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Title: Compatible SSB = AM Post by: NE4AM on February 02, 2006, 03:33:06 PM IN THE EVENT that RM-11306 passes, all is not lost! There is a technology that will allow savvy hams to continue using our beloved AM. This is Compatible Single-Sideband (CSSB). The basic concept is that the carrier of a conventional AM transmitter is phase modulated in such a way that when the phase-modulated carrier is amplitude modulation, the PM bessel sidebands are canceled by the AM sidebands, while being capable of being received by a conventional envelope detector. Leonard Kahn was a pioneer in this technology, and holds a couple patents:
US3218393 Nov., 1965 Kahn US3908090 Sep., 1975 Kahn He currently markets a system called 'Powerside' which allows a broadcast transmitter to transmit CSSB. A Class-E Tx with PWM modulation is the ideal platform for CSSB. Any takers? 73 - Dave NE4AM Title: Re: Compatible SSB = AM Post by: W1DAN on February 02, 2006, 04:08:17 PM Hi Dave:
Great idea! I they make AM illegal, we can use CSSB! I wanna do AM stereo! I think WA1SOV has doen it already. 73 Dan W1DAN Title: Re: Compatible SSB = AM Post by: Steve - WB3HUZ on February 12, 2006, 12:10:35 PM WA2FNQ has run stereo too. Here's a recording.
http://www.amwindow.org/audio/htm/wa2fnq.htm Title: Re: Compatible SSB = AM Post by: Gary - WA4IAM on February 12, 2006, 05:22:46 PM Wow! Pretty impressive recording. Too bad I don't have anything that will decode the on air signal here in the shack. That would be cool! 8)
Title: Re: Compatible SSB = AM Post by: k4kyv on February 12, 2006, 11:59:02 PM CSSB does not affect the total bandwidth of the signal. It folds the spectrum of the signal in such a way as to shift all the sideband energy to one side of the carrier, but introduces higher order sideband components that make the one sideband double the normal bandwidthl. It is useful where two stations cause strong adjacent channel interference to each other. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
If, for example, it is desired to avoid interfering with the adjacent channel on the lower side of the carrier, the CSSB signal would place all the sideband information on the upper side of the carrier. As a simplified example, if the signal is modulated 100% with a single tone, the carrier power shifts downwards, while the upper sideband amplitude has double the amplitude of the reduced carrier. Then there is a 2nd order upper sideband, a product of the phase modulated component, spaced equally above the 1st order usb, equal in amplitude to the suppressed carrier. The phasing of the carrier and sideband components is such that the signal appears to the envelope detector exactly as if the 1st order upper sideband were the carrier, and the actual carrier and 2nd order sideband were usb and lsb. Of course, the picture gets more complicated with the complex modulating waveforms of voice and music. CSSB is not the same thing as the bogus "AM" mode of some ham SSB rigs such as the Drake TR-7 and Collins KWS-1, which generate full carrier and just one normal sideband. You don't get something for nothing. |