Keywords: 40 watt frequency modulation (FM) broadcast amplifier
40 watt frequency modulation (FM) broadcast amplifier
Circuit diagram
Indicators and features of the circuit:
Component list
serial number
Component parameters and description
FEC model (Note 1)
quantity
C1, C2, C4
5.5 - 50P small porcelain micromotact capacitor
148-161
3
C3
100P 50V ceramic capacitor (NP0)
896-457
1
C5, C6, C7
100N 50V porcelain card capacitor (X7R)
146-227
3
C8
100U 35V electrolytic capacitance
667-419
1
C9
500P 500V high frequency capacitor (METAL CLAD Note 2)
Be
1
C10
1N Threading Capacitor
149-150
1
C11
16 - 100P mica fine-tuning capacitor (Arco 424)
Be
1
C12
25 - 150P mica fine-tuning capacitor (Arco 423 or Sprague GMA30300)
Be
1
C13
300P 500V high frequency capacitor (Metal Clad Note 2)
Be
1
C14, C17
25P 500V high frequency capacitor (METAL CLAD Note 2)
Be
2
C15, C16
50P 500V high frequency capacitor (Metal Clad Note 2)
Be
2
C18
100N 200V porcelain card capacitor
Be
1
L1
64nH inductance with diameter 1.2mm enameled wire, a hollow coil, 6.5mm 4 turns to 8mm
Be
1
L2
25nH inductance with diameter 1.2mm enamel coated hollow coil diameter 6.5mm 2 turns to long 4mm
Be
1
L3
With a diameter of 0.7mm in a diameter of 0.7mm on a 6-hole magnetic bead.
219-850
1
L4
210NH inductance with diameter 1.2mm enameled wire, a hollow coil, a diameter of 6.5mm 8 turns, about 12 mm
Be
1
L5
21NH inductor with a diameter of 0.8mm enameled wire, a hollow coil, a diameter of 4mm 3 turns to 10mm
Be
1
L6
41NH inductance with a diameter of 0.8mm enameled wire, a hollow coil, a diameter of 4mm 4 turns to 6mm
Be
1
L7
C10 set in two magnetic beads on the power lead
242-500
2
L8, L10
100NH inductance with diameter 1.2mm enameled wire, a hollow coil, a diameter of 6.5mm 5 turns to 8mm
Be
2
L9
115NH inductance with diameter 1.2mm enameled wire, a hollow coil, a diameter of 6.5mm 6 turns to 12mm
Be
1
R1
10K 0.5W adjustable resistance (potentiometer)
108-566
1
R2
1.8K 0.5W metal film resistance
333-864
1
R3
33R 0.5W metal film resistance
333-440
1
D1, D2
BZX79C5V6 5.6V 400MW regulated diode
931-779
2
TR1
MRF171A (Motorola) RF power MOSFET
Be
1
SK1
BNC socket
583-509
1
SK2
BNC or N-type socket
310-025
1
Be
Be
Be
Be
Be
16 x 60 x 89mm 3.4 ° C / W radiator and fan
170-088
1
Note:
The FEC model is for reference only. The Metal Clad High-frequency capacitor has a short-thickness lead. The inductor coil of the input circuit can be smaller, but in order to make it easy, the same large coil as the output circuit is used.
Amplifier photo
40W output power 88-108 MHz frequency range 20dB gain + 28V 3A DC power efficiency high (70%, MOSFET AB amplifier) Component less output low pass filter (LPF) assembly
Prepare a 100 x 85mm double-sided printed circuit board (PCB). Drill a hole that the FETFET power tube can pass through. Diamond 4-6 holes on the PCB to secure the PCB in the cast aluminum shield. Design of how to fix the heat sink and its fan. Set the power supply, input, and output on the aluminum shield box. Refer to the photo and circuit diagram Cut the weld area in the PCB. Most of the back and front of the PCB is a ground wire. Welding element. The output low-pass filter portion is separated from the amplified circuit portion with a copper plate (or printed circuit board). The function of outputting low pass filters: The filter is used to filter high-end harmonics to reduce interference caused by the near radio, which is equivalent to high power RF output. For example, assuming that the magnitude ratio of the three harmonics is -30 dB. When the amplifier is 1W, the harmonic power is 1MW, nothing; but when the amplifier is 40W, the harmonic power is 40MW, the interference is the problem. The harmonic suppression of this circuit is greater than 50 dB. If you don't involve interference, you may not have to output a low pass filter.
Debug
Offset adjustment:
The input is 50 ohmic resistance short circuit (note: This circuit is self-excited in the case where the input is not entered), adjusting all variable capacitance to the middle, and the R1 is adjusted to the voltage minimum. Connect + 28V power supply, at this time should be around 14 mA. Adjusting R1 makes the supply current of 115 mA. If you find that the current has increased a lot, the circuit self-excitation oscillation requires multiple shielding isolation.
Input and output match adjustment:
Recommended equipment: current limiting power supply (+ 28V, 3A) 50W VHF fake antenna load 500MW-1W FM transmitter RF 40DB attenuator RF power table RF spectrometer and network analyzer
If you have an RF spectrometer and a network analyzer, you can use these instruments to adjust. Do not tighten without these instruments; add 500 mW-1W radio frequency signals through the FM transmitter, and the output power is measured with an RF power table by a 40 dB attenuator. If you don't have a RF power table, simply use the right side of the detection circuit to measure the voltage of the monitoring point. Set the emission frequency of the transmitter, adjust the fine-tuning capacitance C1, C2, C4, C11, C12, so that the output power of the amplifier is maximum.
Our other product:
