Common Radio Features
If there is one thing about the different makes and models of CB radios that determines their perceived value and overall consumer appeal, it is the amount of user features, or "bells and whistles" as they are more commonly referred to, that are included as standard equipment. The degree of complexity and sheer amount of user functions ran the gamut from simple basic minimal controls, all the way up to radios which included all sorts of knobs and switches. Some of these functions served a valuable and necessary purpose, and could enhance the functionality and usability of the radio. Others "features" were little more than advertising hype, used to justify a premium price, which was usually higher than the radio was actually worth, all other things being equal.
But what were these numerous features, and what did they actually do? I'll attempt to explain those common (and not-so-common) features which graced the front panels of the common CB radio from back in the day. This list of features will start with the most necessary, and work down to the most trivial. Since this is based from my own perspective, I'm sure others might disagree with their exact placement on the list, but here they are:
Common Control Features:
Volume - Probably the most common and necessary feature. I don't know of a single radio that didn't have one (With the exception of some cheap 100mW walkie-talkies, but they don't count!). The volume, quite simply, adjusts the level of receive audio.
Channel Selector - Except for single channel radios, every other type had some sort of channel selector switch. It could be 3, 6, 8, 12, 23 or 40 channels. Some radios had separate selectors for transmit and receive, with the receiver selector sometimes being a variable tuner, similar to that found on a broadcast radio. The channel selector, as the name implies, selects the frequency (channel) that the radio operates on.
Squelch - The squelch is the last of the standard features typically found on "bare bones" radios. Some early tube rigs didn't even have one, but almost all fairly modern CB rigs did. The squelch control is a circuit which would "quiet" the receiver when no signals were present, thereby removing the receiver's inherent, and sometimes annoying "hiss". There are typically two different types of squelch circuits in common use. One method works by setting the receiver quiet threshold by signal level (usually referred to as a "carrier squelch"). The other type sets the quiet level by signal to noise ratio (referred to as a "noise squelch"). Most CB squelches are of the "carrier" type. A decent communications grade FM transceiver will usually have a "noise" type.
ANL/N.B. - Stands for "Automatic Noise Limiter/ Noise Blanker". These features are sometimes combined and sometimes found on separate switches. Cheaper radios may have the feature enabled all the time, with no switch. What these functions are, are methods to reduce noise from a receiver that would otherwise interfere with desired signals. Unlike a Squelch, which simply silences the receiver at the level of the noise, the ANL/NB actually attempts to reduce the noise somewhat. The ANL simply rectifies or clips "hash" noise, making it less noticeable, and therefore less objectionable. It can also alter (distort) the receive audio slightly when on. The Noise Blanker circuit is a bit more sophisticated. The N.B. momentarily turns off (blanks) the receiver for the duration of pulse-type noise, such as that caused by automobile spark plugs. The net effect is that the noise pulse is removed from the signal, and the operator does not hear it. An effective Noise Blanker can make the difference between a so-so radio, and a great receiving radio, especially in a mobile. Noise Blankers can increase bleed over when on, so many operators leave them off unless they're getting high noise levels.
Mode Switch - The mode switch is only found on multi-mode (SSB/AM) radios. This control simply selects AM, Upper Sideband, or Lower Sideband.
Clarifier - The Clarifier is an incremental fine tuning control which is necessary to home in on the precise frequency of a SSB signal so as to make it sound legible. The tuning range of the Clarifier was usually in the +/- .8 to 1.2 Khz range. On most older 23 channel rigs, this control shifted both the receive and the transmit frequency synchronously, allowing several people to "net" themselves onto the same exact frequency. On newer 23 channel radios, and all 40 channel radios (that I've ever seen) the clarifier only moves the receive frequency. This control is also known by proprietary trademark names, such as "Voice Lock", and "Slide-o-Tune".
R.F. Gain - The R.F. Gain is usually found on SSB radios, but was also occasionally found on some AM-only units as well. The job of the R.F. Gain is to reduce the sensitivity of the receiver through a variable control. This was helpful when talking to strong local signals who may overload your receive. It was also handy for making more precise comparative signal checks between local signals. It was also used in lieu of, or in addition to, the squelch for quieting a receiver.
Local/Distance - Similar in purpose to the R.F. Gain, except that instead of a continuously variable control, it uses a 2 position switch. "Distance" enables full receiver sensitivity, while "Local" set the receiver to a much lower (and fixed) sensitivity.
Delta Tune - The Delta Tune was a curious name for a receiver tuning feature, similar to a Clarifier, but found on AM-only rigs. Usually this was a 3 position switch with a middle position, a "-" and a "+" position. When in the center position, the receiver was "on frequency". When in the "-" position, the receiver shifted down a Khz or so. The "+" shifted the receiver the same amount, but higher in frequency. This was a common feature on older rigs, as FCC specs for frequency tolerance were not as strict, and this feature could improve reception of those other stations which were a little off-frequency. The advent of PLL frequency synthesizers, in modern rigs, has pretty much rendered this function obsolete.
Fine Tune - Similar to a Delta Tune, except that a Fine Tune is typically a continuously variable control instead of 3 position. Some manufacturers used gimmicky sounding names for it, such as "Receive-o-Slide".
Mic Gain - The Mic Gain control adjusts the sensitivity of the radio's microphone input. In theory, this was to compensate for people who spoke softly versus those who talked loudly. In reality though, this control was usually set to maximum unless an external amplified mike was used. This control was also known by marketing names such as "Dynamike" and "Range Boost" among others.
SWR Calibrate - This control is only found on radios with an SWR meter function. The purpose of this control is to set the forward power reference point (Usually at the end of the meter's scale), to "calibrate" for the SWR reflected power reading.
FWD/REF - Works with the SWR calibrate. Switch to "FWD" to calibrate the meter. Then switch to "REF" to see the SWR reading.
P.A. Switch - The P.A. or Public Address function allowed the radio's audio amplifier to direct your voice through an external speaker, rather than transmitting over the air.
P.A. Volume - Works with the P.A. switch. The P.A. Volume or Gain adjusts your level of P.A. loudness. Some radios used the regular Volume control for this function. Fancier radios utilize a separate control.
EXT Switch - Sometimes found as a position on the channel selector, and sometimes as a separate switch. This function allows you to use your CB as an audio amplifier.
Spot - The spot control is found on rigs with variable tuning receivers. The spot enables the operator to set his receiver tuner to the transmit frequency he is on by sending a very low power signal from the transmitter, which the operator then tunes the receiver to.
Multi-Channel Monitor - Some radios had the capability to simultaneously monitor two channels at once. Some had a fixed channel 9 (The emergency channel) monitor, while others allowed you to select the "other" channel. The radio would alternately scan between the two set channels, and would lock to whichever channel had a signal. On some radios with strictly channel 9 monitors, if a signal appeared on channel 9, you had the choice of automatically switching there, or flashing an indicator lamp alerting you to the presence of a signal on channel 9.
Channel Scan - Some of the fancier 40 channel radios had the ability to scan all 40 channels. Usually you could scan for either "clear" or "busy" channels. When scanning for busy channels, the radio would simply stop on the first channel where a signal would break the squelch level. The clear scan was just the logical inverse of this. The radio would only scan when there were signals present.
Tone - Like on a broadcast radio, the tone control adjusted the fidelity of the received signal, usually by attenuating the higher frequencies.
Dimmer - Sometimes the radio was used in bright light, other times in a dark room. The dimmer compensates for this by allowing the operator to adjust the brightness of the indicator lamps on the radio.
T.T.C. - Stands for "Transmit Tone Control", this control was found only on a few high end radios (The Tram D201 and D201A and Demco Super Satellite). Similar to a receiver tone control, except that this one adjusted the tone of the transmit signal. This was great for compensating for overly "tinny" or "bassy" sounding microphones.
Antenna Load/Tune - Found mostly on tube radios, the antenna load/tune were the Pi matching tuners, which matched the impedance of the transmit final to the antenna's load impedance, allowing for maximum power transfer. These controls were usually found on the back panel of the radio.
TVI - Another "back of the set" adjustment, the TVI control adjusted a trap which filtered out the 2nd harmonic of the transmitter, to minimize television interference. This was not normally considered a user control except for the fact that on some rigs, it was accessible from the back panel
A.G.C. - Stands for "Automatic Gain Control". Almost all radios have this feature built-in. The purpose of an AGC is to regulate the receive volume to a nearly constant level regardless of variations in R.F. signal level. It does the job fairly well in most cases. But at least one radio (Royce 640) had a switch where you could turn off the A.G.C.. I can't imagine a situation where someone would desire to do this. But hey, it looked good on the brochure.
5W/100mW - Some older (early-mid 60's) Lafayette (And possibly others) tube rigs had a switch on the back panel which allowed you to select between the full 5 watt R.F. power input, and a 100 mW low power position. At the time, the makers tried to advertise this as a means to "instantly use" your new radio before the FCC processed your license application (which could take several weeks), by operating it at the low power setting and thereby allegedly conforming to FCC Part 15 no-license rules. The FCC threw cold water on this idea when they subsequently revised their rules and required Part 15 radios to mandate that the antenna and transmitter be self contained in the same package (IOW: A walkie-talkie) and no longer than 5 feet long. The 5W/100mW switch disappeared from the scene shortly after that.
Alarm - Some older Lafayette mobile rigs (and maybe others) had this feature where a switch contact was connected to one of the mobile mounting bracket screws. A pair of wires sticking out of the back of the radio were then supposed to connect to an alarm or the car's horn, and if a thief were to attempt to remove the radio, the switch would close, sounding the alarm. In my opinion, this was probably the lamest "feature" I ever saw, since anyone thinking about stealing the radio, would likely cut the wires first, which would effectively defeat this "protection".
Channel - Most 23 channel radios and the oldest 40 channel radios simply used an illuminated number dial attached to the channel selector switch. Newer 40 channel radios utilized an pair of 7 segment LED indicators to show which channel you were operating on, which was far easier to read.
Meter - Most decent radios had at least one multi-function meter. On small mobile rigs, the meter was often very small and hard to read. On base stations, though, the meter could be quite large and easy to read. On receive, the meter indicates signal levels in 6db increments known as "S" units. On transmit, the meter indicates relative power output. Additional meter functions include Standing Wave Ratio (SWR) and Modulation measurement capability. Sometimes these features are switched via a front panel switch. Alternately, there may be separate meters for these features. One radio (the SBE Console V), actually had a meter to indicate the squelch level (Why?). Marketing gimmicks at their finest, I would guess. Radios made in later years have shifted away from analog meters and gravitated toward LED "Bar Graph" style indicators. I never liked these as they are not as precise, and lack the fine granularity of a D'Arsonval analog movement.
Clock - Some of the nicer base station radios included a clock. On some, the clock simply indicated the time only. While on others, a turn-on or turn-off and alarm functions were included as well.
Modulation - Usually a modulation indicator was a small lamp or L.E.D. which flashed when you talked. It wasn't as precise as a modulation meter, but it could tell you at a glance whether on not you were "talking".
Mode - Some radios had illuminated indicators to let the operator know what mode they were on. This was handy when operating in the dark (like in a mobile).
Frequency Counter - Only a few premium radios had this feature. A Frequency Counter tells you precisely what frequency you are on. But unless you were an avid SSB'er and/or ventured onto illegal channels, this was pretty much a superfluous feature. But it looked cool in any case.
A.W.I. - While the modulation indicator was the "idiot light" compared to the modulation meter, the A.W.I. or Antenna Warning Indicator, was the "idiot light" compared to an SWR meter. Usually the A.W.I. was set to illuminate when the radio's antenna system reached a predetermined SWR level (Usually between 2.5:1 to 3:1). Sometimes called the "SWR Alert".