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Multi-band, Direct Conversion CW Transceiver (MBDC)
The Multi-band, Direct Conversion CW transceiver (MBDC) is designed primarily, and furnished, for operation on the 160 and 80 meter ham bands, with details on how to change the two bands to any of the 40m, 30m, 20m, and 17m bands. The wide tuning range of the DDS VFO also allows for general coverage tuning of 100 kHz to 21.5 MHz and the Direct Conversion receiver allows for the reception of all modes.
Three receiver audio bandwidths are available and are selected with a push button on the front panel. AGC and independent volume control prevents ear shattering volume levels with very strong stations.
160 and 80 meters was chosen for the stock operating bands for two reasons. One, there are not many kits available for these bands. Two, the Direct Conversion receiver is best used on bands which are generally not all that busy or crowed. Operating a DC receiver on the busy 40 and 20 bands can be very frustrating!
For use outside the 160 and 80 meter ham bands a separate auxiliary receiver antenna input is used. This by-passes the transmitter low pass filters and a 1.7 MHz high pass filter which would limit reception to the two ham bands. The auxiliary antenna input can also be used on the selected ham band if desired, as it can be desirable to use a dedicated receiver antenna on the top bands to reduce noise pick up.
The auxiliary receiver antenna input goes directly to the mixer without any filtering or tuning as this would seriously complicate the design and expense for general coverage tuning. Also, the receiver is not overly sensitive as there is no need for it on the Top bands. Too much sensitivity would just raise the noise level and degrade the S/N ratio. Note that the receiver is also sensitive to stations at the second harmonic of the LO.
Therefore, adding some sort of pre-selector and possibly a pre-amp would be helpful when used as a general coverage receiver, which is another reason for including the auxiliary receiver antenna input.
An open Drain MUTE output is available for control of a pre-selector or for the control of an external linear amplifier.
Because of the wide frequency tuning available with the DDS VFO, it would be a shame not to allow full use of this capacity. Therefore, it is possible to program the MBDC rig to operate on bands other then 160 and 80 meters. However, it is not a good idea to use the transmitter above 17 meters due to possible stability problems and the fact the transmitter output filter becomes very touchy above 18 MHz.
Unless programmed differently, the transmitter is only enabled within the limits of the 80 and 160 meter ham bands. If you tune out side the currently selected ham band, the transmitter will be disabled and this is indicated by a [ * ] in the upper left of the display.
Limits can be programmed so that the transmitter is enabled between two
frequencies of your choice. These are typically the high and low ends of the
given ham band. However, if use as a signal generator is desired they could
be set to the tuning range of the DDS VFO, 100 kHz to 21.5 MHz. Programmable
limits also allows setting up the rig to use on the LOWfer bands.
MBDC V2 Construction Manual
MBDC Decal Instruction Manual
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