A two band 1 chip + 1 transistor
1 watt QRP CW transceiver
Minimum performance rig for portable
Very simple minimum performance CW rig for portable outdoors activities.
Is this your rig?
If you do like extreme simplicity then you do have the right mentality for this simple rig! Otherwise I would advice you to make a better one and only take a quick look at the pictures and schematic diagram of this simple rig.
Well I hope
that I did not discourage you too much. It is possible to make many QSO's with
this simple rig. It is easy to pack for your hikes and you do not have to worry
about damaging an expensive rig. Take it with you on your holidays to make many
QSO's during camping. But do not expect more than just sufficient
HIS trx during a portable trip in the woods.
And now the serious partVery simple rig for portable use
Just sufficient performance
The whole portable station in a lunchbox, everything fits in it!
This is a real minimum radio amateur technology QRP design, simple and non-professional.
One evening I tried if it is possible to use a C-MOS switch (1/4 of a 74HC4066) as an amplifier, just like a transistor. After a few hour's fight with oscillating circuits, I suddenly found out how to do that. Two capacitors with good RF performance are required for stable operation of the "74HC4066 C-MOS switch transistor". See for details the schematic diagram given below. Of course it is not a perfect amplifier, it is quite noisy, so the sensitivity of the receiver is only 3 uV. That is good enough for 7 MHz and 10 MHz, but not for the higher bands. I wanted to make it really simple, 1 transistor and 1 chip, but not too extreme. The LF output power should be sufficient to give perfect readable signals with a walkman headset. But there is no side tone oscillator and no volume control. The key is a simple pushbutton at the front of the transceiver (see picture).
It is easy to build the transceiver on a small single sided unetched PCB board as you can see on the photographs.
Just two "74HC4066 C-MOS switch transistor".
It looks as if the input resistor of the first stage is missing. But you can find it at the input of the mixer.
If LF oscillation occurs, decrease R1. Select R2 so that in receive mode, the supply voltage of the 74HC4066 is approximately 5 volts.
The VXO is a "C-MOS switch transistor". In transmit mode, extra RF power is needed for the final transistor amplifier. This is obtained by the circuit consisting of the diode 4148 and 330 ohm/100 pF. In transmit mode, the VXO is also tuned a bit lower in frequency due to this circuit. So when you receive a station, the VXO signal should be higher than it's frequency. Here the values of the tuning ranges of my version:
The VXO signal is amplified to 1 watt by a transistor 2N3553.
The 1k ohm resistor makes the amplifier more stable when mismatches occur. The 0.68 uH / 180 pF are tuned to the second harmonic of the 7 MHz transmit signal for extra suppression. One output filter is used for both 7 and 10 MHz.
Built via the ugly method (dead bug method). Parts are soldered at one side of the print.
Inductances are commercially available types looking like big resistors.
Do not use a HCT type but a HC type!
If LF oscillation occurs, decrease R1.
Select the value of R2 so that in receive mode, the supply voltage of the 74HC4066 is approximately 5 volts.
The two earpieces of the headphone are connected in series instead of in parallel for more audio signal.
Battery indicator (led off if battery low). The 2 band version is also given here as an option.
The receiver is quite good for large signal handling as needed for 40 m operation in the evening. Perfect QSO's have been made, also with a lot of QRP stations, even long chats using inverted V dipole antenna's with the centre at 4 meters height.
Sensitivity: 3 uV signals are readable
3rd intercept: 8 dBm
Spurious responses: Better than -90 dB
RX current: 10 mA
Transmit power: 0.5 W at 8 V; 1.5 W at 12 V
Harmonic suppression: below 30 MHz: 43 dB, above 30 MHz: 55 dB
Real simple technology....
BACK TO INDEX PA2OHH