Tuesday, 15 February 2011

TOBACCO TIN TRANSMITTER

 

I would like to show you my novelty transmitter project which I have enclosed into a tobacco tin. It requires very few parts, they are very easy to obtain, most of them came from my junk box with the exception of the crystal (7.030 MHz) which is an international QRP calling frequency. Any crystal will do as long as the operating frequency is within the amateur band, preferably in the CW section.

CIRCUIT

This is a one transistor crystal controlled transmitter, it uses the 2N2222 transistor in a basic oscillator arrangement, and has a simple output filter section for any unwanted harmonics. If the output filter was not used  the transmitted frequency would not only be 7.030 MHz but also 14.060 and 28.120 MHz etc. These unwanted frequencies are called harmonics. The output power is only 250 milliwatts (quarter of a watt) but high harmonic output is illegal even at this low power.  

CONSTRUCTION

I have used the ugly style construction, this is where you start with an off cut of copper clad board material, and build the circuit on the copper side up. The copper surface makes a low impedance ground and a anchor point for components. The grounded or copper surfaced components make a good solid support for the rest of the circuit to be built on. It is up to you as the builder which style you use, but the ugly construction is a lot cheaper than buying expensive vero board or making a printed circuit board. As you can see from the diagram there are very few parts, and it is straight forward to build. RFC1 is 6 turns of 32 s.w.g. enamelled copper wire wound on a tiny ferrite bead, any thin wire and ferrite bead should work. The toroid in the output filter section is 14 turns of 26 s.w.g enamelled copper wire wound around a T50-2 core.

OPERATING

When you have finished just press your morse key, no tune up procedure is necessary. You will also need an HF receiver, or shortwave radio with a BFO to operate with, I use a Realistic DX-394 receiver with an indoor wire and the transmitter next to the receiver with any of my outdoor antennas, but you could operate both from one antenna with a changeover switch. Although the transmitter only has 250 miliwatts this circuit when connected to a good outdoor antenna such as a dipole in favorable conditions has worked DX over 7000 miles. You will notice I have left a space on the right hand side of the box, this is to put an optional PP3 9 volt battery inside if I am going portable.

OTHER BANDS

The transmitter can also be  built to work on 80, 30 and 20 meters with the crystal of your choice, and the following changes=

80 meters =T50-2 toroid 21 turns capacitors 1, 2 and 3 =750 pfd

30 meters = T50-2 toroid 13 turns capacitors 1,2 and 3 =330pfd

20 meters =T50-2 toroid 12 turns capacitors  1, 2 and 3=270pfd

Please note It is illegal to operate this transmitter without an hf license.

http://www.gameangler.eu/delboy/m0dad/construcion/tobacco_tin_transmitter.htm

1 comment:

  1. Tx would not oscillate after built.

    ReplyDelete