Matching exponential transformer for satellite receivers. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Matching exponential transformer for satellite receivers. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Телевидение

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The input resistance of microwave bipolar transistors is a few ohms and has an inductive component. Therefore, when a coaxial cable with a wave impedance of 75 ohms is directly connected, a standing wave occurs in it.

If you have 10-20 cm of silver-plated coaxial cable with PTFE insulation, it is easy to make an exponential transformer from it. The insulation of such a cable is made of fluoroplastic ribbons wound around the central wire. It is necessary to remove the cable sheath and unwind the fluoroplastic ribbons (except for the last one). This insulation diameter will be at the output end of the transformer. Using a knife, cut the ribbons with a converging wedge. Wind the ribbons back, trying to get an exponential change in the diameter of the insulation section along the length. Not all ribbons are required! Stretch the braid and squeeze it tightly over the insulation. Lubricate the braid with LTI-120 flux and solder. The solder spreads superbly over silver. The resulting semi-rigid segment can be bent and even rolled into a ring. Subsequent measurements of several samples of the transformer showed that the accuracy of the exponent and the length of the cable are not critical. It is only necessary to achieve a monotonic decrease in the cross section. The resulting transformer is soldered between the input connector and the RF. receiver block.

Matching exponential transformer for satellite receivers

For different options for home-made h.h. blocks, an increase in gain of 4-6 dB was obtained! The CBV in the feeder has improved significantly, and I believe the noise of the input stage has decreased due to improved input matching over the entire frequency range. I think such a useful way to get additional gain on the microwave is applicable to many broadband devices.

Author: E.Shustikov, UO5OHX ex RO5OWG; Publication: shustikov.by.ru

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