4 Transistor Super Regen Receiver
This is a pocket sized receiver I built in 1994. The idea
was to make a simple but useable receiver running off 3V. My previous
6 transistor receiver was more bulky, requiring 12V. This meant 10 x AA
cells. I designed and made a PCB, and constructed a small aluminium case
to keep the receiver as comact as possible.
There is nothing unusual with this design. The detector
uses a simple Colpitts oscillator and is of a type commonly used in other
super regen receivers. Of course it is self quenched. Sensitivity with
this type of detector is relatively low, but it's simple and easy to get
working. As always, I provided a regeneration control to set the optimum
operating point; ie. max sensitivity and minimum SCA/stereo subcarrier
The aerial feeds the emitter via a 3.9pF condenser. This sort
of connection causes less tuning drift and loading problems than if fed
directly to the aerial coil. The aerial coil is the usual 4 turns of 18B&S
TCW on an air cored 3/8" former. The 150uH choke is a commercially made
item. In case you notice it, the condenser in series with the tuning condenser
is 43pF. This was 10pF//33pF and was necessary to get the correct tuning
To further simplify this receiver, a volume control was not
fitted. Instead, the regeneration control is used for that function. As
the regeneration is advanced past where the detector just starts oscillating,
gain drops off and so does volume. It is not an ideal method of volume
control, but works to a useable degree.
I used a three transistor amplifier to drive low impedance stereo
headphones. Various condensers are used to filter the quench sufficiently.
Although this audio amp works well, I'm not keen on DC flowing through
the headphones. Again, this was done for simplicity, but if I was to redesign
the circuit again, I would incorporate an output transformer.
The first two transistors provide voltage gain, with the third
being an emitter follower providing current gain and impedance matching
to drive the headphones. Yes, a speaker can be used but the volume isn't
Current consumption at 3V is about 30mA.
Performance isn't bad for what it is, but sensitivity is less than
other receivers. However, at my home 80km from Sydney, all the mainstream
stations are receivable without any problem. Even so, it is not recommended
for DX use. Ideally, the aerial should have been 75cm long, but again,
size considerations meant that a shorter one was used.
email me: cablehack at yahoo