An effective method of excitation of RA. Scheme, description

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An effective method of excitation of RA. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / RF power amplifiers

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I want to share my method of powerful enough buildup PA QRP transmitter. The scheme from the book by S. Bunimovich and L. Yaylenko "Universal exciter for a powerful mind" was taken as a basis. The impetus for this was a conversation with RW3QF. A transceiver with a power of 3-4 W and an amplifier with two GMI-11 lamps achieves a power gain of 24-36 dB. At an anode voltage of 500 V, the current reaches 800-900 mA with a slight drop in the HF ranges (Fig. 1).

Through a biscuit switch or relay, each range has its own resonant circuit. There is only one drawback: each circuit has its own range. The advantage is the effective suppression of out-of-band emissions. Harmonics on higher frequency ranges are practically absent.

Fig.1 (click to enlarge)

By shifting the tap of the resonant circuit in one direction or another, excellent impedance matching between the transceiver and the RA is carried out. The circuit has a narrow resonance, therefore, when tuning, it is advisable to turn on the KPI in parallel with it and adjust the RA for the maximum current, and after tuning, solder the constant capacitance. If it is not possible to mount all the circuits on the board, an alternative connection can be made (Fig. 2).

An effective method of excitation of RA
Ris.2

Several taps and KPI displayed on the front panel allow switching up to three ranges. If it is necessary to galvanically decouple the transceiver from the RA, the circuit is connected via a coupling coil. The contour data are taken from the book by Ya. Lapovka "I am building a KB radio station" and are given in Table 1.

Range	2V MHz	21 MHz	14 MHz	7.0 MHz	3.6 MHz	1.8MHz
Number of turns	3 + 3	1 + 1	5 + 5	9 + 9	15 + 15	25 + 25
PEV	0.63	0,55	0.55	0.1	0.4	0.3

All coils are wound on frames from the IF circuits of the TV. In this way, you can swing any lamp at the lowest possible input power. Attention should be paid to the possible pumping on HF.

All coils with diameters of 7 ... 8 mm from the contours of the IF of the TV.

Author: V.Milyaev (RZ3QG), Voronezh region, Buturlinovsky district, r.p. N. Kislyay; Publication: N. Bolshakov, rf.atnn.ru

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