The PA can be reactive 1-2W ,88-108MHz FM Transmitter Power Extension For 10-15W, with single-tube amplification and multi-level Class C low-pass filter, has a high conversion efficiency and a strong Yi wave suppression.
See the circuit as shown in drawings, using high-power launch tube C1972, its parameters are as follows: 175MHz, 4A, 25W, power gain ≥ 8.5db, according to parameters shown, the circuit work center frequency of approximately 98MHZ, of approximately 2W of RF power input , the rated output of up 15W. To maintain its 88 ~ 108MHZ within any one frequency when the output of rating can be the center frequency of the previous level of some components to make appropriate adjustments. If necessary, can reduce the low-pass wave device series, in order to increase the output power. The expanded power of the signal from the three high order low-pass filter filtered Yi Bo fed into the transmitting antenna elements.
Component selection: In addition to electrolytic capacitors, the other tiles with high-frequency capacitors, C11, C12, C14 with high-frequency characteristics of a good, stable performance of the tunable capacitors, choke inductor RFC1, RFC2 by finished inductors, must pay attention to the current RFC2 carrying capacity, should be used with coarse diameter core of the inductors. L1-L6 are available ø0.8mm high-intensity enameled wire system, a diameter of 5MM, circle the number of the figure with "T" as the unit indicated. Q1 with ordinary Q9 socket, and supporting the use of plugs. Q2 with special radio-frequency output connector 50Ω, then solution resistance is smaller, more conducive to impedance matching. Power amplifier tubes exclusive launch of the more common tube C1972, of course, especially if you are silver sufficient to buy a piece C2538 high-gain tube, then power will be even greater.
Debug circuit, important to note that due to big power circuits must be connected to the pseudo-load (I use 30 1W, 1500Ω made of high-precision metal film resistors in parallel), and sufficient cooling device in the normal working hours Power does not less than 2.5A, the antenna impedance strictly equivalent to 50Ω, can not use short rod rod antenna, or a strong current of the RF feedback circuit will result in self-interference, most of the RF energy can not be convergent to the space consumed by the power tubes to overheat damage ; to be fired through the 50Ω coaxial power table onto a dedicated outdoor antenna. The circuit can work properly lies in circuit debugging, the whole process had to be very careful. Debugging, only a smaller incentive to enter the power supply voltage down to 9V, using high-frequency voltage meter (not an ordinary multimeter) to monitor high-frequency voltage across the load off, adjust C12, C14, L3, L4, L5, L6 , the voltage range up to 15-20V or so, and then adjust C11, L1 the voltage maximum. And then gradually increase the voltage each time voltage is repeatedly adjusted to improve C12, C14 and C11, L1 so that the output voltage is the highest, noted that the voltage should be synchronized with the RF input power increased incentive to ensure the accuracy of the results to debug. To achieve ratings, the power supply voltage of 13.8V about 2A current work around, 50Ω purely resistive voltage across the load off ≥ 40V, RF output power up to 15W.
50Ω RF power amplifiers using this umbrella with the omni-directional vertical antennas (gain of about 2dB), an ordinary FM radio testing, launch from the coverage of not less than 15K.
Our other product:
