Look! No Resistors!

Updated June 1, 2013

This was an attempt to see how few parts it takes to make a working receiver. I built it as an entry in the 1999 HamComm regen building contest. It was also a response to a thread on QRP-L about what would be the best frequency range if you had to choose. I chose 5.7 to 7.6 MHz because it included two short-wave broadcast bands and 40m, which I've always thought of as "ham central," at least for CW.

The circuit is slightly wierd in that the 2K ohm headphones are used for two functions. First, they provide a good value of bias resistance for the FET. Headphones were typically made with the DC resistance very close to 2000 ohms. This is a holdover from the wire telegraph days. The 2000 ohms is the bias resistor here, so if you try and build one of these things keep that in mind. Using Walkman-type phones on this rig would be disastrous, for instance. The other function the phones serve is, of course, to get the demodulated audio to your ears. Well, there isn't much of it with this set. You have to be in a quiet room and your ears have to be in good shape. Band noise is audible, but just. I have used this receiver on the air, but it's not easy. It is a lot of fun, though. It doesn't produce as much audio as my first FET regen, which is also just a single FET scheme. That's mostly because of the other set has the audio taken from the drain circuit of the FET, where there is more audio available. You have to use the most sensitive phones you can find for this to work. I use some WW2 R-14's to good effect.

The solid construction really helps. The radio is not completely shielded, and the antenna coupling has to be pretty heavy, so this radio does show hand capacity effects and it overloads pretty easily. To turn the power on and off you just plug in or unplug the headphones. Notice that there is no "grid leak" in this circuit. I couldn't figure out why you needed one, so I left it out. That's two less parts. The receiver will actually work without the phones bypass capacitor, but it does show more hand capacity effect.

The Minimal Receiver

Inside View of the Receiver

Schematic Diagram of the Receiver

Parts List:

C1 50-130pF variable (from WW2 Command receiver)
C2 .01uF 50V mono ceramic
Q1 MPF102
B1 9V
L2 5uH of a Command transmitter tank coil
L3 Rotating link inside L2, 4T
L1 1T link around L2
HS1 2K ohm headphones

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