Kenwood Tkm-707 Mods Direct

| Modification | Improvement | Difficulty | |--------------|-------------|-------------| | Re-capping PSU board | Reduce ripple/noise | Medium | | Adjusting TX bias (VR1, VR2 on RF unit) | Better IMD | High (requires service monitor) | | Adding heatsink fan (12V triggered by TX) | Reduced PA temperature | Low |

The radio has a sharp Collins mechanical filter (often 2.4 kHz for SSB). For AM broadcast listening or DRM, this is too narrow.

The TKM-707 is a marine radio. Marine HF uses Upper Sideband exclusively (except for some inter-ship on 2 MHz, which sometimes uses J3E - similar). Amateur radio uses LSB on 160, 80, and 40 meters. Without LSB, you can only listen to half the conversations.

The radio generates its carrier frequency based on a 9 MHz IF (Intermediate Frequency). To switch from USB (+1.5 kHz offset) to LSB (-1.5 kHz offset), you need to alter the BFO (Beat Frequency Oscillator) injection. Kenwood Tkm-707 Mods

Hardware Method (Adding a switch):

  • Wire the switch to select between the grounds of the two crystals.

    • Software/Service Menu Method (Some firmware versions):

    Result: A flip of a switch gives you full LSB capability on 75m and 40m rag-chews. Wire the switch to select between the grounds

    Out of the box, the TKM-707 is often locked to specific commercial frequencies. For the amateur radio operator, the most critical modification is opening up the transmit and receive range to cover the entire 2-meter band (144–148 MHz).

    This is almost exclusively a software modification. Unlike older radios that required cutting traces or soldering diodes, the TKM-707 is programmed via a cable connected to a PC.

    This is less of a hardware mod and more of a programming exploit using the front panel. Software/Service Menu Method (Some firmware versions):

    Steps to enable "Screwdriver" VFO mode:

    Result: The tuning dial now behaves like a true VFO. You can tune from 1.600.00 to 29.999.99 MHz in continuous 10 Hz steps. This is essential for chasing SSB nets or tuning in digital modes like FT8.

    The TKM-707’s clarifier is great for fine-tuning marine nets, but it lacks the range for SSB phone rag-chewing where operators might drift.

    The Fix: Locate the trimmer capacitor (TC1) on the PLL board. By tweaking this or replacing a fixed resistor in the clarifier circuit (R158), you can expand the adjustment range from ±50Hz to ±200Hz.

    Why you need it: This turns the clarifier from a "fine tune" into a proper "voice finder." No more asking the other station to re-tune their Drake.