This guest post is by Michael C and entry in our non-fiction writing contest .
Single Side Band (SSB) transmission is available on higher end CB radios and of course, in ham radios that support the mode. Think of the “mirrored sine wave” cut in half. That half of the signal uses less than half as much power. Also, lets get rid of the carrier so that if there is no sound, even though you are keyed up, there is no signal. All CB radios transmit at 4 Watts of power (per FCC regulation) but on side band that amounts to 12 Watts since the “average” of the sine wave (for a half height signal) is used. Radios that have SSB have a choice of USB or LSB (Upper/Lower Side Band) which does allow for double the number of channels for CB’s. Ham radios don’t have near as much of a channel crunch with thousands of options.
SSB is really a “person to person” mode because both operators must “fine tune” their radio to each other. It goes something like this; first radio operator gives a count of ten and the second operator twists the fine tune knob until the first operator does not sound like a chip monk and not like “Jabba the hut” either. The second operator then gives a count of ten while the first operator tunes in. A third operator cannot participate since he can only tune in to one or the other operator, then the other operator sounds like a chip monk or “Jabba the hut”. The third operator also sounds odd to BOTH of the first operators since neither is tuned in to him/her.
The circuits that made radios better, more reliable, also allowed higher frequencies to be used. Electronics allowed the signals to be manipulated in ways not done before. The FM (Frequency Modulation) transmission mode varies the “frequency” of the wave with change in sound.
I’ll use FM stereo radio (88-108 MHz) as an example. It works like this – start with a base line frequency like 100.1 FM then add the audio count (20-20,000 Hertz) to the base (100.1+20,000=100.12) to get a transmit frequency.
The right channel (radios are south paws) of the stereo signal is subtracted from the base and transmitted separately. There is no stereo mode for ham radio. FM broadcasts have very high fidelity compared to AM broadcasts. Lightning does not make FM crackle like it does AM. This is because lightning cannot affect the frequency, only the amplitude or power.
An early problem was FM drift in which the FM signal “drifted” out of frequency – PLL (Phase Locked Loop) circuits corrected this. In fact most ham radios have digital tuning. FM transmission is the dominant method for frequencies above 29 MHz. You’ll also notice something nice about the FM signal – it’s constant strength. The power (amplitude) does not change like AM does. AM transmissions are low frequency which means big waves and big antennas.
The big waves can travel a long distance as “ground waves”. The AM waves can “circle the globe” by reflection off the ionosphere which occurs mainly at night. Sky wave bouncing is an interesting subject in itself but since most people are going to start as a tech – all of the bands that you will be allowed on are “line of sight” bands. You would have to become a General (ham license) to operate on HF bands then you would already know about bouncing your signal.
This contest will end on December 16 2012 – prizes include:
- First Place winner will receive a Go Berkey Kit valued at $150.
- Second Place: $100 Cash.
- Third Place: $50 Cash.