Where:
P_{1}
a dissipated power by the load,
P_{2}
 a consumed power by the transformer.
P1 and P2 are equal:
P_{1}
= I^{2}R,
P_{2}
= It^{2}Rt,

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.

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 VK7 4. Others voltmeters were home made,
the reference [1] shows its circuits. I used a commercial made
Russian oscilloscope model N3015 like an RF voltmeter for several
experimenters. Remember an oscilloscope shows a peak to peak (pp)
value of RF voltage, the RF Vrms (root means square) is root square
from V pp. 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
= P_{1}/P_{2},
Where:
P_{1}
a dissipated power by the load,
P_{2}
 a consumed power by the transformer.
P_{1}
and P_{2} are equal:
P_{1}
= V_{1}^{2}/R;
P_{2}
= V_{2}^{2}/Rt,
Where:
V_{1
} an RF voltage across a transformer load,
V_{2}
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.
