S E Reset Dash Memory



Fig 2—Schematic for the MPC CW keyer application. MPC application interconnections are listed alphabetically. See text.

C27, C28—0.001-fiF disc ceramic. Q1— 2N2222A. U13—74LS109 dual J-K flip-flop.

C29—0.01-/iF disc ceramic. R12, R13, R15—10 kO, V* W. U14—74LS244 3-state, octal buffer/line driver.

8 sex character was input during the slot, a space would be entered into the ASCII string. A specific keystroke on the keypad signals the end of the message.

Application No. 2—the MPC-RCU

With the addition of the circuitry in Fig 3, the MPC can be used as a remote control unit (RCU) for a Kenwood TS-440S MF/HF transceiver (equipped with Kenwood's IC-10 option) for mobile operations. Borrowing an idea from a commercial VHF/UHF system, the transceiver is locked in the car trunk with the MPC/RCU installed under the dash. Frequency and mode are entered via the keypad, as are frequency storage and recall operations involving the MPC/RCU EEPROM. Transceiver frequency changes can be performed in two ways: (1) The up/dn switch on the rig's standard mobile mic and (2) with an A/D converter (ADCQ809) reading the position of a potentiometer (R3, freq). In the A/d method, the MPC converts the position of the potentiometer into serial frequency commands and sends them to the TS-440S at 4800 bit/s. I find that the A/d method allows a faster tuning rate than the rate used with the microphone up/dn switch. It closely emulates the speed of the TS-440's tuning dial. The A/d method is also a less expensive alternative to using a rotary position encoder.

Also shown in Fig 3 is a method of expanding the I/O of the

MPC by using spare ADC0809 inputs. Switch position (S2—rit/on) is determined by doing an A/D conversion. The printer output pin of the 8052AH-BASIC is used to drive the optoisolator interface to the radio. Commands are output with the BASIC-52 PRINT* statement. The PWM pulse sequence output of the 8052AH provides the correct number of clock pulses to the A/D converter to eliminate polling for end-of-conversion.

The RCU made mobile operation possible for me. All TS-440S functions cannot be remotely controlled, however. The rig is broadband enough not to require remote control of its antenna tuner, but the lack of ALC and S-meter information in the TS-440S serial data stream, along with the inability to use some of the TS-440S operating features like notch, IF shift and speech processing, are drawbacks that should be considered before building the RCU.

In order to get a reasonable radio tuning range from the 8-bit A/D converter, the program I use gives a tuning resolution of 100 Hz when tuning with the potentiometer. Fine tuning with 10-Hz resolution is still available when using the up/dn switches on the TS-440S microphone. Whatever the solution, it should not involve a rotary switch with discrete mechanical "clicks" or detents.

(continued on page 15)



Fig 3—Schematic for the TS-440S RCU (remote control unit). MPC application interconnections are listed alphabetically. See text.

C21, C22—470-pF disc ceramic. C23, C26—O.QI-fiF disc ceramic. C24, C25—0.001-fiF disc ceramic. DS2—red LED. LS1—8-0 speaker. Q2—2N2222A.

R3— 10-kfi 10-turn potentiometer (Precision

Bourns 3540S-1-103). R8—1.8 kO. 1/4 W. R10—8.2 kO, Va W. R11—1-kii potentiometer, audio taper.

S2—SPST miniature toggle switch.

U15—ADC0809 8-bit A/D converter with

8-channel multiplexer. U16—MCT4 General Instruments optoisolator. U17—NTE3042 Sylvania optoisolator.

A Logarithmic RF Detector for Filter Tuning

By Zack Lau, KH6CP ARRL Lab Engineer

Did you ever shy away from building bandpass filters because you don't have a spectrum analyzer and tracking generator to tune up the filters? The advantage of being able to use a spectrum analyzer for filter tuning Is the terrific dynamic range it offers: 60 dB or more. With that sort of dynamic range, you can usually tell whether a resonator is too high or low in frequency, even if the resonance is far from the design frequency. Commercially available spectrum analyzers are expensive, and building even a cheap spectrum analyzer involves a lot of time and effort.

Another Way

For those of you who don't have access to a spectrum analyzer and don't want to build one, here's an inexpensive alternative that I've devised and use for filter tuning. The logarithmic detector circuit shown in Fig 1 provides over 60 dB of

dynamic range. (The MC3356 and similar ICs have been used as part of inexpensive spectrum analyzers.) Fortunately, this IC has enough frequency response to work well even at 10 meters.

Ideally, you'd use a sweep generator

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    What does the string schematic look like for an Remote Control car?
    8 years ago

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