Antennas

Table-lop the Main Features . . . Indoors

Try reflector and director lengths, spacings, numbers, combining yagis, extended-expanded collineais, V* wave, Vi wave, and two-half waves in phase for 160 and SO meters right inside your shack!

Complete construction details for an antenna test set of 432 MHz. Easy-to-build units; a 432 MHz oscillator and a tuned detector are detailed for you. These rf units may be used later to build a complete hand-carried solid state portable station on 432, with superhet receiver. This station is described in 73 Magazine in the article "The 432'er Solid State."

With care and using a small iron you can also test spare or surplusVHForUHF diodes and transistors lying around the shack, by substituting them in these r/sets. Oscillator Construction.

Figure 1 is the oscillator schematic. A UHF transistor, like a 918 or RCA 2N3600, is used in a grounded-base circuit, which makes it a good oscillator right away. The copper strap over copper-clad baseboard results in quite a high-Q circuit, is easy to couple out of, and tunes over a lot more than just the 420 to 450 MHz amateur band, unless you wish to pad it down and/or remove plates from the Johnson type M capacitor. An output coupling capacitor is provided for better adjustment to the 50 ohm output cable.

Figure 2 is a top view, and Fig. 3 is the side view. This unit is similar to the one in the

"432'er, Solid State" article in 73 Magazine, making it easy to transfer it into the complete rig described there later on, if you wish to do so. There is a slight difference in the dc bias network because in antenna test work a lot (like 100 milliwatts!) of power is desirable, while for local oscillator service in the superhet receiver, lower harmonic content and less power are wanted. Tuned Detector Unit.

The schematic is in Fig. 4, the top view is Fig. 5, and Fig. 6 shows the side view. The detector diode unit is also similar to the "432'er" mixer unit, except that the if coil is not installed and the dc output is brought out of the if jack. Be sure to leave space for the if coil if you want to use this detector later on as a mixer. Operating the Antenna Test Sets.

After building the rf units, set up two card tables, one for the oscillator and transmitting antenna test units, the other for the receiver antenna and tuned detector, as in block diagram.

Next step. Go over to the other card table and set up the tuned detector. This is very convenient for indoor work, as you will see. For checking directivity, good gain measurements. Getting away from the "near field" are some of the reasons for the two tables.

The diode detector needs no battery but you will need a good meter, which should be a 50 mA unit for best sensitivity. You can use a heavier meter, but it will just not be as

0 0

Post a comment