You might try this instead. Used them successfully on my early (1978) Goldwing for several years.
Jeff,
Thanks for your input. I have looked at this area but you really need good gel headphones to hear the scanner at the track. The portable aviation intercom allows us to talk back and forth (we are sitting or standing next to each other) with good quiet headphones and voice activated mikes, they're just not plugged into a radio. Most are a very small package with volume, squelch and a separate audio input for stereo, etc. A scanner's headphone output plugs into this input easily. Works great loud and clear without any hassles other than wrapping up the extra headphone and mike output cable.
