K9STH
01-29-2002, 12:30 AM
Primarily because there is very little of the circuitry that would be common between the two modes. Possibly the audio portions of both the transmitter and receiver, and the receiver "front end". Otherwise, an FM transmitter is basically class "C" operation and can use frequency multiplication if necessary. Even if it is heterodyne type of circuitry, for best efficiency the final amplifier runs class "C". For SSB you would need much closer "steps" in frequency (i.e. 10 Hz instead of 5 KHz like on most FM units), and a final amplifier that runs Class A, B, AB-1, or AB-2. The receiver would have to be independently tunable from the transmitter since any difference of over 50 to 100 Hz makes the received SSB signal greatly distorted. Of course, the receiver can control the transmit frequency and that must have the closer steps in frequency.
In addition, the frequency stability of an SSB signal must be several magnitudes better than that of an FM signal.
It is possible to build a portable that runs FM, AM, CW, and SSB. But, it would be more expensive and would probably be a fair bit larger than what you are used to.
Glen, K9STH
Contact: gzook@attbi.com
In addition, the frequency stability of an SSB signal must be several magnitudes better than that of an FM signal.
It is possible to build a portable that runs FM, AM, CW, and SSB. But, it would be more expensive and would probably be a fair bit larger than what you are used to.
Glen, K9STH
Contact: gzook@attbi.com