PLL Wars

The battle over which radios ruled the roost for maximum channel expansion.

Within the local cast of characters who made up the CB radio hobby in our area, there comprised a handful of people who were not only technically curious about the inner working of their radios, they were always looking for new and innovative ways to improve their radio's performance and capabilities. More power, and louder modulation were two of the biggest areas to pursue these goals. Another area which was extensively explored, was frequency expansion. It was desirous for the high performance radio operator to have more channels than the "common folk" had, whether simply for a private escape channel, to increase one's DX opportunities, or simply for local bragging rights. But the pursuit of these expansions were usually not all that easy, or cheap. In the early 70's, the typical 23 channel radio generated its frequencies by mixing different combinations of crystals. In order to expand frequencies on these rigs meant that you had to either add additional crystals for more channels, wire in a VFO to add continuous wide range tuning, or experiment with other tricks like expanding the clarifier range or reversing mixer crystals. While all of these solutions were popular, none were a clean simple operation to perform, nor were they inexpensive. And when you were a strapped for cash teenager, expense was a definite consideration. But those were the limitations of the crystal synthesized radio of the 60's and early-mid 70's. So it should be no surprise that most people had only a limited number of extra channels to sneak away to. But advances in technology were about to change all of that in a big way. And the CB band would never be the same........

The first hint that something new and different was about to hit the market came about in the 1974-1975 timeframe. The Hy-Gain 623 and a couple other radios hit the streets sporting a new high tech "digital" synthesizer. A handful of I.C. chips replaced the usual bank of 12 or 14 crystals. As time progressed, other manufacturers followed with similar PLL schemes as well. It would seem that most of the major manufacturers were experimenting with this new technology on at least one model in their radio stable. At first, most of us looked at these "newfangled" PLL circuits with disdain. They could not be modified in the usual familiar way to get the expanded channels that we were all used to running on. Even trying to put channel "22A" in the blank spot did not yield the same results as we expected. But our dismissive prejudice, based on nothing more than ignorance toward the PLL, only blinded us to their ultimate potential, even if the early units were not nearly as capable as later designs. But soon people started accidentally discovering some strange behavior on some of these newfangled PLL rigs. It was discovered that when the channel selector dial was wiggled carefully between certain channels of their radios, new channels would appear that were outside of the 23 channel band plan. Several RC channels, as well as future channels 24, 25, 26 and 27 were among those channels discovered. All of a sudden, the PLL became interesting, and those techies among us scrambled to discover what other secrets might lie within that mysterious circuitry. But before any of us could seriously experiment on them though, we had to find out how they worked. The internet didn't exist yet, and the eventual proliferation of "How-to" CB theory books hadn't been written yet, so there wasn't a wealth of knowledge on the subject. So for me, the first light to shine into the dark place that was the PLL synthesizer, occurred in 1976. A Channel 6 local by the handle of Windbreaker (who was a physicist by trade) offered to explain the binary counting system to me. He explained that the PLL was programmed by binary numbers, and that the total number of combinations (channels) could be determined by the number of programmable pins, and using that number as the exponent of the number 2. In this way a radio with 5 control pins would be 2^5 which equaled 32. Similarly, 6 control pins (2^6) would yield 64 channels. Interesting...... So it made sense that when you totalled up the frequency range from channel 1 to channel 27 (including the "RC" channels) it equaled 32 combinations. So since the closest binary number that could handle all 23 channels was 32, those early 23 channel PLL rigs could add an additional 9 channels, via the programming of the PLL chip, without the need to add crystals. Armed with this new information, I was ready to start experimenting. There was only one problem, I didn't own a PLL radio of my own to play with. Enter LIM (Tom). Tom was a good and trusting friend at the time and owned a newly acquired Midland 13-830, a mobile radio which looked a lot like the 13-862, but was a 2nd generation 23 channel Cybernet PLL design. By 1976, the new PLL designs had become considerably simpler. Where the initial designs used several I.C. chips to form the PLL, the latest designs had reduced this number down to a single PLL chip. And it was in this particular radio, where I was first introduced to the venerable PLL-02A PLL chip. The first thing I did was to create a "truth chart", by measuring the 5 control pins which went to the channel selector and stepping through each channel on the dial. When that was done, it became easy to see where "skipped channels" were, as well as the 2 extra channels above 23 (26, 27). Putting a switch on key pins enabled the user to alter the programming that the channel selector provided to access frequencies other than what the FCC wanted us to have. While testing out this neat but somewhat restricted amount of extra channels, I also noticed that there were 2 other pins next to the ones attached to the channel selector, that were pulled high (5V). On a hunch, I unsoldered the adjacent pin, and the radio's receiver died. But then I tried it on the highest programmable channel, and the receiver stayed on. Using a tunable receiver (a frequency counter was way outside of my price range in those days), I determined that I was now one channel below channel 1. Expanding on the truth chart, I predicted where the frequencies would be, and upon checking, my predictions were correct. So it looked like I found another programming pin, and 32 more channels below 1. But not all of them worked. At some point, the radio stopped working. I wasn't sure what was happening, but the PLL appeared to have a limit to how many channels you could generate. After borrowing the SAMS Fotofact for the radio and looking at the alignment procedure, I became aware of the Voltage Controlled Oscillator (VCO), which was tuned by a voltage depending on the frequency desired. It appeared that the oscillator had bottomed out, and could not tune any lower at the current setting. The good news is that the voltage range was centered by a variable coil, so I figured it should be possible to shift the tuning range by adjusting this coil. So returning to the channel that made the radio cut out, I turned the VCO coil ever-so-slightly one way, and then the other. Sure enough, the receiver came to life again, and I could drop another handful of channels before the radio cut out again. But another tweak of the VCO brought it back again. While experimenting with my newly discovered lower channels, I ran across a couple of local guys who were talking away about 10 channels below 1. I broke in to say "Hi", and they were surprised to hear me down there, and were curious as to what I had done to get there. Needless to say, what I had done was a heck of a lot cheaper than what they had to do to accomplish the same feat. Around this time, the pending 40 channel band expansion had become public knowledge. But try as I might, I could not get Tom's Midland to go above channel 27. It seemed lopsided to have all those channels below 1, but not the soon-to-be-legal additional 13 channels higher than the Midland currently tuned. It was frustrating to say the least. It would be another couple of years before I would discover the last 2 programming pins (7&8, which were on the other side of the chip), which would have allowed movement above channel 27. But for the time being, Tom was content with his 9 in-band, and 32 below extra channels.

I was also introduced to another PLL IC equipped radio, in the form of a Sears 23 channel Roadtalker. This radio used a different PLL, a uPD-861. Using what I had learned, I scoped out a truth chart, and I was soon scratching my head. This radio had no gaps in the truth chart for the "A" channels, but did have other gaps that made no sense, all the way up to channel 23. But there was an open control pin, and a single added switch allowed frequency expansion all the way up to soon-to-be channel 39 (Channel 40 required all pins to be at 0), but nothing beyond, even when additional combinations were tried. This was my first experience with a BCD programmed ROM restricted PLL. I didn't understand what was happening with that PLL then, and I just made a note that this chip was "weird".

On January of 1977, the FCC authorized the expansion of the CB band from the original 23 channels, up to the current 40 channel plan. New 40 channel radios soon flooded the streets and nearly every one was a PLL controlled frequency synthesizer. I still couldn't afford a new 40 channel PLL radio of my own yet, but I soon started modifying the radios of friends who had bought Lafayette and Midland PLL-02A equipped radios. On the 40 channel versions, the design had changed a bit. There was one less loop mixer crystal, and the truth chart was different from the older 23 channel chassis. On these Cybernet 40 channel AM radios, utilizing the 7 known (at that time) control pins, would yield a range from 53 channels below 1, all the way up to channel 70, for a total of 128 channels. That was a fairly decent amount of extra channels to be had for little more than the purchase of 3 SPDT-center off switches. Royce radios were also popular, but the PLL in those was good for only 64 combinations which took the radio from channel 1 up to channel 59.

Back in 1977, we didn't have the internet to search for information, we didn't even have datasheets yet for the various PLL chips which began appearing in new radios. Instead, we had to rely on our own experimentations, and those of other guys. But we did start rating different radio brands based on the capabilities of the PLL chips inside their radios. Some of these ratings would change if an additional capability was "discovered" by someone tinkering with their rig. At the top of the list of favorite PLL chips had been the aforementioned PLL-02A. But another chip soon entered the fray and challenged the 02A for the top spot in the PLL expansion contest........ Enter the Uniden uPD-858. I first ran across this chip in a Realistic TRC-152 , a PLL controlled 23 channel radio that I obtained from a local and it had been the victim of a lightning strike. Because I wanted a PLL radio of my own, I put in the extra effort to get the rig running again. And once it was, I began to experiment with the PLL. Like before, I started off with a truth chart. Like the uPD-861, this chip counted in a strange sort of binary that was not consecutive. But unlike the uPD-861, it did have channel skips for the "A" channels. Noticing that there was a place for another control pin to be added (presumably for the 40 channel version), I added a switch for it as well as other pins. I was able to go up to channel 53, along with few channels below one, before the VCO would quit. While it was a nice range, it was not as good as the PLL-02A rigs.

As the years advanced, other chips were introduced. The MB-8719, the TC-5080, the SM5104 etc. Each of these allowed a decent amount of extra channels to be added. But still none could touch the 2 top dogs of the PLL battlefield, the PLL-02A and the uPD-858. In the current battle, the PLL02A was represented in a Cybernet SSB chassis, such as a Lafayette Telsat SSB-140. While the uPD-858 was installed in the Uniden SSB chassis found in brands like Realistic, Cobra, Courier, and President. And each local tech had their favorite radio to experiment on, and it became a sort of friendly rivalry to see who's radio could operate on the most channels. It was a back and forth "one-up" contest with the channel limits being upped almost weekly. At first the 02A radios, with the discovery of extra control pins 7 & 8, which gave range clear into the lower part of the 10 meter ham band as well as travel below channel 1, had earned the top spot. The initial problem with the 858 chassis radios was that they ran out of "steam" (power and receive sensitivity) before their VCO range limits were hit. So while the 858's VCO could tune further, the radio wouldn't play well at the extremes. But then a broadbanding trick was discovered, where you moved the trace from the center tap of the coil to the outer pin on a couple of the intermediate stage tuning cans, which greatly increased the usable operating range. This trick broadbanded the radio significantly, and it would now go down as far as 26.085, all the way up to the voice portion of the 10 meter band, and still hold power. It also turned out that the VCO on the 858 radios would cover over a 2 Mhz spread, which exceeded the 02A radio's range. We also finally solved the mystery of the strange tuning jumps on the uPD-858. It turns out that this chip (and its cousin the uPD-861) was programmed, not by straight binary, but by BCD (Binary Coded Decimal) words. In BCD only the numbers 0 thru 9 are valid. Programming values other than that range result in an illegal value. But the chip would program channels even when those illegal numbers were forced into it, which had us scratching our heads. But when programmed correctly, the chip was capable of a total of 399 10 Khz-spaced channels (it could also be set to tune in 5 Khz steps) of which over half could be tuned at a time. I learned even more about the PLL-02A in that time as well. And when the smoke finally cleared, the number of known control pins had increased from the original 7, up to 9 with a total frequency count coming in at a whopping 511, but the VCO range was limited to less than half of that (without some determined modifications).

The final head-scratcher to be solved was that "weird" uPD-861. I had first come across that chip early on, in a couple of 23 channel Sears Roadtalker radios, and discovered that they weren't mod friendly and would not tune any out of band channels. Without any datasheet or evidence to the contrary, I had pretty much written this chip off as "unmodifiable". But in 1978, I got my hands on a Realistic TRC-431. Inside, nestled under a protective shield, was the uPD-861. I had been told that these radios could be modified, but previous experience with this chip had me skeptical. Imagine my surprise when this radio's channels counted in straight binary, had RC gaps, and could be expanded. The range of this radio, was unfortunately very lopsided, with an upper limit of channel 57, and a ton of channels below 1 (upper end of 25 Mhz before the VCO quit). So what was the deal? How could the same I.C. program so completely differently in different radios? I also had at the time a Realistic Mini-40, which utilized the '861 in the same fashion as those earlier Sears Roadtalkers did. So I started comparing the pins of the chip on the schematic with the TRC-431's, and discovered that there was a programming mode pin which could select an "open" 8 bit binary mode, or a "closed" BCD 40 channel only mode. Toggling that pin on the mini 40 showed that I could indeed program out of band channels. But the BCD coded channel selector was totally wrong for the type of programming needed in the unlocked binary mode, so extra frequencies in that radio were not consecutive and there were many skips and gaps. In short, it was ugly. But another mystery had been solved.

The uPD-861, unfortunately, was a harbinger of things to come. The FCC, naturally, got wind of the explosion of radios being modified to go much further than radios used to go back in the days of VFO and crystal modifications, and do so with relative ease. They then mandated that new radio designs utilize "unmodifiable" PLL chips, which use an internal ROM to isolate the programming pins from direct control, allowing only the "legal" channels, which were coded in the ROM, to be valid. A handful of new chips were introduced, the uPD-2816, the uPD-2824, the LC-7190 and many others. Today, only a few legacy radios still utilizing a copy of the original Uniden MB-8719 design can be modified via the PLL. It's still possible to move other radios, but that involves "tricking" the PLL, and is neither as easy to do, nor does it utilize the same fantastic channel range as those original 40 channel radios did. But for a few years anyway, the sky was the limit and dozens of adventurous technical types truly did find their radio nirvana, with little more than a few switches, some wire, and sheer determination....