1 Volt transceiver for 80m CW

I had earlier built keyers using 1.5V battery as a power supply. Next challenge was to try to make the whole station using

1.5 Volt batteries as power source. Designing circuits, which work with that low voltage was my motivation for this project.

The work of DL2AVH and DL4ALJ with 1 volt rigs inspired me too.

In the end of the project I learned, that low voltage at the transistors was not the main limiting factor for transmitter power.

It was the internal resistance of the battery.

200-300mW output power is about the maximum RF power you can get when using a standard battery like LR20.

This is a transceiver with VFO and direct conversion receiver. CW filter is passive with coils and capacitors. It is sharp and pleasant.

There is no AGC. You shall adjust the audio gain instead.

Attached are the schematics. They are basic bipolar circuits. RF chokes are used in many places where otherwise

resistors would be seen. (if the voltage was higher).

I tested many different mixers. CMOS analog switches would have been my choice if they worked with 1.5V. But they do not.

This four diode shunt switch was the best. It is free from intermodulation from AM-stations. The idea is from AA1TJ.

Stability of VFO seems not to be function of voltage used. Rather it is function of component stability. Big coil, no trimmer capacitors,

silver mica and NP0 capacitors, permeability tuning, diacast housing are the secrets.

When transmitting, the VFO is tuned 800Hz down by switching additional capacitor C9. In receiving the VFO shall be tuned

800Hz above the received signal. VFO is above the received signal when: tuning up the band, frequency of audio signal increases.

This way you will transmit on the same frequency as the other station.

To avoid voltage variations in VFO I have a small separate 1.5V battery for it.

TR-switching is with a toggle switch. Simple is beautiful.

My output power is 200mW. I have been surprised how good reports that low power can give. Daytime reports in OH-land have been

between 559 and 589 from hundreds of kilometers away.

Few words about my construction: I have five modules which are natural choices when testing the circuits. Mixer pre-amplifier and

transmitter power amplifier are built ugly style on pieces of PCB and shielded with sardine can.

VFO is in die-cast aluminum box. CW filter and AF power amplifier are on pieces of PCB, ugly style. Inter-module signal wirering is

with mini coax cable and RCA style connectors.

This was an extreme project, from the very low end ; ) Real fun!

Pekka OH1TV

7.4.2009

Block diagram

Mixer & audio pre-amplifier

CW filter

Audio power amplifier

VFO

Transmitter power amplifier

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First QSO's. My call here OH1WX. Antenna is dipole, up 10m.

Day

UTC

Station

Received

Sent

Band

Mode

Name, QTH

5.4.2009

15:20

OH1NDW

589

599

80m

Jarmo, Hämeenkyrö

5.4.2009

15:30

OH3IH

579

599

80m

Reino, Pirkkala

5.4.2009

15:42

OH7OL

579

599

80m

Reino 79years, Joensuu

6.4.2009

14:15

OH6VI

559

599

80m

Heikki, Vaasa

6.4.2009

15:10

OH1CY

579

599

80m

Tapio, Ikaalinen

7.4.2009

14:32

OH1NM

559

599

80m

Reijo

7.4.2009

14:38

OH4RW

569

579

80m

Mara, Pieksämäki 5W

7.4.2009

14:52

OH1MA

559

599

80m

Jaska

10.4.2009

6:30

OH0LQK

599

80m

10.4.2009

6:42

OH1SR

559

579

80m

Rai, Korpo, 50W

10.4.2009

6:30

OH5LP

449

80m

Seppo, Pieksämäki, Kyynel