Friday, April 16, 2010

68 dB bi-directional IF Gain stage and SSB filter using 4 MHz CPU crystals

After testing all of my 4 MHz CPU crystals i followed the procedures
in the 2010 ARRL handbook to design a 2 KHz bandwidth SSB filter.

I incorporated this filter into a bi-directional IF sub-system that i
designed using AD8009 current feedback op-amps (with 1 GHz GBP) and a
Motorola MC1350P IF amplifier, which provides 40 dB of gain and a
very nice analog attenuation for AGC.

Bi-directionality is achieved by the use of two dual pole two-way
relays. Some shielding had to be installed to eliminate a low-level
oscillation. As it is built no oscillation occurs in this stage.

Shown in the photos you can see the inside of the IF AMP built into a
Bud die-cast aluminum enclosure with an RF gasket. You also see the
IF amp connected to two DBM mixers, where, i used a pair of signal
generators as the VFO and the BFO respectively. In this
configuration i was able to tune in a local ham station using a wire
across the ceiling connected to the RF port of the front-end mixer.