Midland 13-830 Frequency

Paul t. Schmidt K9PS 3108 Brown Road New Cast it- IS 47362

CB to 10

— part XVIII: several PLL rigs

Who called it 'Ancient Mode?"

Recently, many hams l have been converting CB radios to operation on the 10 meter ham band. With 10-channel CBs being sold now, there are many good used 23-channel units available at very reasonable prices. Some of these units will make very handy 10 meter AM phone transceivers, as they contain excellent AM receiver sections as well as efficient

4-Watt output transmitter sections in a small package ideal for mobiie use. One of these units which may be easily (a few hours of work at most) and cheaply (less than $10 for the conversion and perhaps $40 to $50 for the radio) put on ten meters is the Midland model 13-882 C

Although this article is concerned primarily with the 13-882C, the informa

Pll Meter Band Chn
Photo A. An overall shot ot the rig with the case off,

tion can be applied to the following radios which use the PLL-02A phase-locked^ loop IC in the same circuit configuration: General Motors-CBD-10; Hy-Cain — 2680, 2681, 2683;

Kraco - KCB-2310B,

950, Micro-223A Lafayette - Com-phone

23A, Telsat 1050; Midland-13-830, -857B, -882C, -888B, -955;

Pearce-Simpson—Tiger 23

Truetone —CYJ-4732A-77,

MCC-4434B-67. There are probabiy more units containing the PLL-

02A in the arrangement discussed here. They can be recognized by the numbers PLL-02A on the chip near the front of the rig, three crystals in the radio, and the numbers

PTBM033A0X, PTBMO-

36AOX, PTBMG37AOX, or

PTBM039A0X on the cir cuit board. There are some 40-channel radios using the PLL-02A in a different arrangement (only two crystals) which cannot be put on 10 meters by the method described here, as the crystal that has been eliminated is the crystal to be changed in this modification Also, nt should be noted that earlier versions of the units listed above do not use the same circuitry. The Kraco KCB-233G, for example, uses a crystal synthesizer, and the KCB-2330A uses a PLLOIAchip, which is not equivalent to the PLL-02A chip.

Operation of the PLL02A

The voltage-controlled oscillator (vcol whose frequency is controlled by the PLL-G2A chip and associated circuitry, provides injection to the first receiver mixer and to a transmitter mixer stage. The oscillator operates at 10.695 MHz above the operating frequency, or 37 660 to 37.950 MHz for operation on CB channels 1 to 23.

Output from the vco is also mixed with the third harmonic of the 11.80666 MHz crystal oscillator CQ105) at 35.420 MHz, to produce a difference frequency of 2 24 to 2.53 MHz, which is fed into pin 2 of the PLL chip, 10.240 MHz energy from the 10.240 MHz reference/second receiver mixer injection oscillator is fed into the IC at pin 3.

Inside the IC, the 10.240 MHz signal is divided by 1024 to produce a 10.00 kHz reference signal. The 2.24 to 2.53 MHz signal is divided by nP where n is a number determined by the binary coding from the channel switch to pins 7-15 of the IC. See Table 1.

For channel 1, n is 224, dividing the difference frequency at pin 2 by 224. This frequency is compared to that of the 10.00 kHz reference signal. If the output of the n divider is less t!ian 10.00 kHz, the voltage at pm 5 of the PLL chip (the control voltage for the vco) is raised, causing the frequency of the vco to increase. If, on the other hand, the frequency of the n divider output is higher than 10,00 kHz, indicating that the vco is too high in frequency, the voltage at pin 5 drops, towering the vco's frequency. This action, similar to that of a thermostat, regulates the frequency of the vco. By changing the value of n {the job of the channel switch) or the frequency of the 11 80666 MHz oscillator and adjusting the slug in the vco oscillator coil (to set its tuning range), the operating frequency of the vco, and thereby the operating frequency of the entire rig, can be changed,

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