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Wednesday, November 13, 2013

Ham Radios - BITX - An easy to build 6 watts SSB transceiver for 14MHz

I always wanted to learn how to build a Radio or TV Transmitter. Especially a low Powered TV Transmitter. That I could actually use at home. I have loved electronics, since I was a kid. And have done allot of Audio Recording and Live Sound Mixing, over the years. I worked at a small TV Station, as a Master Control Operator. And got to learn a bit about TV Transmitters Worked. I worked in the actual TV Tower Building. But, I never found my self very interested in Ham Radio. It seemed to have a very large learning curve. And I'm not really a big talker. So, I never really dreamed of spending hours talking to people on a radio or any other device. I don't like talking on the phone either... I use to always have several Auto, Wood or other type of Protects going at the same time. Now days, I like to read about interesting projects. And build things too. When I can. But, this Ham Radio Project, looks simple enough to make it very interesting to me. Even if I hardly ever talked on it. Check i tout...


BITX - An easy to build 6 watts SSB transceiver for 14MHz

BITX is an easily assembled transceiver for the beginner with very clean performance.
Using ordinary electronic components and improvising where specific components like toroids are not available, It has a minimum number of coils to be wound.
All alignment is non-critical and easily achieved even without sophisticated equipment. The entire instructions to assemble the rig are given here along with relevant theory.

The Indian hams have often been handicapped by a lack of low cost equipment to get them on air. A mono-band, bidirectional design using ordinary NPN transistors was developed to cater to this demand. The design can be adapted to any particular ham band by changing the RF section coils and capacitors and the VFO frequency.

BITX evolved over one year from the excellent S7C receiver described in the new ARRL book ‘Experimental Methods in RF Design’ (an ARRLpublication) into a bi-directional transceiver. Several hams across the globe contributed to its design. A series of emails were exchanged with OM Wes Hayward (W7ZOI) during the evolution of this design. His contributions have been invaluable. He urged me to strive for higher performance from the simple design. The resultant rig has sensitive receiver capable of strong signal handling, a stable and clean transmitter capable of enough power to make contacts across the World.

All the parts used in BITX are ordinary electronic spares components. Instead of expensive and hard-to-get toroids, we have used ordinary tap washers. Broad-band transformers have used TV balun cores. The entire transceiver can be assembled in India for less than Rs.300. I have designed a single side PCB with large tracks that can be easily etched at home or by any PCB shop. They are also available from OM Paddy, (VU2PEP,

For those who don't read long articles ...

There are a couple of things you should know before you start assembling the circuit:
  • The same amplifier block is used throughout. But the emiiter resistors vary in some of the places. Double check the values. If you swap values, the circuit won’t stop working. It will work terribly. That might be a little difficult to diagnose in the end. Check the emitter values and the resistors that go between the base and collector.
  • The receiving IF amplifier between the filter and the product detector is coupled to the product detector using a 100pf (not 0.1uf).
  • The crystal filter worked for me, I used crystals from the local market marked as KDS. These are the cheapest and they work with the capacitor values given in the filter. Your crystals might require a different set of capacitors. Try the values given here, if you find the bandwidth too narrow, decrease the capacitances, if you find it too open then increase the capacitances.
  • The microphone is directly coupled to the amplifier as my headset microphone needs 5V bias. If your microphone works without bias, then insert a 1uf in series with the microphone.
  • The pictures show my prototype on two boards. Don’t do that, split up the VFO into a separate box.
  • The pre-driver is built onto the main board. The driver and the PA are on a separate board. Keep the same layout to keep the PA stable.
  • There is a 50uf on the power line soldered near the BFO, don't forget it. It cleans up the audio noise which would otherwise get into the receiver.
  • On the PCB, there are jumpers between T lines and R lines across the ladder filter. There is a jumper from the BFO supply to the VFO supply.

Ham Radios - BITX - An easy to build 6 watts SSB transceiver for 14MHz

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