Theory of Operation: The transmitted RF signal output from your antenna is picked
up by the telescoping antenna on the meter and fed into an AGC controlled wide band RF amplifier.  The RF wave form of the signal is diode detected, then sampled with an A/D converter under control of an on-board micro controller.  The shape of the wave form is then analyzed by the micro controller's firmware, the signal is calculated and the IMD is displayed on the meter 3 digit LED readout.

The signal quality is measured by analyzing the shape of the wave form which allows for precise IMD readings to be produced in real time while transmitting both in idle mode and even as you are transmitting text.  It also adjusts to your transmitted signal levels automatically and handles QRP to QRO RF output.  There are no levels to set or knobs to twist here.  Just turn it on and it analyzes and displays automatically.  

The IMD Meter also doubles as a relative HF Field Strength Meter and calibration is
approximately 1 dB per unit. The complete enclosure sports a very small footprint: 

2.75H x 4.5W x 1.75D (inches) and weighs just 5 ounces. The telescoping antenna extends from 5.5 to 20 inches. 

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Do I use one?   I wouldn't be without it.    I only wish all PSK users had one,  more especially some of our our friends "South of the Border" whose PSK tracks look like Grand Central Station on my waterfall.   This IMD Meter is a precise stand-alone unit
at a reasonable price.  All IMD Meters are assembled, tested and ready to operate.