The Heathkit Deviation Meter

Have you ever had someone tell you that you were over-modulating on your two-meter FM rig? One solution to oven modulation is the new Heath-kitâ„¢ Deviation Meter Kit (IM-4180) from the Heath Company. This deviation meter can be a useful addition for anyone who operates FM equipment. At a cost of $149.95 it is not for everyone, but it will permit more amateurs to check their equipment's deviation levels accurately.

Construction

The kit can be constructed in two or three nights. Only two printed circuit boards are used, a main circuit board and a converter one. Ail components {except the front-pane! controls, the front-panel jacks, and the meter itself) are mounted on these two circuit boards. The front pushbutton switch assembly solders directly to the circuit board and simplifies assembly. I he kit uses eight integrated circuits which are mounted using IC sockets. Six of these are RCA COSMOS operational amplifiers which help minimize current drain but require cautious handling.

The main circuit board holds alJ of the circuitry except for the converter circuitry and the front-panel mounted items. The converter circuitry is mounted on a separate circuit board which is mounted in a shielded enclosure on the rear of the front paneL

Calibration rhe alignment and calibration requires only one piece of external equipment. The deviation meter's local oscillator can be aligned using a frequency counter or a standard FM broadcast receiver. The frontpanel meter is used for alignment and calibration meteringOperation

The deviation meter requires ten AA cells for operation. The manual indicates an operating life of about eighty hours for either zinc-carbon or alkaline cells. A battery charger/ eliminator for use with nickel cadmium batteries is an optional accessory. Battery voltage can be checked by the use of the front-panel BATT pushbutton.

A tune switch allows you to peak the meter indication using the main- and fine-tuning controls. The fine-tuning control is a potentiometer which controls a varactor diode in the local oscillator. The fine-tuning control simplifies tuning at VHF and UHF frequencies. Operation from 25 to 50 MHz uses the Jocai oscillator fundamental output, but operation from 50 to 1000 MHz uses the local oscillator harmonic outputs. A dualgate MOSFET is used as a variable frequency oscitlator. This is a diode-protected device, and while no precautions are given in the manual, I advise caution when installing this transistor, since the one I installed faited to operate. A replacement was installed with no problem. A hot-carrier diode is used as a frequency-converting mixer. An i-f gain control is provided on the front panel to control sensitivity. Between 50 and 500 MHz, the deviation meter has a minimum sensitivity of 35 mV. Accuracy (full scale) is specified as plus or minus three percent.

Meter ranges of 0-2, 0 7.5, 0>20h and 0-75 kHz peak are selected by front-panel pushbuttons. The 0-7,5-kHi range is useful for setting the FM deviation of amateur equipment. The

0-2-kHz range uses a low-pass filter and is most useful for adjusting continuous tonecoded squeich systems, The deviation meter uses a pulse-counting detector operating at a 200-KHz

A speaker output jack is provided for an external speaker (no internal speaker is pro vided). The audio amplifier provides 100 mW minimum into an 8-Ohm speaker A front-panel switch selects a de-emphasis of 750 us for two-way rad<o, or 75 us for standard FM broadcast. This de-emphasis switch affects only the speaker output.

A scope output is provided on the front panel. This output provides a nominal 13-mV/kHz peak superimposed on a dc voltage of about 2.7 volts. This output permits you to monitor the input for clipping which would not be apparent from the meter reading.

Conclusion

I enjoyed constructing my Heathkit deviation meter and find il simple tooperate, Its portability makes it ideal for checking the local repeater or your friends" equipment 1 particularly like the ease with which subaudible tone levels can be checked. Heath Com pany, Benton Harbor Ml 49022. Reader Service number H5.

Bruce A. Beyerlein WB9WFH

Waukesha Wl

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  • carita enestam
    HOW TO USE HEATHKIT IM4180 FREQUECNY DEVIATION METER?
    2 years ago

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