio and Interface Upgrades

Because the original design lacks some fine-tuning features required for amateur use, external and internal audio mods are frequent. Microphone Adjustments:

The standard M700 does not have an external mic gain control. Voltage Jumper: The radio originally supplies

to the microphone connector to power its stock transistorized amplifier. If using a standard dynamic mic or one with its own battery, this internal 8V source should be disconnected via a jumper on the Speech Processing:

Adding an internal speech compressor can significantly improve audio punch during poor band conditions. Pactor Modem Interfacing:

Many users modify the radio to work with Pactor modems for data services like Sailmail. This often involves installing a dedicated lead with a DIN plug that intercepts PTT, Line In, and Line Out signals inside the unit. Performance & Usability Improvements Split Mode Toggle:

Installing a dedicated switch to toggle the "split behavior" can streamline frequency programming. External Feet:

While the unit includes a mobile mounting bracket, it lacks tabletop feet. The bottom of the chassis is already drilled and tapped, making it easy to install standard rubber or plastic feet for desk use. Important Legal Note:

Modifying a marine radio to operate on amateur bands generally voids its type approval for marine use. While legal for licensed hams to use modified equipment on amateur frequencies, it may become illegal to use that same modified unit back on marine channels. or specific pinout diagrams for the microphone connector? IC-M700 Mods - Elliott Liggett - GitLab

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 icom m700 mods

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

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 IC-M700 is a classic marine HF transceiver

CTCSS Modification

  1. Enter the service menu by pressing and holding the [FUNC] and [CLR] buttons while turning on the power.
  2. Navigate to the "SQL TYPE" setting and select "CTCSS".
  3. Set the desired CTCSS tone using the [UP] and [DOWN] buttons.
  4. Save the setting and exit the service menu.

B. Add a 500 Hz CW Filter (M700PRO)

The M700 has no built-in narrow CW filter, making weak-signal work difficult.

  • Mod: Install a 500 Hz Collins mechanical filter (e.g., 526-0233-010) into the FL1 position.
  • Note: You may need to build a small adapter PCB (readily available from third-party hobbyists).

Where to Find More Info

  • Mods.dk – Search “ICOM M700” for user-submitted mods.
  • Groups.io / ICOM-M700 – Active community with detailed PDFs.
  • YouTube – Search “ICOM M700 mars mod” for step-by-step video guides.

Have a unique M700 mod? Share your experience in the comments below!

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:

  1. Licensing: Transmitting on marine frequencies requires a valid Ship Station License. Transmitting on non-marine frequencies (e.g., HAM bands) with a marine radio is illegal in many jurisdictions unless the operator holds an Amateur Radio license and the radio is type-accepted for that service (which the M700 generally is not for HAM use).
  2. Voltage: The M700 is often a 13.8V DC radio. Some variants require 110/220V AC. Verify power input before connecting.
  3. High Voltage: Inside the radio, there are lethal high voltages at the final amplifier tubes even after the power is turned off.

Part 3: The Nasty Noise Blanker (NB) Improvement

The IC-M700 has a rudimentary noise blanker that works poorly on most impulse noise (ignition, power lines). It effectively mutes the receiver rather than clipping the noise pulses.

The Modification: This mod requires adding a modern, standalone noise blanker between the IF output and the audio amp (a "Tiny Noise Blanker" board from eBay or a homebrew design). However, a simpler "soft-mod" exists:

On the MAIN unit, locate R268 (a 1k ohm resistor) associated with the noise blanker switching transistor. Replace it with a 10k ohm potentiometer wired as a variable resistor. This allows you to adjust the threshold of the blanker, turning it from an on/off mute into a usable noise reducer. Dial in just enough blanking to kill the pops without squashing weak signals.

Step-by-Step Guide (Common Method for early M700 models)

  1. Power Down & Unplug. Remove the top and bottom covers.
  2. Locate the PLL Board. This is usually a vertical board near the rear panel, often labeled "PLL UNIT (IC-751 style)" – the M700 shares DNA with the Icom 751 amateur radio.
  3. Identify Jumper Diodes. Look for a matrix of small diodes labeled D1, D2, D3, etc., or a set of solder pads (jumpers). Note: There are several M700 versions (M700, M700TY, M700Pro). The M700TY is the most common and easiest to mod.
  4. The "All Band" Configuration:
    • For the M700TY: Remove diode D13. Add a jumper at JP1 (on some board revisions). Or, set the binary code on the PLL to all F's. The classic mod is to remove D11 and D13, add D12.
    • Pro tip: Search for "Icom M700TY PLL jumper chart" – it varies by serial number range.
  5. Reassemble & Test. After the mod, hold the LOCK button while powering on to enable expanded coverage. You should now be able to VFO tune across all HF bands.

Expected Result: Transmission and reception from 1.600 MHz to 29.999 MHz continuously.

The Verdict: Is the Icom M700 Worth Modding in 2025?

Absolutely—with caveats.

The Icom M700 is not a SDR (Software Defined Radio). It won't give you a waterfall display or a narrow roofing filter. But for the price (often $150–250 at swap meets), you get a 150W transceiver with a receiver front end that rivals radios costing ten times as much.

The icom m700 mods detailed above—especially the PLL unlock and the audio tap—turn a clunky marine brick into a serious contesting, DX, and digital mode machine. It's heavy, it's loud, and it's nearly indestructible.

If you enjoy the smell of rosin flux and the satisfaction of pulling a weak signal out of the noise using a rig you hot-rodded yourself, buy an M700. Open it up. Perform these mods. And join the nets with a piece of radio history that now performs like a modern classic.

Have you performed a unique Icom M700 mod? Share your experience in the comments below.

References: Mods.dk, Icom M700 Service Manual (ICOM Inc.), Repeater-Builder.com M700 forum posts, YouTube user "M0UKD" M700 restoration series. CTCSS Modification

Modifications for the Icom IC-M700 marine HF transceiver focus on expanding transmit frequencies, increasing memory capacity, and enhancing digital mode capability. Key hardware changes include installing jumper W37 for MARS/CAP access and removing jumper W33 for expanded channel programming. For a detailed list of modifications and schematics, visit IC-M700 Mods on GitLab. IC-M700 Mods - Elliott Liggett - GitLab

The Icom IC-M700 Go to product viewer dialog for this item. is a classic marine SSB transceiver that has found a second life among amateur radio operators due to its rugged build and relatively low cost on the used market. While originally restricted to marine frequencies, several hardware and software modifications can unlock its full potential for ham radio and general coverage use. Core Performance Modifications

General Coverage Transmit (MARS/CAP Mod): To enable transmission across all frequencies covered by the radio, verify the state of jumper W37 (W1037) on the Logic Board.

If it is cut, soldering it back together enables wide-band transmit.

Conversely, some regional versions may require cutting this jumper to open the frequency range.

Memory and Programming Unlock: To allow programming of memory banks A and B (which are often factory-locked), ensure jumper W33 (W1033) is not installed.

Frequency Stability Upgrades: For high-precision digital modes, some users install an external reference injection board, such as the Leo Bodner board, to override the internal oscillator and lock the radio to a more stable source. Connectivity and Audio Enhancements Digital Mode Interface (Pactor/FT8): The

can be adapted for digital modes like Pactor or FT8 by tapping into internal signals for PTT, Line In, and Line Out.

A common mod involves adding a DIN plug lead emerging from the back of the radio to interface directly with a Pactor modem or PC sound card.

Microphone Compatibility: Users have successfully modified the internal MIC-Board to eliminate the 8VDC bias, allowing for the use of higher-quality dynamic microphones or modern Icom desk mics like the SM-8.

SRAM Expansion: Technical hobbyists have developed custom SRAM replacement boards that expand the memory from the standard 48 channels up to 480 channels. Operational Hardware Adjustments

10-Keypad Activation: If the front-panel 10-keypad is non-responsive for manual frequency entry, check the small toggle switch S1228 located on the Matrix board.

RFI and Noise Reduction: To improve receiver performance in noisy marine or home environments, specialized RFI filter kits from suppliers like Palomar Engineers can be added to the DC power and antenna lines.

CI-V (Computer Control) Mod – For M700PRO Only

With a simple TTL-to-RS232 adapter, you can control frequency via PC.

  • Mod: Tap into the CI-V bus on the logic unit (usually pin 5 and 6 of IC17). Add a 2.5mm stereo jack.
  • Software: Use ICOM CI-V commands to control with Ham Radio Deluxe.

ICOM M700 Mods: Unlocking the Full Potential of a Classic Marine HF Rig