The M700 uses a Phase-Locked Loop (PLL) with programmable dividers. Jumpers on the main PLL board (often labeled the "PLL Unit" or "Frequency Unit") set the frequency limits. By changing diode or jumper configurations, you override the marine band limits.
The receiver uses a de-emphasis circuit (a simple RC filter) that kills treble. By changing a few capacitor values, you can get a much flatter, more pleasant audio response.
Specific Steps:
The "Audio Tap" Mod: For digital modes, tap the audio before the de-emphasis network (directly from the FM detector IC) and route it to a rear-panel RCA jack. This gives you a clean, flat 300–2700 Hz output for your sound card, vastly improving FT8 decoding performance.
If you want the "perfect" amateur-grade IC-M700, here is your shopping list of modifications: icom m700 mods
| Mod | Difficulty | Time | Benefit | | :--- | :--- | :--- | :--- | | MARS/CAP Unlock | Medium (Soldering) | 30 min | Transmit on all HF amateur bands | | Audio Coupling (C37/C133) | Easy | 15 min | Warm, clear receive audio | | Mic Bias & EQ | Medium | 20 min | Use modern condenser mics | | ALC Threshold (R28) | Medium | 30 min | Cleaner SSB output | | Noise Blanker Threshold | Advanced | 1 hour | Usable impulse noise reduction | | Arduino Digital Readout | Advanced | 2-3 hours | Digital VFO function | | Fan Thermostat Mod | Easy | 15 min | Improved thermal management |
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 M700 uses a Phase-Locked Loop (PLL) with
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. The "Audio Tap" Mod: For digital modes, tap