Wednesday, April 28, 2010

testing the signal chain

Connecting the front-end mixer to the bi-directional IF amplifier/
filter to the product detector. Using two bench signal generators,
one for the VFO the other for the BFO, i could tune in local HAMs on
20 m with a simple wire antenna.

More to come....

Saturday, April 24, 2010

Tuesday, April 20, 2010

front end mixer

Here is the front-end mixer module. Inside this module you will find
a double balanced mixer with a 14.25 Mc, 500 Kc BW front-end filter,
a 4 MHc 1 MHz BW IF filter, and a 3 dB LO PI attenuator.

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.

Wednesday, April 14, 2010

building an SSB transceiver from scratch, step 1: testing surplus CPU crystals

A SSB filter crystal filter can be built out of surplus CPU crystals,
according to the 2010 ARRL handbook. I have found large volume of 4
MHz CPU crystals and have characterized all of these in order to
design my SSB filter. I use a spectrum analyzer, frequency counter,
and a phase-locked signal generator to characterize the series,
parallel resonances and the series resistance. I use an LCR meter to
find the parallel capacitance.

I will use these old crystals to design a suitable 2 KHz SSB filter.

Stay tuned for the results....