ANTENTOP- 02- 2003, # 003

Old computer's PSU

The efficiency vs. frequency

On ranges of 160 -80 meters it is possible to use the autotransformer only for a reception mode with the transformer loaded to 450 or 600 Ohms and its primary winding is connected to a 75-Ohm coaxial cable. On ranges of 160 -40 meters it is possible to use the autotransformer only for a reception mode with the transformer loaded to 300 Ohms and its primary winding is connected to a 50-Ohm coaxial cable.

Note: Do not use the transformer without a load! It causes a high VSWR and damage to the transformer. If the transformer is used outside it should be protected against atmospheric influences. It is possible to use an egg from a sweet surprise "Chupa - Chups" for such a protection.

One more application - An RF ammeter

I found one more useful application for AT-33T transformer. This one was turned to a current transform for an RF ammeter. You need to add only a current loop to AT-33T transformer and this one will be a current transformer for an RF ammeter. The current loop (or a current winding) contains only one turn of a wire placed on a cheek of transformer's core (see Fig. 6). There was used a copper wire of 0.8 mm in diameter/# 20 AWG.

Current loop on the transformer side

I found that the 24 volt winding (Fig. 7A) as well as the inverter's winding (Fig. 7B) works as well as the meter's winding. A germanium diode was used in an RF detector at the meter's winding. A d.c. meter had a 1mA full scale deflection and 140-Ohm resistance. To verify the work of the RF ammeter made on the base of AT-33T transformer I connected it in serial with a control ammeter. Fig. 8 shows the circuit. Note: A control ammeter was a home brew RF ammeter designed by the reference [1]. The RF ammeter was calibrated with the help of a standard measuring equipment.

Tab. 4 contains testing data for the RF ammeter shown in Fig. 8. Using data from Tab. 4 I made diagrams "meter reading vs. frequency" to the 24 volt winding and to the inverter's winding (see Fig. 9 ). The curve shows that the inverter's winding (A- B) is the optimal winding for application in the RF ammeter made on the base of AT-33T transformer.

Current loop on the transformer side

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