HAM RADIO

Receive Amateur SSB And CW signals on your  shortwave radio

 

Since most amateurs switched from AM to single sideband, it hasn't been possible to receive them with an unaided shortwave receiver. All you'd hear is garbled 'duck talk'. Here's the solution. It's a one-transistor beat frequency oscillator that makes amateur SSB signals intelligble on a cheap receiver. It is an ideal project for the aspiring amateur, as it allows them to monitor amateur activity. Its usefulness, low cost, and ease of construction would make it a good group project for schools, radio clubs or amateur theory classes. The device is a miniature transmitter. It provides a steady carrier signal to the receiver to replace that suppressed within the transmitter (refer to any radio theory book for a more detailed explanation). It is the ultimate in simplicity, employing but eight components. The unit costs approximately ten rupees to build from all-new parts, and requires no alignment or connections to the receiver. Anyone with basic soldering skills can construct this project, and have it working first time. Though receivers covering the short wave bands are no longer in every home, suitable sets can be picked up cheaply at garage sales and swap meets. Tuning the medium wave and one or two short wave bands, their performance is lacking in many respects. Nevertheless, they work better than might be expected when used with this circuit. The reasons for this are given later. Circuit Description This unit is a one transistor 455 KHz RF oscillator whose frequency can be varied. As mentioned before, it replaces the carrier in the receiver that was suppressed during the transmitter's SSB generation process. An IFT of old transistor radio sets the oscillator frequency. It is still acceptable for stable SSB reception. Because the BFO operates directly on the receivers’intermediate frequency, many of the limitations of low cost AM receivers (such as frequency drift, coarse frequency readout, hand-capacity and difficulty of tuning) are either eliminated or made less apparent. This is because the tuning in of SSB transmissions is effectively performed by a stable, easy to tune BFO, rather than the unstable free-running coarse-tuning local oscillator within the receiver. The circuit permits reception of CW and SSB activity. Construction Virtually any construction method may be used to assemble the BFO. Several prototypes were built. Almost any construction technique can be used. Whereas most RF projects are built in metal cases to provide shielding, the BFO's operation depends on there being a lack of shielding between it and the receiver. Thus either a plastic or wooden box is recommended. Operation To verify BFO operation, your AM short wave set is required. Position the receiver near the BFO, and tune it to 455 KHz frequency range. At a certain point the receiver will go quiet; all normal background noise will be silenced. Switching off the BFO will restore the normal band noise you know that it works. Now switch off the BFO, attach a piece of wire from BFO to the receiver's IFT side and then switch on, and tune in a strong SSB signal for maximum volume it will be possible to resolve the signal by the BFO.Then decreace the radio volume until the SSB signal is intelligible. Note that the BFO's frequency must be more or less equal to that of the intermediate frequency of the receiver.  Video demonstration of the BFO Conclusion A novel device to allow the reception of amateur signals on domestic AM-only short wave receivers has been described. It is cheap, very simple to build, and can be expected to work first time. It fills a definite need amongst potential amateurs, and has the advantage of being expandable to a direct conversion receiver or CW/DSB transmitter or transceiver as interest develops. Note: This article is that appeared in Amateur Radio, October 1997. 3.58 MHz ceramic resonators.