Encyclopedia of radio electronics and electrical engineering / Civil radio communications
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A diagram of a simple signal generator covering the frequency band of 1 ... 30 MHz is shown in the figure. It was developed by DH1NAU and DB1NV to tune HF antennas in conjunction with a conventional resistive bridge. The output voltage of the generator is sufficient for normal operation of the bridge, if it uses a germanium diode, and the indicator has a total deviation current of no more than 50 μA.
The generator is assembled according to a push-pull scheme with capacitive feedback. The operating frequency band is divided into two subbands: from 1 to 9 MHz and from 9 to 30 MHz. Ranges are selected by switch S1 for two positions and three directions. Large frequency overlap on each sub-band implies the use of a large deceleration vernier variable capacitance with a capacitor. Otherwise, it will be difficult to set the operating frequency.
In this design, high-frequency transistors of the KT316, KT342 series and the like can be used. Variable capacitor - from the broadcasting receiver. The coils are wound on frames with a diameter of 8 mm with a carbonyl iron trimmer. Coil L1 (subrange 1 ... 9 MHz) has 60 turns of wire with a diameter of 0,8 mm. The withdrawal is made from the middle. The coupling coil L2 has six turns of the same wire. It is wound over L1 approximately in the middle (where the tap is made). Coils L3 and L4 have, respectively, 12 turns (with a tap from the middle) and two turns.
The signal generator is fed from a source with a voltage of 6 ... 9 V.
The original article (G. Grunbeck, J. Jirmann. Antennen Abgleich - autonom und netzunabhanig. - Funkamateur, 1998, No. 1, S.102-106) contains a description of two more signal generators - for bands 138 ... 150 and 400. ..450 MHz, as well as a description of the actual measuring bridge. Since this bridge is used on VHF, it is made on parts intended for surface mounting.
Authors: G.Grunbeck, J.Jirmann
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