This is it - several months of part-time contemplation, a full day designing the graphics, another two
days machining the sheet metal and wiring the circuit, and a final afternoon tweeking the values for
proper band coverage. It is about as tight as a passive device is going to get. I've tested several MFJ
preselectors, the Palstar, and Gilfer, but none are as tight (high-Q) as this configuration (you may see
typical response curves in the theory section). "Tight" to me is at least 18-24dB at 10 kHz off center
frequency.
days machining the sheet metal and wiring the circuit, and a final afternoon tweeking the values for
proper band coverage. It is about as tight as a passive device is going to get. I've tested several MFJ
preselectors, the Palstar, and Gilfer, but none are as tight (high-Q) as this configuration (you may see
typical response curves in the theory section). "Tight" to me is at least 18-24dB at 10 kHz off center
frequency.
This is the finished unit. The circuit worked out pretty good as designed, however it needed some
tweeking to get the bands to track better with a bit of overlap on the high and low ends. See the bold
figures in the original schematic
tweeking to get the bands to track better with a bit of overlap on the high and low ends. See the bold
figures in the original schematic
The "Selectivity" circuitry works as desired. The "Width" and "Depth" controls work fine, but now I question how
much use they'll get!
much use they'll get!
Here's the inside of the prototype. Looks pretty gutless...huh? Well, I wanted a big chassis since I'm
going to be experimenting with other modules. One is a crystal calibrator. All modern radios have
digital readouts, but I have a bunch that are analog. It will have a switch to mark at 10 kHz, 100 kHz,
and 1 MHz. I may stick in a DSP noise reduction module as well. Also much of the prototype wiring is
now RG-174 coax, even though the cabinet has a metal cover - it's just good practice.
By the way: Wiring colors are: red=B+, yellow=inputs, blue=outputs.
going to be experimenting with other modules. One is a crystal calibrator. All modern radios have
digital readouts, but I have a bunch that are analog. It will have a switch to mark at 10 kHz, 100 kHz,
and 1 MHz. I may stick in a DSP noise reduction module as well. Also much of the prototype wiring is
now RG-174 coax, even though the cabinet has a metal cover - it's just good practice.
By the way: Wiring colors are: red=B+, yellow=inputs, blue=outputs.
Type-5 Preselector FINISHED
