Single Transistor Receiver - Regen Receiver for the 30m Band
A 10 Parts "DX Receiver"
The next idea after the successful construction of a single transistor transmitter for 30m was to try an simple 30m regen receiver with best possible performance.
This receiver is surprisingly sensitive. It's performance is far better than I had expected. When I connected the receiver to the antenna the first time, I hardly believed what I heared! With just one transistor this little thing was able to hear everything - loud and clear. Listen to an audio file here: audion.mp3
A word about the frequency stability. The receiver frequency depends on all parts of the circuit, even a swinging wire antenna and a matchbox, because all parts affects the Audion frequency. This is a tribute to the extreme simplicity of this kind of receiver. Stability and performance may be significantly increased by using a buffer pre-amplifier at the expense of a more complex circuit. If a pre-amplifier stage is used it is necessary to shield the regen stage from the frontend.
The circuit diagram shows the complete Regenerative Receiver schematic. The tickling capacitor is tuned to about 30pF. The variable resistor R2 is tuned so that the RX draws a current of about 150 µA. A frequency counter for alignment of the circuit is very useful, although a broadband receiver as a helper to find the RX frequency will be fine.
It is very important (!) to use Hi-Z (~2-4 kOhms) headphones, otherwise the circuit won't work. Use a little AF transformer with a suitable Z-ratio if you don't have a Hi-Z headphone. I use very sensitive ancient 4 kOhms headphones which I found on ebay. The variable resistor R2 is a 10 kOhm fixed in version 2.
When using a 9V alkaline battery this tiny receiver will work for up to 3.000 hours (150 µA current). It runs pretty well with a 9V battery. (usual 6LR61 type).
Weekend Project: 30m QRPP
Single Transistor CW Transmitter
Output is approx. 300-400 mW. The 2-crystal version allows increased frequency tuning. See the red lines on the Reverse Beacon Network map at the window below.
Even W3LPL at a distance of 4200.2 mi (6759.6 km) heared the 300 mW signal on 10114.2 kHz from Germany with a signal quality of 7 to 9 dB SNR. This corresponds to a relative distance of 14 mi/mW or 22.5 km/mW !
The decoupling at the collector is essential to prevent tx chirp. This transmitter produces a clean chirp-free signal.
I used a 12 V battery as a power supply and a 2x30m random wire inverted-V up 25m above ground level.
Here are the first 3 QSO's made with the 300 mW QRPP:
30M F5LBG F CW Bernard 579 579 01-Dez-2012 11:27
30M ON4MB ON CW Walter 419 599 01-Dez-2012 14:29
30M OH3HTR OH CW Kari 539 589 01-Dez-2012 15:02