Two New Transformers for Measurements on Balanced Systems

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SINGLli-tNDHD electronic measuring instruments such as electronic voltmeters, distortion meters and wave analyzers can be used quite successfully to make measurements on balanced systems by introducing a high-performance transformer between the balanced system and the single-ended instrument. To enable single-ended -bp- instruments to be used in such applications, two new halanced transformers have been designed. One is especially useful in carrier-communications work and operates over a range from 5 kc to 600 kc at a maximum level of +22 dbm. The second is designed for audio work and operates from 20 cps to 45 kc at levels up to +15 dbm,

A schematic diagram of the 5 kc to 600 kc transformer is shown in Tig, 3. The switch shown in the diagram is built into the transformer ease at are the resistances in the secondary circuit. The transformer is designed for use with either 135- or 600-ohm systems and can be made to have an input impedance of 135,

Fig. 1. -hp- AC-60A Matching Transformer is designed for carrier work, operates from 5 kc to 600 kc.
Audio Bridging Transformer
Fig, 2. -hp- AC-60H Bridging Transformer is designed for audio applications from 20 cps to 4S be.






Fig, J. Schematic diagram of -hp- AC-60A.


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Fig, J. Schematic diagram of -hp- AC-60A.

600, 2250, or 10,000 ohms as desired. It can thus be used either as a terminating or bridging device as required by the application. Typical arrangements are shown in Fig. 4.

The transformer can also be used with the -bp- Model 20UCD 5 cps to 600 kc 1 watt test oscillator in combination with an -bp- 400 series vcvm to form an accurate signal generator for balanced system work. An arrangement for this combination is shown in Fig. 5.

It is interesting to note that in the terminating arrangement of Fig. 4(a) and the signal generator arrangement of Fig. 5 the db calibrations on the -bp- 400 series voltmeters can be used to read the power level directly in dbm. This is true regardless of whether a 135- or 600-ohm circuit is used, provided the proper primary taps are used. This occurs because the voltmeter is always connected at a 600-ohm level and because the db

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Fig. 5, Connection of 5 kc-fiOO kc transformer for monitoring signal power.

calibrations on the voltmeter are referred to a 0 db value of 1 milliwatt in 600 ohms. In the bridging arrangement of Fig. 4(b) the dbm calibration of the voltmeter will also be valid if the proper primary taps are used, because the voltmeter sees an impedance of 600 ohms.

The second transformer, the -bp-AC-60B, has a circuit similar to the first but differs in that it has no 135-ohm input terminals. Otherwise the AC-60B can be used in the same manner as the AC-60A.

Fig. 4. Connection of transformer for term'n>,t<i*>g itid hri/lgittg applications.


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