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.
