2007-11-04
Regenenerative-Reflexive Receiver
I first saw this detector topology on PA2OHH's website, and then again saw that PY2OHH had a go at it as well. I had to give it a try, it is obviously regenerative, but also appeared to be partially reflexive.
The circuit is simple and was thrown together in only a few minutes on a small piece of PCB. The lash-up included just the detector, using a T68-7 core for the coil and large tuning capacitor. The detected audio was delivered to my old Archer amplified speaker to quickly assess the circuit.
It works very well. The -ve feedback from the collector to the base bias helps control its break into oscillation. Initially I used 100 pF, but I increased this to 1 nF for smoother operation. This also enhances its reflexive properties, giving it quite good audio gain with only one transistor.
There is some distortion inherent in the detector, but its simplicity and stability is a big advantage. It took only minutes to get a working receiver with it, and easily heard the stronger shortwave stations with only two alligator clip leads for the antenna.
Here are some videos of the prototype receiver in operation (excuse the enormous mess my bench is currently in):
- Some Jazz on VOA (2 MiB)
- Tuning Around (4 MiB)
As there is no bandspread capacitance or reduction drive in this initial lash-up; the receiver is very touchy to tune. The full sweep of the cap tunes from about 3.9 MHz to over 18 MHz, far too much bandspread for practical use. This is easily fixed in a more permanent version of the receiver however.
3 comments.
Updates
- 2007-12-18: Receiver Boxed Up
- I put the regen-o-reflexive receiver on 31 metres and put it in a box.