Modern equipment uses broadband transformers on long lines (TDF). In Amateur literature [1] describes only the TDF with integer coefficients of transformation of voltages nu=1,2,..., respectively, with the ratio of the resistances of ni=nu=1,4,9... . However, there is often a need to have PI=2. The following describes TDF with fractional ni=3/2 and ni=2,25 [2].

TDF consists of three lines W1 - W3 with the same wave resistance R and length l (Fig. 1). With increasing side of the line W2, W3 are connected in parallel so that the resistance between pins 3' - 4' is R/2, and consistently with them - the line W1 with resistance R so that the resistance between pins 1' - 4' is Rвых=1,5 p. Down side of the line W2, W3 are connected in series, and the line W1 - parallel so that the resistance of Meade conclusions 1 and 2 is determined by the parallel connection of 'p(W1) and 2p(W2, W3) and is Rin=0,66 R. In this case n1=Rвых/Rin=2,25.

Broadband transformer with a conversion ratio of 3/2

The analysis of low-frequency equivalent circuit shows that the common-mode voltage on the lines W1, W2, equal in magnitude and opposite phase, and W3 is equal to zero. That is, when execution of TDF on the same magnetic core W1 and W2 must have the same number of turns and the opposite direction of winding, and W3 is located outside the magnetic core and have the same length as W1, W2.


In Fig. 2 shows a circuit diagram of TDF. Line W3 has no common-mode voltage and only compensates for the phase shift introduced by W1, W2, therefore, if the line length is less than l/8 of the wavelength and does not require very high bandwidth (no more than two or three octaves), then W3 can be replaced by jumpers (Fig.3).


The calculation of the number of turns and the type of magnetic circuit may be the technique [1].

Possible applications of TDF, made in accordance with Fig.3, for approval of antenna shown in the table.


Rвых (Ω)


Rin (Ohm)






The GP agreement, or hb9cv please with 75 Ohm connectors





Approval of a frame with a perimeter equal to the wavelength and height of the suspension with the cable 50 Ohm



37.5 two lines of 75 Ohms in parallel


Approval 2 - 3 element YAGI with cable 50 Ohm

TDF 1,3 wound on the magnetic core 100 NN CHH, and have two windings 13 turns, bandwidth 10 - 30 MHz. TDF 1 coiled cable 50 Ohm 3 TDF in two parallel-connected cable 75 Ohm. TDF 2 has a bandwidth of 7 to 30 MHz and is made on the yoke 50 LN CHH in two windings of 15 turns of cable 75 Ohm. All three of TDF is designed for a capacity of 200 watts.


  • V. Zakharov. Matching device on the ferrite cores. Radio 1987. No. 6, p. 26 -29.
  • S. London, S. Tomašević. Handbook of high-frequency transformer devices. - M.: Radio and communication, 1984.
  • Author: I. Goncharenko (RC2AV); Publication: N. Bolshakov,

    Add comment


    Service manuals

    Copyright © 2020 Electrical circuits.