I don't like handheld microphones. Headphones with a microphone give me the advantage of having both hands free, some isolation from ambient noise, and a constant distance between the microphone and my mouth. An electret microphone has a flat frequency response, high output voltage, compact size, and a low price. These days, it’s no problem to buy a desktop microphone or a headset with a microphone for your computer for just a few euros. But how do you connect them to a transceiver?
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Tip: The Effect of the Decoupling Capacitor
Many amateur radio operators have ruined their connections by choosing the wrong decoupling capacitor. The input impedance of the transceiver’s microphone input is 600 ohms. If the value of the decoupling capacitor is too low, a frequency-dependent voltage divider is created. Low frequencies picked up by the microphone are attenuated. This is incorrect.
Every voice has its own unique characteristics. Attenuating low frequencies can thus result in a significant change in tone. Furthermore, most transceivers have a built-in filter for very low frequencies, which we do not need for communication. At the same time, they have an equalizer or adjustable frequency response.
Therefore, I feed the signal from the microphone without significant modification and use the settings to adjust the frequency response of the transmitted signal so that it best suits my needs.
Electret Microphone for the Kenwood TS-2000
The advantage is that the microphone connector on the Kenwood TS-2000 provides an 8V supply voltage (max. 10mA). The electret microphone is powered from this source via a resistor, and the modulation voltage is fed into the transceiver via a decoupling capacitor. The value of the coupling capacitor is 2.2 uF. The -3 dB cutoff frequency is therefore 120 Hz.
Schematic diagram of the interface for an electret microphone for the Kenwood TS-2000 transceiver
The entire circuit is so small that it can easily be built directly into the microphone connector. A short cable terminated with a CINCH connector for the PTT footswitch is also routed from it.
Modulation Settings for the Kenwood TS-2000
The TS-2000 allows you to set the bandwidth of the transmitted signal in menu #22. Bandwidths ranging from 2.0 to 3.0 kHz are available. However, they also differ in their lower and upper frequencies. I prefer the 2.6 kHz bandwidth. The narrower bandwidth has a lower frequency of 300 Hz, which audibly alters the character of my voice.
Menu No. 21 contains the TX equalizer. I have it set to H, which emphasizes the treble.
I set the microphone signal level according to the ALC (I use a value of 30). I have the speech processor level set to 35. This signal also meets the criteria listed at https://cq.sk/zly-a-horsi-ssb-signal/. However, your settings may differ.
