Path: utzoo!utgpu!ugw.utcs.utoronto.ca!CUVMA!SWL-L Date: Wed, 17 Jan 90 11:35:24 EST Reply-To: Brian Daly Sender: Short Wave Listener's List Comments: Warning -- original Sender: tag was From: Brian Daly Subject: Re: What does one do with an SSB switch? X-To: swl-l@cuvmb.cc.columbia.edu To: UofToronto LAN redistribution Message-ID: <90Jan17.190704est.57639@ugw.utcs.utoronto.ca> Newsgroups: bitnet.swl-l Distribution: ut Approved: devnull@gpu.utcs.toronto.edu Subject: Re: What does one do with an SSB switch? Newsgroups: rec.radio.shortwave Keywords: novice question Summary: Single Sideband mode of operation References: <1265@husc6.harvard.edu> In article <1265@husc6.harvard.edu>, albert@endor.harvard.edu (David Albert) writes: > My Sony 7600DS has an SSB switch, but I have no idea what I might > want to use it for. I'm also not sure what it does (i.e. physically); > is it the equivalent of a narrow-band switch? SSB stands for "single sideband". SSB is a modulation technique which is used quite extensively by amateur radio operators (HAM's), as well as others. In order to understand what SSB modulation is, let's look at amplitude modulation (AM). The purpose of modulation is to put some information onto a radio frequency carrier signal; when you speak into a microphone of a radio transmitter, the electronics within the transmitter "modulates" the RF signal with the voice information. In amplitude modulation, the amplitude of the RF carrier is changed ("modulated") by the message signal (i.e. the voice). If you were to look at the output of an AM transmitter, say with a spectrum analyzer, what you would find is: a carrier signal and two "sidebands". The carrier is the actual RF signal of the transmitter; this carrier contains no information -- you cannot get the voice message back from the carrier signal. The voice message is carried in each of two "sidebands"; these are upper and lower sidebands. Each sideband contains all the message information. This AM signal looks as folows: ^ ^ | ^ | | | ----------------------------------------- LSB Carrier USB where LSB = lower sideband; USB = upper sideband Note that the sidebands are at a slightly different frequency than the carrier. Now, note that we are wasting transmitter power because in AM the carrier is transmitted -- as well as two sidebands with identical information. What if, then, the transmitter suppresses the carrier and one sideband (either the lower or upper -- it doesn't matter)? This results in single sideband operation -- the transmitter only transmits one sideband. This also has the benefit of conserving precious spectrum, since the SSB signal takes up less room than the wider AM (double sideband) signal. In a radio receiver, to demodulate (recover the voice message) from the RF signal (in this case, a sideband), a product detector is normally used. This detector requires a local oscillator (called a BFO), to recover the voice message from the carrier. There is normally a BFO Frequency tuning control on the receiver to properly adjust the BFO so that the voice is properly received. Standard AM reception does not require this method of demodulation. A single sideband signal received without the receiver set to SSB mode is unintelligible; you can make out that there is something there, but it sounds muffled and unreadable. Tune the receiver to one of these signals, then switch to SSB mode. If the BFO tuning is off, the voice will sound like a "Donald Duck" voice -- use the BFO tuning to adjust to a normal-sounding voice. For more information on modulation or radio in general, refer to some of the American Radio Relay League publications. Brian K. Daly WB7OML UUCP: {...!ames!ncar!noao!asuvax|uunet!zardoz!hrc|att}!gtephx!dalyb AG Communication Systems, PO Box 52179, Phoenix, Arizona 85072-2179 Phone: (602) 582-7644 FAX: (602) 582-7111