dipmeter

Dip Meter

Building your own Dip Meter is educational and very rewarding.

I built this Dip Meter many years ago. The oscillator is a J-FET with a 2N3904 emitter follower providing RF output for an external frequency counter. The tuning capacitor is a dual section unit of 22 and 34 pf (don't let anyone tell you that you need matched halves on the tuning capacitor...it is not true). Gate current drives the 100 ua meter but is a bit on the weak side. A 50 ua meter would have been better, but this is all I had in the way of a miniature meter (today I would use an amplified LED in place of the meter). Most coils are wound on 1/2 inch or 3/4 inch PVC pipe with banana plugs through the side at each end. The coils are not tapped because the oscillator circuit does not require a tapped coil. The 120 to 180 MHz coil is air-wound #12 house wire soldered to a strip of PCB material with bananna plugs at each end. The 175 to 250 MHz and 225 to 400 MHz coils are just a strip of PCB material with slots cut in it to make up the inductor, and with banana plugs at each end.

No, before you ask, I don't still have not drawn a schematic for this instrument. It was built from scratch-pad drawings and a test-as-you-go design process.

My Dip Meter dial is calibrated in picofarads instead of the usual MHz or KHz markings. I did this because I routinely use this instrument with a digital frequency counter attached to show frequency, and found that the capacitance markings were of more value to me for checking junk-box inductors by connecting them in place of the instrument's regular coils. My Dip Meter coils are also marked with inductance value, which along with the capacitor calibration helps with other circuit design efforts.

This unit has an internal 9 volt battery, and a jack for external power. This lets me use it both on the workbench and as a portable instrument.

The small tuning knob allows fast frequency sweeps, while the larger knob skirt also acts as a knob for slow tuning to exact frequencies.