CB PLL data book/en/Introduction
The Phase-Locked-Loop or „PLL” Frequency Synthesizer used in CB radios is a marvelous device. It can generate all the signals needed to run a complex transceiver, is more accurate than crystal control, and more reliable because fewer parts are needed. However, understanding its operation seems to cause a lot of anxiety among CB operators as well as professional technicians. It's the purpose of this book to explain in the simplest, most non-technical terms possible how the PLL works.
Anybody interested in the technical side of CB radio should find it quite helpful. I've tried to write this for both the casual CB hobbyist and the professional serviceman. CB radio is now a worldwide hobby. As an American who's seen it change from vacuum tubes to transistors, from crystal synthesizers to PLL synthesizers, I'm in a unique position to explain the PLL's evolution. While many of the circuits and IC „chips” detailed here are actually obsolete now, there are still a lot of those radios out there needing repair! And since most countries have limited CB operation to only 18, 22 or 40 channels, a lot of interest these days is in knowing how to expand a CB rig to cover more than the „legal” channels or frequencies. Many of the older rigs are actually much better for this purpose. There is also a lot of interest among ham radio operators in converting the CB into a 10-Meter Ham rig. I will explain in these pages how PLL repairs and modifications are approached. In many cases the changes are quite simple; it's no accident that a lot of American and European transceivers using certain PLL circuits are so popular even today. On the other hand, you may be very disappointed to find out that the most recent generation of IC chips for U.S., U.K., and European CBs were designed to be almost completely non-modifiable. Better keep that older rig if you have one!
Brief history and development
The main reason for the development of PLL synthesizers was the American CB service expansion from 23 to 40 channels in 1976. Until then CBs used a method of frequency generation called „crystal synthesis” or „crystal-plexing”. By electronically combining the signals of 2 or 3 quartz crystal oscillators in a common „mixer”, all the various Receive/Transmit signals (which are normally not the same) could be created with only 12 or 14 crystals for AM and a few more for SSB. This was a great savings in cost, circuit complexity and space, because otherwise at least 46 different quartz crystals would be needed, one pair per channel. There wasn't enough quartz left in the world to give it all to the CB manufaturers; they had to leave some for all those Seiko wristwatches!
With CB interest growing very rapidly, new methods were required because of the increased number of legal channels. Manufacturers had to figure out how to generate a large number of signals with a minimum of parts, space, complexity, and of course, cost. The answer was the PLL synthesizer. By the time the American FCC announced its CB expansion, „digital” electronic synthesizers were already well along. In fact the last generation of 23-channel U.S. equipment had already begun to use PLL techniques rather than crystals. Those first circuits were very complicated because they required as many as 9 discrete Integrated Circuit (IC) silicon chips. Soon more and more electronic functions were crammed into a smaller chip space. Today’s PLL transceiver can perform all the needed functions of channel selection and signal generation using only a single LSI („Large-Scale-Integration”) device and a handful of external parts. As we’ll see, this fact is both a blessing and a curse: Good because it increases reliability and keeps radio prices affordable, but bad because the darn bugs make modifications even harder!
The FCC and other authorities quickly found that because of the unexpected popularity of CB, with millions of people all competing for the same channels, the use of illegal and unauthorized frequencies was becoming the rule rather than the exception, and this is basically the situation today. Technicians soon discovered that the first generations of PLL rigs were simple to modify. The FCC then changed its rules to require CB manufacturers to use special PLL chips to prevent this. Since Australia, Holland, Britain, and other countries had legalized CB long after the U.S., their governments took the hint and started off directly with the more secure chip circuits. However through various legal loopholes, certain makes and models of CBs in the U.S. and other countries are still allowed to be imported using the „good” PLL chips, and this subject will be covered in great detail later.
In all fairness I should mention that the newest chips are capable of some interesting features not found in earlier generations. For example, automatic command of the Channel 9 Emergency Channel or Channel 19 Road Information Channel, scanning, memory, keyboard control, greater reliability, etc. This is basically where the state-of-the-art in PLL technology is today, and there is little more that governments can do to prevent any determined radio hobbyist from modifying a rig if he really wants to. I think it’s safe to assume that information in this book detailing operation of the latest PLL devices will be accurate for many years to come. And since there are still millions of older rigs out there needing maintenance, the amount of attention devoted to these older rigs is justified.
Book organization
I’ve divided this book into three general sections. The first section describes basic PLL theory in „building block” form. We’ll start with the simplest chips and proceed to the most complex, in chronological order because that’s the way they have evolved. In this way, you’ll begin to understand how the various IC changes affect servicing and modification. I’ll assume th at you have very little electronic knowledge, even though some of you may be very well- informed about other areas of CB electronics. The PLL circuits will only be illustrated in „black box” or block diagram form to keep things really simple. For example, a transistor switching circuit will be represented symbolically as a simple switch. Components like resistors, capacitors, etc. will rarely be shown at all unless very essential to the discussion. This way you’ll never have to worry that you’ve gotten in over your head! Specific radio theory regarding AM, FM, or SSB communications not directly related to the PLL are left up to you for further study if interested. Some very basic radio theory must be included, but I’ve tried to keep it very uncomplicated. Since I want everybody to learn something about this subject, some areas are oversimplified, and I ask th a t you professional technicians out there have a little patience if something seems obvious to you.
The second section deals with modification methods as they apply to different generations of PLLs. We’ll be discussing such things as Truth Charts, programming in binary, BCD and ROM, Loop Mixers, external oscillators, and tips on how to attack the various types of PLL circuits successfully.
The last section shows technical specs and block diagrams of the chips and circuits themselves. I’ve included every known chip of any importance. (There were a few very old chips that never lasted long enough to bother discussing.) To my knowledge this is the only book ever published devoted entirely to the subject of CB PLLs. Along with the chip pin diagrams is included a list of every radio make and model using that chip which was known at press time. Since several groups of chips work the same way, I’ve also included sample Truth Charts typical of such groups. I’ve tried to include special notations when a chip contains some unusual feature you should know about. All the specific pin functions were gathered from m anufacturers’ spec sheets, SAMS Fotofacts and other service manuals, and personal experience, and are accurate to the best of my knowledge. If you don’t find your particular rig model included here, chances are that it’s identical to some other rig, since there are basically now three Far East companies (Cybernet, Uniden and Maxon) that make 99% of the world’s CB radios anyway. One particular chassis may be sold under dozens of brand names as most of you already know. For certain well-known chassis, I’ve included specific PC board numbers so that you might possibly identify an unknown rig by that number.
My two trips to England and Europe in 1981 to study the CB situation there helped greatly in gathering the special circuit information found in these pages. Most Americans will never see the “export” models of their favorite radios; information on the addition of another 80-120 channels and FM should help your own modification attempts when you see how they’re done commercially. Information on the European versions of popular American rigs, as well as the newest „legal” U.K.- FM rigs, arrived just in time to appear in this book so that this is truly an international reference work. By press time, thousands of „export” rigs like the Cobra 148 GTL-DX, Palomar 2400, SuperStar 3600/3900, Galaxy 2100/Galaxy Super, and Ranger AR3500 had arrived in the U.S., and are included in Section III. (We have schematics on most of these if you need one.) In addition, the British CB system has changed over to the American FCC channel assignment. So UK radios are now using the American PLL chips anyway.
Obviously it’s very difficult (and expensive!) to continuously update a book like this as new models appear, but the basic information for understanding any PLL circuit you’ll ever see can be found here. I’ve personally managed to catalog literally thousands of makes and models over many years by the use of SAMS Fotofacts, factory service manuals, and schematics sent to me by my readers. I’m always anxious to add new radio models to my files for possible future revisions and to help my readers identify a specific chassis or PLL circuit. Photocopies of rig circuit diagrams are always appreciated. I welcome your comments and suggestions and hope this book helps you.
Good luck in the Battle Of The PLL!
Phoenix, Arizona, U.S.A.
Lou Franklin, K6NH
„Supersparks”