i jectionahle. Since the receiver seemed fairly sensitive, checks were run on it to compare. The sensitivity ranged from 3.0¿iV for 20 dB of quieting at the low end to 5.5 /iV at the high end. (The usable, or threshold, sensitivity is actually much better than the "quieting" sensitivity, and is a more meaningful standard when no squelch is employed.)
Both receivers performed excellently with outside antennas. Because of their small size and low cost ($17.95) the receivers give the amateur portable coverage of the 6 and 2 meter FM frequencies as well as the 11 meter * and 10 meter amateur frequencies. The construction is excellent. The serious FM'er may want to crystal control the receiver for signal-channel operation. There is sufficient room inside the case for an oscillator circuit.
If the receiver is to be used at a fixed location, it is desirable to obtain the ac adapter (S3.95) which simply plugs into each receiver.
All in all, the Allied A-2586 and A-2587 are well wprth the small investment.
Have you ever wondered what kind of activity occurs on the 34 meter band? i suppose you've been curious, like many others, but not sufficiently so to go to the trouble of whipping up a converter or receiver to find out. Well, here is an extremely simple circuit which will allow you to determine if you would like to go to the expense and trouble.
Figure I shows the schematic of a simple transistorized superregenerative receiver which will work easily at 420 450 MHz. 1 his circuit provides exceptional sensitivity. If your hearing is good, you may connect a pair of earphones directly [o the circuit, although the level of audio is quite low. The more ambitious may, of course, build up a small audio amplifier, borrow one from an old transistor radio, or use an RCA CA3020 integrated circuit audio amplifier.
The transistor used is a relatively new device from Fairchild -a 2N49t6, which costs less than a dollar. This transistor is rearing its head as an excellent low-cost device featuring a beta of over 150 at 450 MHz-
No special parts have been used and the only problem area may be the choke in the audio output lead (RFC2), I used the secondary of a driver transformer from an old transistor radio. The value of inductance was around 160 mH. A choke closer to 30 mH would probably be better but doesn't appear to be too critical in this circuit.
Several liberties were taken with this circuit that may or may not appeal to you. Since I was interested in only one frequency, a "gimmick'1 capacitor (twisted leads) was used to tune the circuit to that btfcï JQ/2 5v btfcï JQ/2 5v
Fig, i. Schematic diagram of the Mighty Mite superregenerative receiver for the % meter band-
frequency. This also alleviated the work involved in providing an insulated shaft for a small variable capacitor. Other means are available for tuning this simple circuit, such as by shading L2. 1 his would provide a means of covering a spread of frequencies but would make the receiver more complex mechanically; and since 1 wanted to keep it simple, no attempts were made along these lines.
Figure 2A shows the foil side of the printed circuit board and 2B shows the
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