Icom M700 Mods -

The M700 puts out a raw 150W PEP. Running this into a modern 100W-rated antenna tuner can melt toroids. The fix: Adjust the ALC (Automatic Level Control) threshold.

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

The M700 relies on convection cooling. For contesting or FT8 (high duty cycle), it gets scorching hot.

In an era of SDRs and $1000 Chinese "all-band, all-mode" rigs, the Icom IC-M700 seems anachronistic. But a fully modified M700 offers something no new radio can: 150 watts of commercial-grade RF output, a front end that won't blow out in a contest, and a level of reliability that has earned it the nickname "The Brick."

With these modifications, you transform a limited-purpose marine radio into a genuine HF contesting, DXing, and emergency communications asset. The M700 will never have a spectrum scope, but it will be working long after cheaper rigs have died.

Final Warning: Many of these modifications (especially the MARS/CAP unlock) are unlawful to use on the amateur bands if your radio lacks Part 97 certification? Actually, hams can modify equipment – but you must never transmit outside the amateur bands with this radio. Use the MARS mod only to gain access to legal ham frequencies.

Now fire up the soldering iron, download the IC-M700 service manual (available freely on Mods.dk), and give this marine dinosaur a new life on the air. 73.

The Icom IC-M700, originally a 150-watt marine HF SSB radiotelephone from the 1980s

, has become a popular project for amateur radio enthusiasts due to its robust build and low cost on the second-hand market. While powerful, its original firmware and hardware are strictly tailored for marine use, necessitating several modifications to make it a versatile amateur station. Frequency Expansion and Control

The most fundamental modification is enabling the radio to transmit outside of its factory-set marine bands (MARS/CAP and Amateur Radio expansion). Transmit Enable Jumper

: Transmit on all covered frequencies (1.6 to 23.999 MHz) can be enabled by ensuring W37 (W1037) on the Logic Board is installed/soldered. Memory Lockout

: To allow programming for Banks A and B, which are often locked, W33 (W1033) should be removed. VCO Retuning

: Coverage can be extended into the 10-meter and 11-meter bands (above 24 MHz) by editing the internal SRAM contents and manually retuning the VCO. Keyboard Restoration

: If the 10-key numeric buttons are non-functional, toggling switch on the Matrix board can often restore them. Memory and Logic Upgrades

The IC-M700's native 48-channel limit is a significant bottleneck for modern amateur use. SRAM Expansion

: Advanced hobbyists have developed boards to expand memory from 48 to 480 channels icom m700 mods

. This involves modifying the RAM board that stores channel data; since the CPU constantly reads from this SRAM during power-on, external microcontrollers or larger SRAM chips can be interfaced to cycle through multiple memory banks. Split Mode Modification

: For faster channel programming, users have added toggle switches to disable the default "SPLIT" behavior, which otherwise requires separate TX/RX frequency entry even for simplex operation. Audio and Interface Enhancements

Marine radios are optimized for voice punch rather than high-fidelity or digital mode compatibility. Old HF Marine radio for Ham Radio: IC-M700 : r/HamRadio

The DSC upgrade requires a hardware modification and may require professional assistance. Consult an authorized Icom dealer or a qualified technician for this mod.

Safety Precautions and Warranties

When performing mods, be aware of the following:

Conclusion

(and its successor, the M700PRO) is a legendary marine HF transceiver prized by mariners and amateur radio operators alike for its rugged construction and 150W output. While originally designed for marine SSB channels, a few key modifications can transform this workhorse into a versatile HF rig for the ham bands or specialized data use. 1. Transmit Frequency Expansion (MARS/CAP Mod) The most common modification for the

is "opening up" the transmitter. In its stock configuration, the radio often limits transmission to marine bands.

The Jumper Fix: To enable transmit on all covered frequencies (approximately 1.6 MHz to 23.999 MHz), check the Logic Board for jumper W37 (W1037).

If the jumper is cut or missing, the radio may be locked to marine channels.

Action: Solder the jumper (or a wire bridge) back together to unlock general frequency transmission.

Limitations: While this mod covers most HF bands, reaching the 10-meter band (28 MHz) typically requires more complex hardware modifications beyond a simple jumper. 2. Memory and Programming Unlocks

Some regional versions of the M700 have locked memory banks (A and B) to prevent users from accidentally overwriting critical marine frequencies.

W33 Jumper: To allow full front-panel programming of banks A and B, ensure that jumper W33 (W1033) on the Logic Board is NOT installed. The M700 puts out a raw 150W PEP

Keypad Issues: If your 10-key keypad isn't responding, look for switch S1228 on the Matrix board. Toggling this switch can often restore keypad functionality for field programming. 3. Digital Modes and Pactor Integration

Modern operators often want to use the M700 for FT8, Winlink, or Pactor. Because the M700 lacks a modern "Data" port, custom cabling is required.

Audio Interfacing: Modifications often involve tapping into the internal PTT (Push-to-Talk), Line In, and Line Out lines to create a DIN plug interface for a PC or Pactor modem.

Microphone Upgrades: Newer modifications include adapting the 8-pin connector to accept high-quality dynamic microphones or XLR inputs, which can significantly improve audio punch in difficult conditions. 4. Mode and Power Adjustments

AM Emulation: The M700’s AM mode (A3H) actually operates as upper sideband with a carrier. It provides a robust, "loud" signal that is well-suited for broadcasting on non-marine frequencies.

Power Output: While rated at 150W PEP, internal adjustments (usually found in the service manual) can fine-tune the ALC (Automatic Level Control) to ensure you aren't overdriving the final amplifiers during data operation. Comparison: IC-M700PRO ICOM--IC-M700-user-manual.pdf - QRZCQ

Page 3. SECTION 1 SPECIFICATIONS. GENERAL. Frequency Coverage: Receive. Transmit. 1.6MHz ~23.9999MHz. 2.0MHz - 2.9999MHz. 4.0MHz ~ IC-M700 - Single Sideband Radiotelephone - ICOM Canada

The Icom IC-M700 is a legendary marine HF transceiver prized by radio amateurs for its rugged 150W PA and reliable performance. While built for the high seas, several modifications can transform it into a capable "shack" radio for ham operations. Essential Frequency & Transmit Mods

The most common goal for IC-M700 owners is to unlock the radio for amateur band usage.

MARS/CAP Expansion: To enable transmit across the entire covered range (roughly 1.6 MHz to 23 MHz), ensure jumper W37 (W1037) on the Logic Board is installed.

Programming Unlocking: If memory banks A and B are locked out from user programming, remove jumper W33 (W1033) on the Logic Board.

10-Meter Extension: Standard jumpers typically limit the radio to ~23 MHz. Reaching the 10-meter band (28 MHz) usually requires more complex modifications to the band-pass filters and oscillators.

Keypad Activation: If the front-panel 10-key buttons are unresponsive, check the small toggle switch S1228 on the Matrix board to re-enable them. Audio and Interface Enhancements

Improving the M700's transmit audio and connectivity is key for modern ham use.

Microphone Upgrades: The original HM-28 microphone is often replaced with the modern HM-114. Note that this requires replacing the internal connector (53) on the MIC-C-UNIT board. The DSC upgrade requires a hardware modification and

Digital Modes (FT8/SSTV): Enthusiasts often install an external audio interface box. This allows for PC connections via an XLR output for high-quality dynamic mics or direct interfacing for digital modes like FT8.

Speech Processing: Adding an internal speech compressor can significantly boost your signal's "punch" on SSB, which is helpful for maritime mobile nets. Memory and Convenience Hacks

SRAM Expansion: The stock radio has limited channel memory. Some advanced mods use SRAM chips to expand memory up to 480 channels, providing 10x the standard capacity.

Split Mode Toggle: You can install a physical toggle switch to disable "Split Mode," which simplifies and speeds up the programming of simplex frequencies.

Tuning Power Adjust: Internal controls like R19 on the RF board and R247 on the Main board can be used to adjust the tuning power output (standard is 10W) to better match external antenna tuners. Maintenance for Aging Units

Given the IC-M700 was released in the mid-1980s, basic restoration is often the best "mod":

Capacitor Replacement: Replace all electrolytic capacitors, as they are prone to leakage and degradation over time.

Resistor Check: High-wattage carbon resistors (1W and 2W) often drift out of tolerance and should be verified.

PLL Cleaning: If the channel lock is intermittent, cleaning flux residue from the discrete PLL circuit boards can resolve many stability issues.

Are you planning to use the M700 for voice SSB or are you looking to set it up for digital data modes like Winlink? IC-M700 Mods - Elliott Liggett - GitLab

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.

If you want the "perfect" amateur-grade IC-M700, here is your shopping list of modifications: