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ANTENTOP- 02- 2003, # 003

Old computer's PSU

 

Where:

 

P1- a dissipated power by the load,

P2 - a consumed power by the transformer.

 

P1 and P2 are equal:

 

P1 = I2R,

 

P2 = It2Rt,

 

 

Where:

I - a current going to transformer load,

It - a current going to the transformer from a transmitter,

R- the transformer's load resistance,

Rt- an input resistance of the transformer.

Here P is in watts, V, I, R are in volts, amperes and ohms.

 

Finding the efficiency by means of metering of RF currents

 

 

A transformer load resistance is known. Transformer's input resistance was early obtained by the circuit shown in Fig. 13. Thereby it is easy to find the efficiency. Note: The efficiency of the transformer was defined when a RF power of 10 watts gone to the transformer.

 

Instead of this it is possible to use another method.

 

Fixing of the efficiency with the help of RF- voltmeters

 

It is very easy to find the efficiency using the circuit shown on Fig. 14. However, RF ammeters are not widely used in a ham practice, on other hand RF voltmeters are common used devices. As result of this many hams would prefer to find the efficiency using only RF voltmeters. The “voltage” method is shown in Fig. 15. I used several RF voltmeters for my experimenters. One RF voltmeter was a commercial made Russian RF voltmeter, model VK-7 -4. Others voltmeters were home made, the reference [1] shows its circuits. I used a commercial made Russian oscilloscope model N-3015 like an RF voltmeter for several experimenters. Remember an oscilloscope shows a peak to peak (p-p) value of RF voltage, the RF Vrms (root means square) is root square from V p-p. Certainly, usually an oscilloscope has much

more metering error then a good RF voltmeter.

 

It is possible to find the efficiency of the RF transformer when both RF voltages, one at a transformer load another at the primary winding, are fixed. The efficiency (Eff) is equal:

 

Eff = P1/P2,

 

Where:

 

P1- a dissipated power by the load,

P2 - a consumed power by the transformer.

 

 

P1 and P2 are equal:

 

P1 = V12/R;

 

P2 = V22/Rt,

Where:

 

V1- an RF voltage across a transformer load,

V2- an RF voltage across the primary winding of an RF transformer,

Rt- an input resistance of an RF transformer,

R- a resistance of a transformer load.

 

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