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RE: sidebands of CW signals



One possibility was brought up as part of a PSK-31 discussion.  Some radios generate their CW signal by keying an audio tone on and off, and using the SSB audio chain to drive the balanced modulator.  If the audio tone is low enough, and distorted enough, its harmonics would fall within the passband (after modulation) of the SSB transmit crystal filter.  And those TNC's or soundcards for their generation of CW would be even more likely to suffer these problems.  The solution suggested for PSK-31 operations was to make sure your transmitted audio tone is 1500 Hz or above - so the second harmonic is above the edge of the SSB filter.  This is also why some manufacturers of RTTY/AMTOR/etc. used tones above 2 kHz for their AFSK-based products - to take advantage of the filter skirts in the radio to prevent audio harmonics from making it on to the air.

73, Bob, KD7NM

>-----Original Message-----
>From: Wayne Estes W9AE [mailto:w9ae@earthlink.net]
>Sent: Wednesday, July 30, 2003 2:35 AM
>To: amsat-bb@AMSAT.Org
>Subject: [amsat-bb] sidebands of CW signals
>
>
>I often hear weak sidebands of strong CW signals on AO40.  The 
>sidebands are
>2-3 kHz away from the strong signal.
>
>Would that be a sideband transmitted by the CW station, or is it a
>distortion product of the transponder?
>
>Wayne Estes W9AE
>Mundelein, IL, USA
>
>
>----
>Sent via amsat-bb@amsat.org. Opinions expressed are those of 
>the author.
>Not an AMSAT member? Join now to support the amateur satellite program!
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>

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