"HIS TRX" for the hiker!
A two band 1 chip + 1 transistor
1 watt QRP CW transceiver

(2000)

KLIK HIER VOOR DE NEDERLANDSE VERSIE


Very simple CW transceiver for in
the backpack of the barefoot hiker!

Very simple rig for in the backpack!
This Barefoot QRP power transceiver is designed for the barefoot hiker. Barefoot, as his lifestyle is Back to Basics and that is what the HIS transceiver is. HIS is the abbreviation for He Is Simple! There is no side tone and no CW filter and not even a volume control. Weak signals are weak, strong signals are loud. Tuning range of the VXO is only 1 to 2 kHz. Back to Basics: portable in nature with the HIS transceiver and on bare feet.


Barefoot hiker portable in the
woods with the HIS transceiver!

Very much fun
It is small, simple and cheap. You do not have to be careful with it. If it falls into the mud or water or if it is damaged, no problem because it can be repaired very easily. And they certainly do not steal it!
It is very nice to take it with you on holidays to a unique location and to have the challenge to make QSO's with such simple equipment and low power.
The complete station is so small that it fits in a lunchbox, including antenna's batteries and logbook! You can have even more fun with such a simple rig than with your home station!


QRP station in a lunchbox for the barefoot hiker!

Portable in Nature.
The HIS TRX is designed for it! But making QSO's with the HIS transceiver is just as Back to Basics as walking barefoot in the snow instead of with snowboots! Although the performance is minimal, it is possible to make many QSO's with this simple set. It does not work always the first time, so do not give up too soon.

Just sufficient performance
This small rig is extremely simplified, no volume control, simple VXO tuning and the CW key is a pushbutton. The performance of the direct conversion receiver is just sufficient. But it is possible to make a lot of nice QSO's with this simple rig, even with other QRP stations.

The design
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.


Circuit diagram
big diagram

Mixer
The mixer is one C-MOS switch of the 74HC4066 (Do not use a HCT!!!). It works perfect!!!

LF amplifier
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.

VXO
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:

Crystal
Frequency
(kHz)
Minimum
Frequency
(kHz)
Maximum
Frequency
(kHz)
7030.0 7029.5 7030.8
10120.0 10119.3 10121.2

Transmitter part
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.

Notes
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.

Options
Battery indicator (led off if battery low). The 2 band version is also given here as an option.


Real simple barefoot technology....

Performance
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


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