"Minimal 1", QRPp transmitter for 20m CW

I like to design and build minimal electronics. QRP and specially QRPp can be really minimalistic.

It is often easier to make complex solutions than simple one's. In minimalistic design the product is improved by taking parts out.

It becomes minimal when you cannot take anything more out.

In this transmitter output power is minimal, 1W. And so is the number of components. In the basic version there are 17

components, if switches, connectors and power supply are not counted. There is only one transistor.

In the version with grounding key there are two more resistors and one transistor, making total 20.

How about performance and cost?

Second harmonic is 44dB down and third harmonic -60dB, which makes this TX to meet regulations. Efficiency is about 70%.

The transistor BC337 cost 0.10 Euros and has no heat sink. The most expensive components are the XTAL and toroid cores

With 14060kHz XTAL frequency can be tuned at least between 14055-14060kHz, or more.

The transistor operates between class C and E. Its loading is carefully done. The transmitter was designed with modeling tool

Capacitors and inductances were selected or tuned to specification with 2% accuracy.

No tuning or trimming was necessary other than DC bias. Because of spread in transistor current gain, resistor

R3 had to be adjusted. Having 50 ohm dummy load in place key down current was set to 110mA with R3.

For frequency tuning a serial reactance with the XTAL is changed. On capacitive side it can be varied from 33pF to infinite

and on inductive side up to 2uH. I used a rotary switch, fixed capacitors and inductance for that. Variable cap would be even better.

My construction method was the ugly style on a piece of PCB material. Having just few components it become almost beautiful.

I did not use connectors at all but soldered 1m long pig tail cables and have plugs in their ends. Minimal also this way..

In one week I worked more than 30 QSO's and 14 countries including U.S. with this minimal transmitter. My antenna

was 2-element Moxon 16m high.

It is really fun to get a DX contact with such a simple equipment. It feels better than to get country # 300 with full legal power

and commercial equipment. Amateur radio is an extreme sport. You can increase your challenge in different ways.

One way is to reduce output power and number of components used in your radio. That is like minimal art.

Pekka OH1TV, OH1WX on QRP

23.11.2009

26.12.2009