MY FIRST QRP RIG "THE BAREFOOTER"


An ultra portable QRP CW-transceiver for 20 meter.

Simple!
Indeed the rig is really simple! When I found the design, I did not believe that it was possible to make QSO's with it as its simplicity is such a contrast with the standard amateur transceiver with high power, superhet receiver and other complex circuits.
But it should be a very nice experiment to take such a simple transceiver with me on Holidays to Norway and Sweden!

Holidays
Within two weeks this 20m QRP rig was ready to take with me on holidays to Norway and Sweden. And results were astonishing! Almost every day it was possible to make a QSO with a radio amateur living nearby my home QTH. With ease, also a lot of other QSO's were made. The antenna was a dipole between trees when camping in the woods. Little stones or branches are used to throw the ropes in the trees. Or the same dipole is also used as inverted Vee with the center at 4 meters using a fishing rod. Also a quarter wave vertical, using the same fishing rod, 6x2meters radial wires as groundplane was used.
All antenna's worked well, I never had an SWR meter with me. The vertical with the radials was made from loudspeaker wire and a PL259 plug, sold in a local shop in Sweden. The wire length was calculated and I never verified the SWR...
As this simple rig worked much better than expected, I also made a two band version for 40 and 20m.

MY FIRST QRP RIG

The design is based on an article in the book Solid State Design for the Radio Amateur
In fact I do not need to explain everything in detail, just look at the schematic diagram and you will recognize most items. The VXO is used as the local oscillator for the direct conversion receiver and drives the final amplifier when transmitting.


Circuit diagram, sorry for the Dutch language.

Mixer
The mixer is an old chip, the CA3028. There are better and cheaper one's like the NE612. As the mixer is not symmetric, the receiver is sensitive for AM detection of strong broadcast stations.

LF amplifier
The coupling between the two transistor LF amplifier and the mixer is via a LF transformer. And that is a problem if you use the rig nearby power lines or transformers, a loud 50 Hz hum is heard. I took a LF driver transformer of a balanced final LF amplifier from an old transistor radio.
The two transistor LF amplifier drives the earphones. Connect both earpieces in series instead of in parallel for much more audio output.
During transmission, the side tone generator is coupled via the 2M2 resistor (select it for the side tone level you want to have) to the LF amplifier. Although there is not so much selectivity, the receiver sounds good and I always listened to it with pleasure. The 2k2 potentiometer is for the battery-empty indication. Connect the rig with the minimum supply voltage. While transmitting, adjust the potentiometer so that the side tone dissapears.

VXO
The VXO frequency is varied by a simple variable mica capacitor. Via the 5 pFcapacitor, the VXO signal is fed to the mixer.
I used two crystals: 14045 and 14060 kHz, but of course you can use any frequency you like.
For the two band version, the 120 pF capacitor is removed and the tuneable coil is replaced by a FT37-43 ferrite core (same windings) and I use only one crystal per band.

Transmitter part
The VXO signal is amplified to 1 watt by a transistor 2N3553. The output is filtered in two pi sections. Why is switch S1b in the middle of the filter instead of at the end? I really do not know. In the two band version I used two 5 pole filters and switch S1b at the end of the filters. Solder a 100 pF capacitor between the collector and emitter of the 2N3553 for stability reasons.


The inside view, all "Simple QRP" technology.

Notes
The CW key is a simple microswitch. When you see the photo's, you do not need a further explanation. In the 2 band version, I used an extra PNP transistor, so that the key is connected to ground.
The two earpieces of the headphone are connected in series instead of in parallel for more audio.
For the two band version, I also added a 1k potentiometer between S1b and the receiver for RF volume control.

Performance
I have had a lot of fun with this rig and used it during holidays under all kinds of conditions. It always worked fine!
The receiver is sensitive enough, some AM detection of strong broadcast stations is possible, the audio transformer gave problems when camping close to overhead power lines, there is no volume control, but it was real fun to use this rig. The antenna was a dipole between trees or as inverted Vee, the middle at 4 meters using a 5m fishing rod as a support. I also used a vertical (vertical wire mounted to the vertical fishing rod and 6 radials of 2 m length).
The rig is also used in the shack with a long wire antenna and a tuning unit. A lot of perfect QSO's are made, even long chats.
I also designed a new version, the 4 band HappyHoliday trx, also somewhere on this site.

RX current: 30 mA (quite high)
Transmit power: 0.6 W at 9 V; 1.5 W at 12 V
Harmonic suppression: Yes!


The two band version of the Barefooter and the original
article in the book Solid State Design for the Radio Amateur.

BACK TO INDEX PA2OHH