Midland 79-892 40 channel SSB with pll02a chip

[Night Ranger]

I was looking around the web at all the various web pages that mention the Midland 79-892 am/ssb CB and the pll02a chip. The first thing I noticed is they are all direct copy and paste copies of each other. In the pll02a truth chart Channel 20 on all pages is listed with a incorrect entry of 27.005 MHz instead of 27.205 MHz. The pll02a data may be otherwise correct for other pll02a radios, but the truth chart in the Midland 79-892 service manual as well as the Sams Photofact (CB-180) are completely different from what the web information claims for the Midland 79-892

(Note I list the binary numbers in the correct highest bit to lowest bit ordering where as the web pages list the binary numbers in an incorrect lowest bit to highest bit ordering. You'll need to reverse the binary numbers they present to the numbers I present to make a comparison. Also since pins 7,8,and 9 do not change value on a stock Midland 79-892, they are not listed in the Midland 79-892 service manual truth chart or the Sams Photofact truth chart).

The various pll02a web pages claim channel 1 (26.965) is as follows;
===================================
CODE FREQ BINARY
===================================
330 26.965 101001010
===================================

but the Midland 79-892 service manual and the Sams Photofact for the Midland 79-892 (CB-180) claims;

====================================
PLL02a chip codes for Midland 79-892
====================================
CODE FREQ BINARY
------------------------------------
255 26.965 011111111
------------------------------------

So...for those looking to mod the Midland 79-892 and wondering why the web page information for the 79-892 does not match what the radio actually does, here is the correct information for the Midland 79-892 for the CB band channels.
====================================
PLL02a chip codes for Midland 79-892
====================================
CH CODE FREQ BINARY
pll02a pin #> 789abcdef << == hexadecial
---------------------------------------------------------------
1 255 26.965 011111111
2 254 26.975 011111110
3 253 26.985 011111101
4 251 27.005 011111011
5 250 27.015 011111010
6 249 27.025 011111001
7 248 27.035 011111000
8 246 27.055 011110110
9 245 27.065 011110101
10 244 27.075 011110100
11 243 27.085 011110011
12 241 27.105 011110001
13 240 27.115 011110000
14 239 27.125 011101111
15 238 27.135 011101110
16 236 27.155 011101100
17 235 27.165 011101011
18 234 27.175 011101010
19 233 27.185 011101001
20 231 27.205 011100111
21 230 27.215 011100110
22 229 27.225 011100101
24 228 27.235 011100100
25 227 27.245 011100011
23 226 27.255 011100010
26 225 27.265 011100001
27 224 27.275 011100000
28 223 27.285 011011111
29 222 27.295 011011110
30 221 27.305 011011101
31 220 27.315 011011100
32 219 27.325 011011011
33 218 27.335 011011010
34 217 27.345 011011001
35 216 27.355 011011000
36 215 27.365 011010111
37 214 27.375 011010110
38 213 27.385 011010101
39 212 27.395 011010100
40 211 27.405 011010011
====================================

I don't know how far up or down the pll02a chip in the Midland 79-892 will actually resonate (at least not yet), but below is the maximum possible binary combinations for the pll02a in a Midland 79-892 utilizing pins 7 through 15. I used hexadecimal numbers as place holders at the top and bottom of the list to indicate pin numbers on the pll02a chip (7 through "f" for pin numbers 7 through 15).

====================================
PLL02a chip codes for Midland 79-892
====================================
CODE FREQ BINARY
pll02a pins 789abcdef
------------------------------------
511 24.405 111111111
510 24.415 111111110
509 24.425 111111101
508 24.435 111111100
507 24.445 111111011
506 24.455 111111010
505 24.465 111111001
504 24.475 111111000
503 24.485 111110111
502 24.495 111110110
501 24.505 111110101
500 24.515 111110100
499 24.525 111110011
498 24.535 111110010
497 24.545 111110001
496 24.555 111110000
495 24.565 111101111
494 24.575 111101110
493 24.585 111101101
492 24.595 111101100
491 24.605 111101011
490 24.615 111101010
489 24.625 111101001
488 24.635 111101000
487 24.645 111100111
486 24.655 111100110
485 24.665 111100101
484 24.675 111100100
483 24.685 111100011
482 24.695 111100010
481 24.705 111100001
480 24.715 111100000
479 24.725 111011111
478 24.735 111011110
477 24.745 111011101
476 24.755 111011100
475 24.765 111011011
474 24.775 111011010
473 24.785 111011001
472 24.795 111011000
471 24.805 111010111
470 24.815 111010110
469 24.825 111010101
468 24.835 111010100
467 24.845 111010011
466 24.855 111010010
465 24.865 111010001
464 24.875 111010000
463 24.885 111001111
462 24.895 111001110
461 24.905 111001101
460 24.915 111001100
459 24.925 111001011
458 24.935 111001010
457 24.945 111001001
456 24.955 111001000
455 24.965 111000111
454 24.975 111000110
453 24.985 111000101
452 24.995 111000100
451 25.005 111000011
450 25.015 111000010
449 25.025 111000001
448 25.035 111000000
447 25.045 110111111
446 25.055 110111110
445 25.065 110111101
444 25.075 110111100
443 25.085 110111011
442 25.095 110111010
441 25.105 110111001
440 25.115 110111000
439 25.125 110110111
438 25.135 110110110
437 25.145 110110101
436 25.155 110110100
435 25.165 110110011
434 25.175 110110010
433 25.185 110110001
432 25.195 110110000
431 25.205 110101111
430 25.215 110101110
429 25.225 110101101
428 25.235 110101100
427 25.245 110101011
426 25.255 110101010
425 25.265 110101001
424 25.275 110101000
423 25.285 110100111
422 25.295 110100110
421 25.305 110100101
420 25.315 110100100
419 25.325 110100011
418 25.335 110100010
417 25.345 110100001
416 25.355 110100000
415 25.365 110011111
414 25.375 110011110
413 25.385 110011101
412 25.395 110011100
411 25.405 110011011
410 25.415 110011010
409 25.425 110011001
408 25.435 110011000
407 25.445 110010111
406 25.455 110010110
405 25.465 110010101
404 25.475 110010100
403 25.485 110010011
402 25.495 110010010
401 25.505 110010001
400 25.515 110010000
399 25.525 110001111
398 25.535 110001110
397 25.545 110001101
396 25.555 110001100
395 25.565 110001011
394 25.575 110001010
393 25.585 110001001
392 25.595 110001000
391 25.605 110000111
390 25.615 110000110
389 25.625 110000101
388 25.635 110000100
387 25.645 110000011
386 25.655 110000010
385 25.665 110000001
384 25.675 110000000
383 25.685 101111111
382 25.695 101111110
381 25.705 101111101
380 25.715 101111100
379 25.725 101111011
378 25.735 101111010
377 25.745 101111001
376 25.755 101111000
375 25.765 101110111
374 25.775 101110110
373 25.785 101110101
372 25.795 101110100
371 25.805 101110011
370 25.815 101110010
369 25.825 101110001
368 25.835 101110000
367 25.845 101101111
366 25.855 101101110
365 25.865 101101101
364 25.875 101101100
363 25.885 101101011
362 25.895 101101010
361 25.905 101101001
360 25.915 101101000
359 25.925 101100111
358 25.935 101100110
357 25.945 101100101
356 25.955 101100100
355 25.965 101100011
354 25.975 101100010
353 25.985 101100001
352 25.995 101100000
351 26.005 101011111
350 26.015 101011110
349 26.025 101011101
348 26.035 101011100
347 26.045 101011011
346 26.055 101011010
345 26.065 101011001
344 26.075 101011000
343 26.085 101010111
342 26.095 101010110
341 26.105 101010101
340 26.115 101010100
339 26.125 101010011
338 26.135 101010010
337 26.145 101010001
336 26.155 101010000
335 26.165 101001111
334 26.175 101001110
333 26.185 101001101
332 26.195 101001100
331 26.205 101001011
330 26.215 101001010
329 26.225 101001001
328 26.235 101001000
327 26.245 101000111
326 26.255 101000110
325 26.265 101000101
324 26.275 101000100
323 26.285 101000011
322 26.295 101000010
321 26.305 101000001
320 26.315 101000000
319 26.325 100111111
318 26.335 100111110
317 26.345 100111101
316 26.355 100111100
315 26.365 100111011
314 26.375 100111010
313 26.385 100111001
312 26.395 100111000
311 26.405 100110111
310 26.415 100110110
309 26.425 100110101
308 26.435 100110100
307 26.445 100110011
306 26.455 100110010
305 26.465 100110001
304 26.475 100110000
303 26.485 100101111
302 26.495 100101110
301 26.505 100101101
300 26.515 100101100
299 26.525 100101011
298 26.535 100101010
297 26.545 100101001
296 26.555 100101000
295 26.565 100100111
294 26.575 100100110
293 26.585 100100101
292 26.595 100100100
291 26.605 100100011
290 26.615 100100010
289 26.625 100100001
288 26.635 100100000
287 26.645 100011111
286 26.655 100011110
285 26.665 100011101
284 26.675 100011100
283 26.685 100011011
282 26.695 100011010
281 26.705 100011001
280 26.715 100011000
279 26.725 100010111
278 26.735 100010110
277 26.745 100010101
276 26.755 100010100
275 26.765 100010011
274 26.775 100010010
273 26.785 100010001
272 26.795 100010000
271 26.805 100001111
270 26.815 100001110
269 26.825 100001101
268 26.835 100001100
267 26.845 100001011
266 26.855 100001010
265 26.865 100001001
264 26.875 100001000
263 26.885 100000111
262 26.895 100000110
261 26.905 100000101
260 26.915 100000100
259 26.925 100000011
258 26.935 100000010
257 26.945 100000001
256 26.955 100000000
255 26.965 011111111
254 26.975 011111110
253 26.985 011111101
252 26.995 011111100
251 27.005 011111011
250 27.015 011111010
249 27.025 011111001
248 27.035 011111000
247 27.045 011110111
246 27.055 011110110
245 27.065 011110101
244 27.075 011110100
243 27.085 011110011
242 27.095 011110010
241 27.105 011110001
240 27.115 011110000
239 27.125 011101111
238 27.135 011101110
237 27.145 011101101
236 27.155 011101100
235 27.165 011101011
234 27.175 011101010
233 27.185 011101001
232 27.195 011101000
231 27.205 011100111
230 27.215 011100110
229 27.225 011100101
228 27.235 011100100
227 27.245 011100011
226 27.255 011100010
225 27.265 011100001
224 27.275 011100000
223 27.285 011011111
222 27.295 011011110
221 27.305 011011101
220 27.315 011011100
219 27.325 011011011
218 27.335 011011010
217 27.345 011011001
216 27.355 011011000
215 27.365 011010111
214 27.375 011010110
213 27.385 011010101
212 27.395 011010100
211 27.405 011010011
210 27.415 011010010
209 27.425 011010001
208 27.435 011010000
207 27.445 011001111
206 27.455 011001110
205 27.465 011001101
204 27.475 011001100
203 27.485 011001011
202 27.495 011001010
201 27.505 011001001
200 27.515 011001000
199 27.525 011000111
198 27.535 011000110
197 27.545 011000101
196 27.555 011000100
195 27.565 011000011
194 27.575 011000010
193 27.585 011000001
192 27.595 011000000
191 27.605 010111111
190 27.615 010111110
189 27.625 010111101
188 27.635 010111100
187 27.645 010111011
186 27.655 010111010
185 27.665 010111001
184 27.675 010111000
183 27.685 010110111
182 27.695 010110110
181 27.705 010110101
180 27.715 010110100
179 27.725 010110011
178 27.735 010110010
177 27.745 010110001
176 27.755 010110000
175 27.765 010101111
174 27.775 010101110
173 27.785 010101101
172 27.795 010101100
171 27.805 010101011
170 27.815 010101010
169 27.825 010101001
168 27.835 010101000
167 27.845 010100111
166 27.855 010100110
165 27.865 010100101
164 27.875 010100100
163 27.885 010100011
162 27.895 010100010
161 27.905 010100001
160 27.915 010100000
159 27.925 010011111
158 27.935 010011110
157 27.945 010011101
156 27.955 010011100
155 27.965 010011011
154 27.975 010011010
153 27.985 010011001
152 27.995 010011000
151 28.005 010010111
150 28.015 010010110
149 28.025 010010101
148 28.035 010010100
147 28.045 010010011
146 28.055 010010010
145 28.065 010010001
144 28.075 010010000
143 28.085 010001111
142 28.095 010001110
141 28.105 010001101
140 28.115 010001100
139 28.125 010001011
138 28.135 010001010
137 28.145 010001001
136 28.155 010001000
135 28.165 010000111
134 28.175 010000110
133 28.185 010000101
132 28.195 010000100
131 28.205 010000011
130 28.215 010000010
129 28.225 010000001
128 28.235 010000000
127 28.245 001111111
126 28.255 001111110
125 28.265 001111101
124 28.275 001111100
123 28.285 001111011
122 28.295 001111010
121 28.305 001111001
120 28.315 001111000
119 28.325 001110111
118 28.335 001110110
117 28.345 001110101
116 28.355 001110100
115 28.365 001110011
114 28.375 001110010
113 28.385 001110001
112 28.395 001110000
111 28.405 001101111
110 28.415 001101110
109 28.425 001101101
108 28.435 001101100
107 28.445 001101011
106 28.455 001101010
105 28.465 001101001
104 28.475 001101000
103 28.485 001100111
102 28.495 001100110
101 28.505 001100101
100 28.515 001100100
99 28.525 001100011
98 28.535 001100010
97 28.545 001100001
96 28.555 001100000
95 28.565 001011111
94 28.575 001011110
93 28.585 001011101
92 28.595 001011100
91 28.605 001011011
90 28.615 001011010
89 28.625 001011001
88 28.635 001011000
87 28.645 001010111
86 28.655 001010110
85 28.665 001010101
84 28.675 001010100
83 28.685 001010011
82 28.695 001010010
81 28.705 001010001
80 28.715 001010000
79 28.725 001001111
78 28.735 001001110
77 28.745 001001101
76 28.755 001001100
75 28.765 001001011
74 28.775 001001010
73 28.785 001001001
72 28.795 001001000
71 28.805 001000111
70 28.815 001000110
69 28.825 001000101
68 28.835 001000100
67 28.845 001000011
66 28.855 001000010
65 28.865 001000001
64 28.875 001000000
63 28.885 000111111
62 28.895 000111110
61 28.905 000111101
60 28.915 000111100
59 28.925 000111011
58 28.935 000111010
57 28.945 000111001
56 28.955 000111000
55 28.965 000110111
54 28.975 000110110
53 28.985 000110101
52 28.995 000110100
51 29.005 000110011
50 29.015 000110010
49 29.025 000110001
48 29.035 000110000
47 29.045 000101111
46 29.055 000101110
45 29.065 000101101
44 29.075 000101100
43 29.085 000101011
42 29.095 000101010
41 29.105 000101001
40 29.115 000101000
39 29.125 000100111
38 29.135 000100110
37 29.145 000100101
36 29.155 000100100
35 29.165 000100011
34 29.175 000100010
33 29.185 000100001
32 29.195 000100000
31 29.205 000011111
30 29.215 000011110
29 29.225 000011101
28 29.235 000011100
27 29.245 000011011
26 29.255 000011010
25 29.265 000011001
24 29.275 000011000
23 29.285 000010111
22 29.295 000010110
21 29.305 000010101
20 29.315 000010100
19 29.325 000010011
18 29.335 000010010
17 29.345 000010001
16 29.355 000010000
15 29.365 000001111
14 29.375 000001110
13 29.385 000001101
12 29.395 000001100
11 29.405 000001011
10 29.415 000001010
9 29.425 000001001
8 29.435 000001000
7 29.445 000000111
6 29.455 000000110
5 29.465 000000101
4 29.475 000000100
3 29.485 000000011
2 29.495 000000010
1 29.505 000000001
0 29.515 000000000
------------------------------------
pll02a pins 789abcdef
====================================

Midland 79-892

[Sandbagger]

Boy you must have been bored one night to go through all that trouble. And your observations are correct. The information on the web is wrong for the SSB PLL02A chassis. Back in the late 70's, I picked up a Lafayette Telsat SSB-80 mobile, which is the same chassis. Being a young experimenter, I dug into that radio and did more mods than I'd admit to in mixed company. One of the biggest roadblocks in broadbanding that chassis is the VCO block. It's an epoxy sealed unit in a rectangular metal can. You can adjust it for any segment of about 120 channels. Of course, I wanted more then, so I dissected the metal can and chipped away at the bottom layer of epoxy until I exposed the pins for the varacter VCO diode. I then tacked another varactor in parallel with it, which effectively close to doubled my VCO tuning range. But the roadblocks didn't end there. You are still limited by the "Q"of the tuned circuits in the TX and RX strips. I changed cap values between the cans and managed to get a usable range of 26.0 to 28.0.

I never had the radio working at the extreme ends of the PLL's range. I read somewhere that even though the PLL is capable of 511 "channels", the VCO will not lock through them all even if you tune it. There are some other limitations supposedly, but that was years ago, and my recollection has gotten foggy.

Back in those days, a range like that in a CB radio was virtually unheard of. Exports were still 2 or 3 years off. But when I got my TRC-458 with the 858 chip, I found that radio would go even farther with fewer mods. It was a back and forth battle between the local PLL jockeys over which chip, the 02A or the 858, was really the king of range. The 02a had a greater /N count, but the 858 chassis could actually use more of what it had.

I remember making up truth charts for all the PLL's I messed with before I actually committed them to memory (most of which has faded). Ah the good ol days..........

This memory lane flashback was brought to you by Classic Radio Roundup, on 27.115 on your AM dial...... ;D

[Night Ranger]

Mar 20, 2009 22:07:41 GMT -5 Sandbagger said:

Boy you must have been bored one night to go through all that trouble. And your observations are correct. The information on the web is wrong for the SSB PLL02A chassis. Back in the late 70's, I picked up a Lafayette Telsat SSB-80 mobile, which is the same chassis. Being a young experimenter, I dug into that radio and did more mods than I'd admit to in mixed company. One of the biggest roadblocks in broadbanding that chassis is the VCO block. It's an epoxy sealed unit in a rectangular metal can. You can adjust it for any segment of about 120 channels. Of course, I wanted more then, so I dissected the metal can and chipped away at the bottom layer of epoxy until I exposed the pins for the varacter VCO diode. I then tacked another varactor in parallel with it, which effectively close to doubled my VCO tuning range. But the roadblocks didn't end there. You are still limited by the "Q"of the tuned circuits in the TX and RX strips. I changed cap values between the cans and managed to get a usable range of 26.0 to 28.0.

I never had the radio working at the extreme ends of the PLL's range. I read somewhere that even though the PLL is capable of 511 "channels", the VCO will not lock through them all even if you tune it. There are some other limitations supposedly, but that was years ago, and my recollection has gotten foggy.

Back in those days, a range like that in a CB radio was virtually unheard of. Exports were still 2 or 3 years off. But when I got my TRC-458 with the 858 chip, I found that radio would go even farther with fewer mods. It was a back and forth battle between the local PLL jockeys over which chip, the 02A or the 858, was really the king of range. The 02a had a greater /N count, but the 858 chassis could actually use more of what it had.

I remember making up truth charts for all the PLL's I messed with before I actually committed them to memory (most of which has faded). Ah the good ol days..........

This memory lane flashback was brought to you by Classic Radio Roundup, on 27.115 on your AM dial...... ;D

Actually once I figured out the pll02a chip I spent most of my time programming a little Linux bash shell script to calculate all the binary codes and frequencies for me.

Below is the Linux shell script. You can run it several ways;

Show all binary codes;
./midland-79-892-pll02a-truth-chart

Show the binary codes for a single frequency;
./midland-79-892-pll02a-truth-chart 27.115

Show all US 40 CB channels including the RC channels;
./midland-79-892-pll02a-truth-chart cb

Print a small help screen with a list of possible command line parameters.
./midland-79-892-pll02a-truth-chart -h

Save the Linux script as "midland-79-892-pll02a-truth-chart".

Next issue the command below to make the script executable.

chmod u+x midland-79-892-pll02a-truth-chart

and then run it as listed above.

The first run takes the longest as it builds a little database with all the codes. Subsequent runs will run much faster as it just searches the little text database.

# Begin midland-79-892-pll02a-truth-chart script
###############################
#!/bin/bash
# Programmed by Night Ranger

cd $HOME

if [ "$1" = "-h" ]
then
echo ""
echo "================================================"
echo "Display truth chart for pll02a chip installed in a Midland 79-892 AM/SSB CB Radio"
echo "================================================"
echo "midland-79-892-pll02a-truth-chart <= Displays full truth chart for pll02a"
echo "midland-79-892-pll02a-truth-chart cb <= Displays all USA CB and RC channels"
echo "midland-79-892-pll02a-truth-chart 27.115 <= Displays truth chart just for 27.115 (ch 13)"
echo ""
echo "The first time the program is run will take the longest. The program calculates all"
echo "the possible binary combinations for the pll02a in a Midland 79-892 and stores the"
echo "results in a text file located at $HOME/.pll02a-truth-chart. All subsequent runs"
echo "simply search or display the text database."
echo "================================================"
echo ""
exit
fi


if [ ! -e $HOME/.pll02a-truth-chart ]
then
echo ""
echo "================================================"
echo "Calculating all possible pll02a codes for a Midland 79-892. Please wait..."
echo "Subsequent runs will be faster as the results are saved in a local database."
echo "================================================"
echo ""
FREQUENCY=24.395

for CODE in $(seq 511 -1 0)
do
FREQUENCY=`echo "$FREQUENCY + 0.01" | bc`
BINARY=`echo "ibase=10; obase=2; $CODE" | bc`
printf "%3d\t%2.3f\t%09d\n" "$CODE" "$FREQUENCY" "$BINARY" >> $HOME/.pll02a-truth-chart
done
fi

echo ""
echo "===================================="
echo "PLL02a chip codes for Midland 79-892"
echo "===================================="
printf "CODE\tFREQ\tBINARY\n"
printf "pll02a\tpins\t789abcdef\n"
echo "------------------------------------"


# CB plus RC channels

if [ "$1" = "cb" ]
then
FREQUENCY=26.955
CHANNEL=0
for CODE in $(seq 255 -1 211)
do
FREQUENCY=`echo "$FREQUENCY + 0.01" | bc`
BINARY=`echo "ibase=10; obase=2; $CODE" | bc`
#CHANNEL=`echo $CHANNEL + 1 | bc`
printf "%3d\t%2.3f\t%09d\n" "$CODE" "$FREQUENCY" "$BINARY"
done
echo "------------------------------------"
printf "pll02a\tpins\t789abcdef\n"
echo "===================================="
echo ""
exit
fi



if [ -z $1 ]
then
cat $HOME/.pll02a-truth-chart
else
egrep $1 $HOME/.pll02a-truth-chart
fi


echo "------------------------------------"
printf "pll02a\tpins\t789abcdef\n"
echo "===================================="
echo ""
###############################
# End script

: )

Night Ranger

[Night Ranger]

P.S. Below are pictures of a brand new in the box 1977 Midland 79-892 I purchased off of Ebay awhile back. Sweet!

These are pictures of the box being opened for the first time since it left the factory back in the late 1970s!

[mrgumby OT21]

I run one of those radios as a matter of fact I think I talked to you on it one night when you were trying to make on crr when the dx was running.. last year I think it was..I also have an RCA co-pilot that has the same board in it as well...I like the receive on those radios in the base they are pretty quiet on the floor noise..I saw those new in the box on ebay there was one seller that had a couple of them...seems they pop on there still once in a while

[Sandbagger]

Mar 21, 2009 8:47:31 GMT -5 Night Ranger said:

P.S. Below are pictures of a brand new in the box 1977 Midland 79-892 I purchased off of Ebay awhile back. Sweet!

These are pictures of the box being opened for the first time since it left the factory back in the late 1970s!

That's sweet. Getting a never opened brand new 30 year old radio. I'd love to find a vintage radio like that. It would be too much to ask for a Browning or Tram like that, but I'd even be happy with a Midland, SBE, Royce or Cobra, or any of the more popular rigs....

[Sandbagger]

Mar 20, 2009 22:30:03 GMT -5 Night Ranger said:

Mar 20, 2009 22:07:41 GMT -5 Sandbagger said:

Boy you must have been bored one night to go through all that trouble. And your observations are correct. The information on the web is wrong for the SSB PLL02A chassis. Back in the late 70's, I picked up a Lafayette Telsat SSB-80 mobile, which is the same chassis. Being a young experimenter, I dug into that radio and did more mods than I'd admit to in mixed company. One of the biggest roadblocks in broadbanding that chassis is the VCO block. It's an epoxy sealed unit in a rectangular metal can. You can adjust it for any segment of about 120 channels. Of course, I wanted more then, so I dissected the metal can and chipped away at the bottom layer of epoxy until I exposed the pins for the varacter VCO diode. I then tacked another varactor in parallel with it, which effectively close to doubled my VCO tuning range. But the roadblocks didn't end there. You are still limited by the "Q"of the tuned circuits in the TX and RX strips. I changed cap values between the cans and managed to get a usable range of 26.0 to 28.0.

I never had the radio working at the extreme ends of the PLL's range. I read somewhere that even though the PLL is capable of 511 "channels", the VCO will not lock through them all even if you tune it. There are some other limitations supposedly, but that was years ago, and my recollection has gotten foggy.

Back in those days, a range like that in a CB radio was virtually unheard of. Exports were still 2 or 3 years off. But when I got my TRC-458 with the 858 chip, I found that radio would go even farther with fewer mods. It was a back and forth battle between the local PLL jockeys over which chip, the 02A or the 858, was really the king of range. The 02a had a greater /N count, but the 858 chassis could actually use more of what it had.

I remember making up truth charts for all the PLL's I messed with before I actually committed them to memory (most of which has faded). Ah the good ol days..........

This memory lane flashback was brought to you by Classic Radio Roundup, on 27.115 on your AM dial...... ;D

Actually once I figured out the pll02a chip I spent most of my time programming a little Linux bash shell script to calculate all the binary codes and frequencies for me.

Below is the Linux shell script. You can run it several ways;

Show all binary codes;
./midland-79-892-pll02a-truth-chart

Show the binary codes for a single frequency;
./midland-79-892-pll02a-truth-chart 27.115

Show all US 40 CB channels including the RC channels;
./midland-79-892-pll02a-truth-chart cb


Save the Linux script as "midland-79-892-pll02a-truth-chart".

Next issue the command below to make the script executable.

chmod u+x midland-79-892-pll02a-truth-chart

and then run it as listed above.

The first run takes the longest as it builds a little database with all the codes. Subsequent runs will run much faster as it just searches the little text database.

# Begin midland-79-892-pll02a-truth-chart script
######################################
#!/bin/bash
# Programmed by Night Ranger

cd $HOME

echo ""
echo "===================================="
echo "PLL02a chip codes for Midland 79-892"
echo "===================================="
printf "CODE\tFREQ\tBINARY\n"
printf "pll02a\tpins\t789abcdef\n"
echo "------------------------------------"


if [ ! -e $HOME/.pll02a-truth-chart ]
then
FREQUENCY=24.395

for CODE in $(seq 511 -1 0)
do
FREQUENCY=`echo "$FREQUENCY + 0.01" | bc`
BINARY=`echo "ibase=10; obase=2; $CODE" | bc`
printf "%3d\t%2.3f\t%09d\n" "$CODE" "$FREQUENCY" "$BINARY" >> $HOME/.pll02a-truth-chart
done
fi

# CB plus RC channels

if [ "$1" = "cb" ]
then
FREQUENCY=26.955
CHANNEL=0
for CODE in $(seq 255 -1 211)
do
FREQUENCY=`echo "$FREQUENCY + 0.01" | bc`
BINARY=`echo "ibase=10; obase=2; $CODE" | bc`
#CHANNEL=`echo $CHANNEL + 1 | bc`
printf "%3d\t%2.3f\t%09d\n" "$CODE" "$FREQUENCY" "$BINARY"
done
echo "------------------------------------"
printf "pll02a\tpins\t789abcdef\n"
echo "===================================="
echo ""
exit
fi



if [ -z $1 ]
then
cat $HOME/.pll02a-truth-chart
else
egrep $1 $HOME/.pll02a-truth-chart
fi


echo "------------------------------------"
printf "pll02a\tpins\t789abcdef\n"
echo "===================================="
echo ""

#############################
# End script

: )

Night Ranger

That's pretty cool. Now if I only had a computer with Linux on it....... Doh!