Weekend Project
30 Meter BJT QRP Transceiver
Rolf Heine, DL6ZB

This is one more weekender. It's a 30 meter transceiver with an RF output of about 1.5 watts.
Use of other frequencies is possible by changing crystals and RF filters.

The design goal was to make a QSK transceiver with only 5 BJTs and a diode ring mixer.
This TRX offer a frequency coverage of at least 10 kHz by pulling the oscillators crystals.
The receiver is of DC type. C trimmers 50 pF are used to pull the crystals a few kHz.
The tuning range is from about 10108 to 10122 kHz when 10111 kHz are used.

There are 10116 kHz QRP frequency crystals available from serveral ham radio suppliers for a few bucks.

No special parts are used except the crystals. It's all from the junk box. The version from the pictures has a IE-500 diode ring mixer.
However, in another version, the 1N4148 diode ring mixer shown in the schematic here works great, too.

This transceiver has 2 oscillators, one for the RX and one for TX. This allows easy offsetting the transmitter and a sidetone.

The headphone is of high impedance type. I used 2000 ohms types. Low impedance headphones will require an additional AF stage.
The anti-parallel Germanium diodes at the AF output are necessary to limit the AF to a comfortable audio level.

Another version has an additional AF filter for better audio with a center frequency of approx. 700 Hz installed.
The 4700 uH inductors are FASTRON 07P-472J-51. These are available from many suppliers worldwide.

There's a Zener diode ZD33 at the collector of the output BJT 2N3553.
That diode is essential
to prevent serious damage to the output transistor if the antenna is mismatched or disconnected when the transmitter is keyed.

The 2N3553 may be hard to find. Any other RF 2 watt low power 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

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