Beacon Transceiver Project

  
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DDS VFOs work very well with single conversion SSB radios such as the Codan 6801, 6924, 7727 and 8121, and the AWA Teleradio 110H. See the Recycled Radios page for more information about suitable Codan radios. Other commercial and marine transceivers with 1650kHz IFs should also be easily adaptable to a DDS VFO. There are numerous VFO kits around,
Beacon Transceiver Project - schematic

many of which are suitable for operation with a 1650kHz IF single-conversion transceiver. Check at the bottom of this page for the technique used to connect the VFO to the transceiver. In their original application these radios invariably offer only USB operation. Typically LSB operation is obtained by the simple expedient of operating the VFO below the required band, rather than above it. The image rejection on 160m may however be poor using this technique. Otherwise image rejection should be good up to 15MHz or so. If operating with the VFO below the required band is not appropriate to your application, you will need to find a way to add an extra crystal filter, or a second BFO crystal. Whichever VFO you choose, make sure that the off-frequency spurs generated are low. Generally the spurs won`t affect the transmitted signal, but a spur 40dB down may cause a strong short wave broadcast station to be received when you least expect it, in the middle of a ham band. Phase noise on the VFO will have a direct impact on the sensitivity of the receiver, and will also affect signal quality on transmit and receive. DDS VFOs inherently have low phase noise. The Si570 type also have acceptably low phase noise for HF operation. You can connect the DDS VFO (or any other VFO) to as many channels as you like, and leave the others crystal controlled. For each channel you connect, you will need a 10nF ceramic capacitor, and of course...



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