Weekend Project
30 Meter BJT QRP Transceiver
Rolf Heine, DL6ZB

On a rainy Saturday afternoon, I rummaged in the junkbox for a suitable plug to make a cable. On this occasion, a small bag with 10111 kHz crystals fell into my hands.

These beautiful crystals had to be put to a sensible use. So the idea for a simple QRP transceiver for the 30 metre band was born.

It's a 30 meter single bander with an RF output of about 1.5 watts and a tuning range from about 10108 to 10122 kHz.
Other frequencies can be used by changing the crystals and RF filters.

The design goal was to make a QSK transceiver with only 5 BJTs and a homemade diode ring mixer.
This TRX offers a frequency coverage of at least 10 kHz by pulling the oscillator crystals.
The receiver is a direct conversion.

No special parts are used except the crystals. It's all from the junk box. The version shown in the pictures has an IE-500 diode ring mixer.

This transceiver has 2 oscillators, one for the RX and one for the TX. This allows easy offsetting of the transmitter which shifts off the transmit frequency and as a side effect provides a sidetone because the receiver remains turned on during transmitting. Thanks to the high isolation of the RX/TX antenna relay the AF sidetone level is convinient.

The AF amplifier needs a high impedance load at the output. I used 2000 Ohm headphones. The anti-parallel germanium diodes at the AF output are necessary to limit the AF to a comfortable audio level when strong signals enter the antenna input.

Another version has an additional AF filter with a frequency peak of around 700 Hz.
As an example, the 4700 uH inductors are FASTRON 07P-472J-51.

There's a Zener diode ZD33 at the collector of the output BJT 2N3553.
This diode is essential to prevent serious damage to the output transistor if the antenna is mismatched or disconnected while the transmitter is keyed. The output transistor will be damaged immediately if there's no load while the transmitter is keyed without this important measure.

The 2N3553 can be difficult to find. Any other low power RF 2 watt transistor will work, e.g. 2N3866 or even a BD135.

The housing is from Otto Schubert GmbH, Germany, Case No. 6:    111 x 55 x 30 mm (L x B x H)
More information here:

Click on schematic and pictures for higher resolution.

ABACUS-1 FRONT ABACUS-1 REAR ABACUS-1_case_open_1 ABACUS-1_case_open_2 ABACUS-1_case_open_3
ABACUS-1_case_open_6 open 007
Schematic with AF filter
Schematic without AF Filter
Schematic without AF filter
AF filter installed

<<< back