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ANTENTOP- 02- 2003, # 003

Old computer's PSU


Conclusion: It is possible to use AT-33T transformer in design of an RF ammeter. However, large dimensions of AT-33T transformer and the limited frequency range of an RF ammeter made on its base is the drawback of its application.


If you want the RF ammeter to work linearly on 160 - 30 meters use circuits given in Fig. 11-12. The drawback of these circuits is that

an expensive d.c. micro - ammeter of a 100μA full- scale deflection is used there.


If you need an RF ammeter for only one amateur range of 160, 80 or 40 meters, or you do not need linearity from your RF ammeter while this one is working on these ranges, use the circuit given in Fig. 7. In this case an inexpensive micro-ammeter with a 1000 micro Amper full- scale deflection will do well.





or several words about my researches of the AT-33T- transformer. Researches the opportunity.

Fig. 13 3 shows the measurement circuit for researches the opportunity. The primary

winding (A - B in Fig. 3) was loaded to 300, 450, 600 Ohms. Using different ways the secondary winding (C- G in Fig. 13) was connected to my home brew RF-bridge (this one was described in the reference [1]). My transceiver K-116 fed the RF-bridge. I made a lot of experiments and a lot of data for using of the ATX-33T by way of an RF transformer were obtained. Most interesting data will show below.


Measurement circuit


Efficiency is the first


However, what about an RF transformer has own input resistance close to 50 Ohms, when it loaded to 300-600 Ohms? It cannot serve as a final confirmation about its suitability for transfer an RF energy. Any RF transformer should have a good efficiency. Efficiency (Eff) is relation of a power, which transformer's load is dissipated (P1), to a power going from a transmitter to the transformer (P2). We can write the formula as:


Eff = P1/P2,

Thus I took an important attention to measuring of the efficiency. I used only one circuit (see Fig. 13) for measurement of an input resistance, but I used three different circuits for metering of the efficiency! Each of the circuits gave own metering error, and demanded

specific measuring devices. I want to write about all of the three circuits, because, they can be useful to hams who wants to do own experiments with other types of PSU transformers.


Fixing of the efficiency with the help of RF- ammeters


Fig. 14 shows very obvious and simple circuit for "current" method of measurement of the efficiency. Both RF currents, going to the transformer and to the load, were metered. I metered the RF currents by self-made RF ammeters (the RF ammeters were described in reference [1], pp. 21-22, 27- 31). When the RF currents are fixed, it is possible to find the efficiency of the RF transformer. The efficiency (Eff) is equal:

Eff = P1/P2,

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