The voicelock (sometimes called 'clarifier') is needed for SSB. When operating in single sideband mode, it's important that you and the person you're talking to be transmitting/receiving dead on (or very close to dead on) the same frequency. When you get a chance, turn the radio on and see if you can find people talking in upper or lower sideband. If you can't find anyone, find some people talking in AM and set the radio to either USB or LSB. Then experiment with turning the voicelock knob. You should be able to hear people speaking, but their voices may be too high or too low in pitch until you get the voicelock knob set just right. When you do have it set just right, their voices should sound the same on USB/LSB as they do on AM.
Normally, CB rigs are designed to only transmit on a fixed set of 40 channels, and you're not supposed to be able to shift off frequency. That is, for channel 21, you're meant to transmit on 27.215 only. Not 27.213 or 27.217 -- 27.215. However, CB radios are generally cheaply made. This means they aren't very stable and not carefully calibrated at the factory. So there can be some variation: one radio might transmit on 27.215.00 as intended, but another might transmit on 27.215.23, another might transmit on 27.214.71, and so on. Also, they will sometimes drift as they warm up. For AM, this doesn't matter much, but for sideband, these differences in frequency can make it hard to understand someone as their voice will sound funny.
The voicelock control is intended to help you tune the receiver a bit to overcome this problem. If you're on LSB and someone sounds a little high pitched, you can adjust the knob a little until they sound normal. The guy on the other end is expected to do the same.
Note that if there's more than two people, this can get messy: you may have to set the voicelock knob in one place to properly receive one station, but set it somewhere different to receive the other.
Again, out of the box, the voicelock only tunes the receiver. The transmitter is supposed to stay locked on the center frequency for the current channel and not move.
When people modify radios, particularly the Cobra 148GTL, they'll do two things:
- Modify the radio to transmit on more than just the officially authorized 40 CB channels
- Modify the voicelock so that it fine tunes both the receiver and the transmitter together
This latter modification is called "unlocking" the clarifier. It means the transmitter is no longer locked right on the center channel frequency: you shift a little up or down by adjusting the voicelock. In other words, the now the voicelock doesn't just affect how you hear other people: it also affects how other people hear you.
Exactly how far up or down you can tune the voicelock varies a bit from radio to radio. You usually have at least +/- 5Khz. That means if the center channel frequency is 27.215, you can use the voicelock to adjust down to 27.210 and up to 27.220. At 27.210, you'll be right between channel 20 and 21, and at 27.220, you'll be right between channel 21 and 22. This is called "sliding in between channels." Sometimes people do this to impress the newbies, or to get away from obnoxious operators.
It's customary to design the voicelock circuit so that you will be right on center frequency when the knob is set dead center at 12 o'clock. Turning clockwise shift you up in frequency and turning counter-clockwise shifts you down. If you have it set fully clockwise, you may actually be operating a bit too high in frequency. Again, you may not notice this on AM. However, with the Cobra 148GTL, the voicelock control _is_ active on AM. If your voicelock is "unlocked" they you may be transmitting off frequency. I would set the radio to USB or LSB as a test and adjust the voicelock knob to where voices consistently sound the clearest. It should be somewhere close to 12 o'clock. Once you find that spot, leave it there.
Note that in some cases, you may find that the voicelock has more range one way than the other (that is, it may shift farther down that up, for example). This is also something that varies from radio to radio. It tends to be more consistent with export radios that come from the factory with an unlocked clarifier. (Export radios come with the clarifier/voicelock unlocked in order to maintain the pretense that they're intended for use on ham radio bands to get them past the FCC. The ham radio bands are not channelized: you can operate on any frequency within a given band as long as you don't interfere with someone else. Without an unlocked clarifier, a typical export rig would only be of limited use on the ham bands, so it would be tough to classify it as a 'ham radio' for import purposes.)
-Bill
