This is a very lower power ham radio transmitter using a solar panel (designed for charging a mobile phone) as a power source.

Step 1: A Solar-Powered Very Low Power (QRPp) Transmitter

At Leicester Hackspace we had the opportunity to use donated 5 volt solar power boards for new projects. Many thanks!

As a radio "ham" I'm interested in using low powered transmitters to see how far these weak signals can get. I also use similar surplus frequency-set oscillator blocks to adjust and calibrate receivers.

As these use a 5 Volt supply it seemed a natural choice for this project.

Figure 1 shows the very simple circuit - from an auction site serach for

"28.636 MHz Crystal-Controlled 10-Meter Band QRP TRANSMITTERS"

It's a simplified vesrion of the device used at http://www.fpqrp.org/BBITS/bb0501.pdf (inside the magazine).

My choice of a frequency of 28 MHz is because on the receive side the cheap RTL dongle operates above 24 MHz so together this is a very inexpensive tx/rx combo.

I'll be using a Morse code key in this exercise.

Step 2: Adding a Filter

Because in this application I don't want to calibrate using the multiples of the frequency of the block, I need to suppress these multiples or "harmonics", so I need to put a filter in line between the antenna and the transmitter block, as above.

There are only two types of components - three of them are capacitors and two of them are coils. Use the values as search terms and you'll find them.

Step 3: Simple Construction - Top Side

So here's the top side, with the filter to the left of the screen following out the antenna and earth lines . (As a Brit I say "Earth" not "Ground"!)

Step 4: Solder Side

As you can see I'm not very elegant at soldering!

But you can see here that the negative line (black) from an old USB cord goes to the earth line, and the red line, which is +5v, will go to the oscillator block.

The USB connector will plug into the solar panel directly (or you can add a float battery).

Step 5: Here's the USB Power Connector.

I'm only using the red (+5V) and black (earth) lines, not the data lines.

Step 6: Morse Key

This is an old key that I bought in a flea market in Ukraine some years ago.

The red line from the USB cable goes into the central ridge of the key, and the front ridge of the key will be connected to the oscillator block marked +5v.

There are small screws into the ridges that will hold the wires.

So I am keying 5 volts at a very low current.

The sound it makes is a bit like bird chirps so we call it "chirpy".

Step 7: Connecting the Solar Panel

And here you can see that the solar panel does not have a charger circuit but goes almost straight into the red and black power lines. Note that I've folded up the panel in this photo so that the workshop lights don't cause a positive voltage to appear across the circuit when I don't want it.

Here I have connected the charger to the float battery and the battery to the transceiver. So i can charge during the day and transmit at night.

Finally I put two lengths of wire, each about 2 and a half metres long, on the antenna and the earth lines - the combo is called a "dipole" and the length is optimal for this frequency - and hang the wires spread out from a tree or something in the garden.

Directing the solar panel charger towards the sun will cause the red light to come on, power will flow either trough the battery or direct through the key, and you can send Morse code on the 10 meter ham band!