IMD Meter


IMD Meter PCB Assembly

Assembled IMD Meter in Deluxe Enclosure with Engraved Front Panel


IMD Meter - Description - The IMD Meter is a stand alone instrument designed to display your IMD while you are transmitting PSK.  No connection to your rig is required, nor is a connection to your PC needed. 


The RF signal is picked up by a short whip antenna on the meter, fed into an AGC controlled RF amplifier, the signal is detected, sampled with an A/D converter under the control of a micro controller.  The signal is analyzed by firmware on the micro controller and the equivalent IMD is calculated and displayed on a 3 digit LED array built into the IMD Meter.  The AGC RF front end has a wide dynamic range and adapts to power output from QRP to QRO.  Level setting is under the manual control of the operator, who can choose the output drive level consistent with a clean signal.


Kit - The IMD Meter is designed as an easy to build kit project.  It is fabricated on one high quality 4 layer PC Board using leaded resistors, capacitors, semi-conductors and inductors to simplify kit assembly.  Integrated circuits are socketed DIP.   No Surface Mount Devices (SMD) are used.  The enclosure is an Eagle Plastics chassis.  The front panel is engraved, with panel holes cut by an NC machine.  The kit also includes a 12.5 VDC power supply. 


Fully Assembled Meter - If building kits is not your thing, the IMD Meter is available fully assembled.  This ready to go unit includes the assembled & tested PCB, antenna, new Deluxe Enclosure, and a 12.5VDC power supply. 


IMD Meter Project Status- The IMD Meter was introduced at SEAPAC in June of 2004.  The product has now been in full production since July, 2004.  See IMD Pricing and Ordering for further information.


IMD Meter Compared to the PSK Meter Product

Another BPSK signal analyzer, the PSK Meter,  designed by George Rothbart,  KF6VSG, was introduced in 2003 and is similar in function to the IMD Meter.  Further information about this product is available on website  The difference between these products is this: 

The PSK Meter is connected to the transceiver output with a coax TEE connector, feeding RF to the PSK Meter hardware.  The IMD Meter picks the signal off the air with a short whip antenna and runs it through a wide band, AGC RF amplifier.

The PSK Meter detects the signal, samples it with an A/D converter, analyzes the wave form and transmits it to the PC via a serial port or a USB/Serial adapter for further analysis and display.  The IMD Meter controls the AGC of its RF front end, detects the signal, analyzes the wave form, calculates the IMD and displays it on a 3 digit LED array built into the meter.  No connection to the PC is required.

The PSK Meter software that runs on the PC controls the PC WAVE audio drive level to optimize the maximum level that will produce a clean signal.  This software runs in the back ground to adjust the output when necessary.  The IMD Meter provides the information to the operator from its 3 digit LED display, the operator manually adjusts the audio drive level to produce the desired power output, consistent with a clean IMD.

The PSK Meter requires a jumper change to move from QRP to Low Power operation.  The IMD Meter, handles QRP to QRO automatically.

Both products work on BPSK and QPSK 31 and 63 signals.

Click IMD Meter - Brochure for a one page copy of the IMD Meter brochure.

IMD Meter - Manuals  Full documentation for the IMD Meter kit is available for your review.  These documents are in .pdf format.  Current copies of the IMD Meter Construction Manual and IMD Meter Operating Manual are found in the IMD Meter Manuals section.

Inquirys and Questions - see Contact Us