Broadband transformer with a transformation ratio of 3/2. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Broadband transformer with a transformation ratio of 3/2. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Nodes of amateur radio equipment

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Modern equipment uses broadband transformers on long lines (TDL). In amateur radio literature [1], only TDLs with integer voltage transformation ratios nu=1,2..., respectively, having a resistance transformation ratio ni=nu=1,4,9..., are described. However, it often becomes necessary to have pi=2. The TDL is described below, having a fractional ni=3/2 and ni=2,25 [2].

TDL consists of three lines W1 - W3, having the same wave impedance p and length l (Fig. 1). On the rising side, the lines W2, W3 are connected in parallel so that the resistance between the terminals 3' - 4' is p / 2, and in series with them - the line W1 with a resistance p so that the resistance between the terminals 1' - 4' is Rout = 1,5p. On the lower side, the lines W2, W3 are connected in series, and the line W1 is connected in parallel so that the resistance between terminals 1 and 2 is determined by the parallel connection of 'p (W1) and 2p (W2, W3) and is Rin = 0,66p. In this case, n1=Rout/Rin=2,25.

Broadband transformer with a transformation ratio of 3/2
Ris.1

An analysis of the low-frequency equivalent circuit shows that the common-mode voltages on the lines W1, W2 are the same in magnitude and anti-phase, and on W3 it is equal to zero. That is, when performing TDL on one magnetic circuit, W1 and W2 must have the same number of turns and the opposite direction of winding, and W3 should be located outside the magnetic circuit and have the same length as W1, W2.

Broadband transformer with a transformation ratio of 3/2
Ris.2

On fig. 2 shows the wiring diagram of such a TDL. Linl W3 does not have a common-mode voltage and only compensates for the phase shift introduced by W1, W2, so if the line length is less than l/8 of the wavelength and a very wide band is not required (no more than two or three octaves), then W3 can be replaced by jumpers (Fig. 3).

Broadband transformer with a transformation ratio of 3/2
Ris.3

The calculation of the number of turns and the choice of the type of magnetic circuit can be carried out according to the method [1].

Possible options for using TDL, made in accordance with Fig. 3, for matching antennas are shown in the table.

N	Rout (Ohm)	p(0m)	Rin (Ohm)	Application
1	33	50	75	GP matching, or HB9CV with cablelem 75 ohm
2	50	75	112.5	Coordination of the frame with the perimeter equal to the wavelength and large suspension height with a 50 Ohm cable
3	25	37.5 two 75 ohm lines in parallel	56	2 - 3 element YAGI matching with 50 ohm cable

TDL 1,3 are wound on a magnetic circuit 100 NN K45x28x8, and have two windings of 13 turns each, the bandwidth is 10 - 30 MHz. TDL 1 is wound with a 50 Ohm cable, TDL 3 in two 75 Ohm cables connected in parallel. TDL 2 has a bandwidth of 7 - 30 MHz and is made on a magnetic circuit 50 VN K65x40x9 in two windings of 15 turns of a 75 Ohm cable. All three TDLs are designed for a power of 200 watts.

Literature

V.Zakharov. Matching devices on ferrite magnetic circuits. Radio 1987. No. 6, pp. 26 -29.
S. London, S. Tomashevich. Handbook of high-frequency transformer devices. - M.: Radio and communication, 1984.

Author: I.Goncharenko (RC2AV); Publication: N. Bolshakov, rf.atnn.ru

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