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The following describes the calculation method of the circuit elements of the P-loop, which is often used only in the terminal stages of radio transmitters (see figure).


The final stage of a radio transmitter

Dashed lines show parasitic capacitance C01 and C02, as well as the load resistance circuit Ra (the input impedance of the antenna-feeder system). When calculating the capacity CA and C01, CA and C02 combine, denoting: C1=Ca+C01;

C2=CA+C02 (assuming that the capacitance of the capacitor CP is high and its effect is neglected).

Initial data for calculation:

Frequency fо.

The resistance of the anode load of the lamp RA; it is determined in the calculation process of the lamp mode or take from the table the model selected lamp mode (see, e.g., [1], p. 236).

The load resistance circuit RA; it depends on the type and design of antenna-feeder system and good coordination of the feeder with an-tenou (SWR close to one) is equal to the characteristic impedance of the feeder.

The quality factor of the loaded circuit q e; most often suppose q e=10-20 (for higher frequencies take a smaller value).

K. p. D. circuits, which are set from total energy considerations, it is advisable to take n=0,8.

The parameter calculation circuit

For ease of calculation we introduce the auxiliary coefficient:

Calculate the magnitude of containers:

Then the equivalent capacitance of the circuit is determined by:

and the inductance of the coil

When all the calculations are the values: C in pF, fо in MHz, R in ohms, L is in µh.

Well-known formulas (see e.g. [2],p. 75) define the number of turns of the coil in terms of its dimensions.

In the opinion of defined value of parasitic capacities:

C01=swich+Sm+SDR+Scat+Sa chief and C02=Cm2+Stole+Sanac,

where: swich - output capacitance of the lamp,
Sm - capacity anode mounting parts schematic
Cm2 is the capacitance of the antenna mounting parts schematic
SDR - self capacitance of the inductor,
Scat - self-capacitance of the coil,
Stole - parasitic capacitance of the switch,
Sa start SA and initial - initial-capacity capacitors.

The value of swych find in reference books. Self-capacitance of coils and chokes define calculation (see 12],pp. 81-82) go by the measurements (on Q-meter or resonance method); initial capacitance and the parasitic capacitance of the switch is also better to measure.
Capacity of installation (Cm and Cm2) are typically set in the range of 5-20 pF depending on its execution.

Evaluation of the calculation results

It is necessary that the values of C1 and C2 were larger than the values C01 and C02, respectively. Sometimes, especially at high frequencies, it happens that C1<C01. This means that the circuit cannot be configured on a given frequency. In the atom case, it is necessary to take measures to increase C1 or decrease C01.

The capacitance C1 (for a given frequency fо) can be increased by increasing the q-factor of the P-loop or reduction of Ra. Improving the figure of merit in Amateur conditions hard to implement. Reduce Yes same can be achieved by using a different lamp, which in a typical mode requires less Yes, or changing the mode previously selected lamp, reducing Ua, and some increasing arousal.

The decrease C01 possibly due to the use of parts that have smaller parasitic capacitance, and to improve erection. However, the improvement of installation generally requires increasing the size of the final cascade..

After clarification of certain parameters again carry out the calculation in sequence.

The accuracy of the calculation greatly depends on how close to the real value taken as initial data for calculation.

When properly selected parameters of the P-loop mode cascade will be optimal. This is evidenced by the decrease in anode current of the lamp by 20-25% when configuring the circuit into resonance.

Literature

1. S. Bunimovich, L. Yailenko. "Technique Amateur single-sideband radio communications", ed. DOSAAF, 1964
2. "The radio Amateur's Handbook" edited by Vladimir Melnikov. Sverdlovsk publishing house, 1961

Author: L. Chernov (UA3SR), Ryazan, Russia; Publication: N. Bolshakov, rf.atnn.ru