Pages: (1) (2) (3) (4) (5) (6) (7) (8) Modulation page // Oscillator Page

(<-- continued from page 5)

Everybody rested up from going through the receiver? We're actually over halfway done, because a lot of the circuits we've walked through do double duty in both the transmit and receive parts of the trip.

We're sitting in the right place to start, since this time we'll follow the juice back from the microphone that's connected to that black cord we see running over the circuit board. See that big plastic container over there? That's the relay. The relay is a kind of switch which connects either the transmit or the receive circuits together. It's controlled by the push button on the microphone. That's how the parts common to both transmit and receive are switched back and forth from one to the other.

[Editor's note: Citizen's Band radios and many walkie talkies use a "push to talk" microphone which manually trips the relay. Cellular telephones use a voice activated transmitter which automatically trips the relay. Why the difference between the two? A cellular phone uses one frequency to transmit on and another one to receive on. This lets both callers talk in a normal, back and forth fashion, just like a regular land line telephone. The term is "full duplex communications." Since walkie talkies use a single frequency to both talk on and listen, each party must wait their turn to transmit. A voice activated microphone would not work well since you might start transmitting when the other party is speaking, consequently, you would not be heard. A push to talk button reminds each person that only one caller can talk at a time.]

Okay, everybody. Let's take a gander at our tour map so we all know where we're going. Let's stay together and not get lost through all these twists and turns. (Next page -->)

From The Big Dummy's Guide to C.B. Radio, courtesy of The Book Publishing Company P.O. Box 99,Summertown, TN 38483 (888) 260-8458, (1976). Editors: White Lightning (Albert Houston) WB4BWR, Stringbean WA4LXC (Mark Long), Minnesota Mumbler WB4KDH (Jeffrey Keating), Ratchet Jaw K4IAP (William Hershfield), Buffalo Bill WA4KCF (William Bradley) Illustrations by Mark Schlichting and Peter Hoyt.