The AA-7, which can be built from scratch or purchased in kit form from the supplier listed in the Parts List, was assembled on a printed circuit board, measuring 4 by 4-11/16 inches. A template for the pcb board is shown in fig. 2. You can either etch your own board from that template, or purchase the circuit board or the complete kit of parts (which includes the pcb and all parts, but not the enclosure). The kit comes with a 16-page kit instruction manual that gives step-by-step assembly instructions and contains additional information not covered in this article. Kit assembly time, working slowly and carefully, should take less than an hour. Most of the parts specidied in the Parts list are standard components and can be procured through conventional hobby electronics suppliers. However, some parts--J1, J2, S1, S2, and R5-- have particular physical mounting dimensions; the Printed Circuit Board is designed to accept these particular parts. In addition, Q1 and Q2 can be hard to find; however, it is possible to make substitutions provided that you can find a supplier. Suitable replacements for Q1 and Q2 re given in the Parts List. The telescoping whip antenna screw-mounts to the board; the screw provides contact between the printed circuit board traces and the antenna. To save time and trouble locating and ordering hard-to-find parts, a Special Parts Kit is also offered by the supplier listed in the Parts List. A parts placement (layout) diagram for the AA-7's printed circuit board is shown in figure 3. When assembling the circuit, be especially careful that transistors Q1 and Q2, and the electrolytic capacitor C4, are oriented as shown.
Although not shown in the schematic (Fig. 1) or the layout (Fig. 3) diagrams, an optional led power indicator can be added to the circuit. Adding a power indicator to the circuit allows you to tell at a glance if the circuit is on; leaving the circuit on, even though the AA-7 draws only about 0.7 mA, will eventually discharge the battery. Of coutse, adding an led will increase the current drain to by about 7 mA, but the red glow makes it obvious when the unit is on. If you decide to include the indicator in your project, power for the indicator can be easily taken from the switched 9-volt DC terminal of S2 (center terminal, right side, looking at the top of S2). Simply connect the positive voltage to the anode (longer wire) of the led and connect her cathode lead through a current limiting resistor of about 1000 ohm to a ground point on the printed circuit board, or as the author did fromt the frame of R5. Mount the led at any convenient point near the switch. Although not supplied with the kit, a custom plastic enclosure (with front and back panels) or a regular 'hobby' case of some sorts, and knobs for the switches and gain control is offered in the Parts list. The enclosure comes pre-drilled and silk-screened with the appropriate legends for all the circuit controls and connecteors, but is not equipped with holes for the whip antenna or the led (if you include
Parts List and other components:
Semiconductors:
Q1 = MFE201, SK3991, or NTE454. N-Channel, dual-gate MOSFET (see text)
Q2 = 2SC2498, 2SC2570, 2N5179, SK9139, or NTE10. NPN VHF/UHF silicon transistor (see text)
Note: If you use the NTE107 as a replacement, make sure to insert it correctly
into the pcb. The orientation is different than as shown on the parts layout
diagram. (e-c-b seen frontview for NTE107). See this Data Sheet
Resistors:
All Resistors are 5%, 1/4-watt
R1 = 1 Mega Ohm
R2 = 220K
R3,R6 = 100K
R4 = 100 ohm
R5 = 10K potentiometer, (pc mount)
Capacitors:
C1,C2,C5,C6 = 0.01μF, ceramic disc
C3 = 100pF ceramic disc
C4 = 4.7 to 10μF, 16WVDC, radial lead electrolytic
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