Weekend Project
30 Meter BJT QRP Transceiver Rolf Heine, DL6ZB
On a rainy Saturday
afternoon, I searched through my collection of spare parts for a
suitable connector to fabricate a cable. During this pursuit, I
stumbled upon a small bag containing 10111 kHz crystals.
Inspired by the discovery, I decided to harness the potential of these
crystals by conceptualizing a minimized QRP transceiver tailored for
the 30-meter band.
The result is a dedicated 30-meter single-band transceiver boasting an
RF output of approximately 1.5 watts, covering a tuning range from
approximately 10108 to 10122 kHz.
The primary design objective was to make a QSK transceiver employing
just 5 BJTs and a custom-built diode ring mixer. This TRX provides a
frequency range of at least 10 kHz by adjusting the oscillator
crystals, employing a direct conversion receiver configuration.
All utilized are standard and readily available, with the exception of
the crystals, sourced from miscellaneous parts. The depicted version
features an IE-500 diode ring mixer.
This transceiver incorporates two oscillators. One for receiving and
another for transmitting which permits frequency offsetting of the
transmitter frequency. This results in a transmit frequency shift
during transmission, thereby generating a sidetone in the receiver
section. The high isolation of the RX/TX antenna relay ensures a
satisfactory level of AF sidetone.
The AF amplifier necessitates a high-impedance load at the output;
hence, 2000 Ohm headphones were used. Anti-parallel germanium diodes at
the AF output are a good choice for limiting the audio frequency to a
comfortable level when encountering strong signals at the antenna input.
An alternative version integrates an additional AF filter exhibiting a
frequency peak of around 700 Hz. Notably, the 4700 uH inductors
employed are FASTRON 07P-472J-51.
A Zener diode ZD33 is positioned at the collector of the output BJT
2N3553 to safeguard against potential damage to the output transistor
if there's an antenna mismatch or sudden antenna disconnection during
transmission. This protective measure prevents immediate damage to the
output transistor in the absence of a load during transmission.
While the 2N3553 transistor may pose procurement challenges, any other
low-power RF transistor rated at 2 watts, such as 2N3866 or even a
BD135, can serve as a substitute. BS170 FETs may be worth a try.
The enclosure utilized originates from Otto Schubert GmbH, Germany, Case No. 6, measuring 111 x 55 x 30 mm (L x W x H).
