Kenwood Tkm707 Mods Review
Kenwood TKM-707 is a robust 150-watt marine SSB radiotelephone that has become a popular project for amateur radio operators looking for a high-power, rugged transceiver. While it is a marine-grade device, several modifications can adapt it for wider use. Common Modifications & Internal Settings Technical enthusiasts often look to expand the
's capabilities beyond its factory-set marine channels. Detailed schematics and procedures for these modifications can be found in the archives at mods.dk Frequency Expansion:
The unit is designed to cover marine bands from 2 MHz to 27.8 MHz, with a general coverage receiver from 500 kHz to 30 MHz. Some users seek to enable transmit capabilities across the entire 1.6 MHz to 30 MHz range for amateur radio use. Audio and Tone Adjustments:
The internal maintenance board allows for fine-tuning of the audio experience. Beep Tone Level: You can adjust the potentiometer to change the beep volume. Alarm Tone Level: Adjust the
after entering Alarm Test mode (pressing the ALARM key) to set the desired volume for alerts. VFO Control:
features 198 memory channels (including 150 factory-programmable and 62 user-programmable), advanced users often mod the unit to allow for more flexible VFO (Variable Frequency Oscillator) tuning similar to a standard ham radio Hardware & Connectivity Mods kenwood tkm707 mods
For better performance in non-marine environments, consider these hardware tweaks: Antenna Coupler Integration: The radio is frequently used with the MAT-100 automatic antenna coupler
. For optimal performance, especially on low frequencies, it is recommended to use a wire antenna between 12 and 23 meters long. Microphone Pinouts:
The front-panel microphone connector uses an 8-pin configuration. Modification of the mic circuit is sometimes necessary when adapting standard Kenwood desk mics (like the MC-60) for this marine chassis. Cooling Improvements: Although the
has a large cooling system capable of continuous full-power transmission for over an hour, adding external fans to the rear aluminum chassis is a common mod for digital mode enthusiasts (like FT8) who require heavy duty cycles Essential Technical Resources
For step-by-step disassembly and component-level repair, these manuals are indispensable: Service Manual (Scribd) Kenwood TKM-707 is a robust 150-watt marine SSB
Contains the full circuit descriptions and PLL block diagrams. User Manual & Installation Guide (Scribd)
Useful for understanding the basic function keys and initial setup. Free Service Manual PDF (Elektrotanya) A common repository for direct downloads.
The "proper story" behind the Kenwood TKM-707 modifications is a classic tale of 1990s radio engineering: a high-quality piece of consumer hardware that was secretly a professional-grade transmitter waiting to be unlocked.
Here is the history, the technical reality, and the specific modifications for the Kenwood TKM-707.
Mic Gain & Compression Mod:
The stock microphone gain is anemic, especially with dynamic mics. To boost audio: Open the mic
- Open the mic. Locate the electret element (most TKM-707 mics are electret, not dynamic).
- Increase C8 (mic preamp cap) from 0.47uF to 2.2uF to enhance low-end.
- Add a 1k resistor in parallel with R5 (mic gain feedback) to increase overall gain by ~6dB. Alternatively, use an external outboard preamp like a W2IHY or Behringer.
3. Transmit Audio Improvements
The TKM-707 is famous for having a very hot transmit audio circuit. While this ensures you are heard, it can lead to over-deviation and "muddiness" if you use a high-gain microphone.
The Mic Gain Resistor Mod: If you are using a non-standard microphone (like a D-104 or a modern Heil mic), you may need to adjust the input sensitivity.
- Open the radio and locate the mic preamp section.
- Solder a resistor in parallel or series with the mic input line to attenuate the voltage.
- This prevents "splatter" (bleeding over onto adjacent channels) and keeps your signal clean and narrow.
The "Heil" Upgrade: Many owners choose to bypass the stock electret element entirely. Modifying the mic jack to support a dynamic microphone usually requires adding a bias resistor or removing one, depending on the revision of the mainboard. Dynamic microphones generally offer superior noise rejection compared to the stock Kenwood handheld mic.
Adding an External Noise Blanker Tap:
If you operate mobile or in a high-RF noise environment, you can add a pre-amp bypass or tap the IF output to connect a Timewave DSP-599zx or similar.
- Locate the 1st IF filter (49.275 MHz on most schematics).
- Use a 10pF capacitor to tap the signal before the IF IC.
- Run a shielded coax to a rear-panel BNC added in a blank hole.
- This allows external DSP or an SDR panadapter.
1. TX/RX Coverage Expansion
- TX/RX Coverage Modification: One of the common mods involves expanding the transmit and receive coverage of the TK-M707. The stock radio is set for amateur bands, but users often want to operate on other frequencies, such as the shortwave bands for HF communication. This usually involves component changes and alignments to shift the coverage.
Part 1: The Essential Mod – Frequency Expansion (MARS/CAP)
The most common search leading to “kenwood tkm707 mods” is the need to open the TX/RX frequency range. By default, the TKM-707 transmits only on ITU marine channels. For amateur bands (160m, 80m, 40m, 30m, 20m, 17m, 15m, 12m, 10m) and MARS/CAP frequencies, you need to perform a simple diode mod.
Part 2: Power Output Adjustments – Getting Clean Watts
The TKM-707 is rated for 150W PEP. However, many units drift with age, and the final transistors (2SC2879) can be pushed further – but do so at your own risk. The most useful mod here is reducing power for digital modes and setting a stable 100W carrier.