Mar

132 MHz

Figure 1—Block diagram. FL1 (optional) permits the use of any IF from 21 to 148 MHz.

Jan/Feb 1998 41

Fabrication

The mixer circuit board is a double-sided Vi6x3 '/4x6 inch PCB. Fig 7 shows the layout. Parts not shown, mainly the post amplifier, are mounted on the PCB's opposite side. LO circuit-board layout is much less critical, so it is not illustrated. It uses a 4'/2x6 inch base PCB. The layouts of both circuit boards generally conform to that of the schematic.

The MMICs, diodes and trimmer capacitors can be purchased from Down East Microwave Inc.1 Most of the other parts can be purchased from Radio Shack. For example, the low-value disc ceramic capacitors are in their "picoFarads 50-Pac." You can use Radio Shack double-sided PCB, but with a minor performance compromise. In a test SBM model using Radio Shack PCB, the balance was good and the operation seemed competitive with that of a glass-epoxy PCB. Loss in the phenolic dielectric can not be overlooked, however. In addition, foil adhesion in phenolic boards is poor compared to that of glass-epoxy PCB.

Note that Radio Shack phenolic PCB has a glue-down stripline propagation constant of 0.64 rather than the 0.61 used for the glass epoxy PCB. This is of little consequence except for its effect on the mixer stripline lengths. Fig

8 shows nominal test-point values.

Performance

The only 2.4 GHz test device I have is a Noise/Com2 NC-302L diode with an excess noise ratio of 30-35 dB up to

Figure 2—Schematic of the mixer circuit

Parts List

2835 or equiv.

Figure 2—Schematic of the mixer circuit

Parts List

2835 or equiv.

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