Broadband RF Amplifier 100W for TV Transmitter

The TV rf power amplifier has been tuned under class-A small-signal conditions and characterised under large signal class-AB conditions from band IV - V in UHF. The amplifiers circuit of the input and output matching networks contain mixed microstrip-lumped elements networks to transform the terminal impedance levels to approx. 25 W balanced.

The remaining transformation to 50 W unbalanced is obtained by 1 : 2 balun transformers. The baluns B1 and B2 are 25 W semi-rigid coax cables with an electrical length of 45° at midband and a diameter of 1.8 mm, soldered over the whole length on top of microstrip lines. To keep the circuit in balance two stubs L1 and L8 with the same length have been added. For low frequency stability enhancement the input balun stubs are connected to the bias point by means of 1 W series resistors. Large capacitors (C4 and C11) are added at the biasing points to improve the amplifiers video response.(in datasheet)


Printed Circuit Board (PCB)
The printed-circuit board laminate utilised is PTFE-glass with an er = 2.55 and a thickness of 0.51 mm (20 mills).


A complete TV transmitter amplifier has been designed and characterised based on the BLV861, capable of operating in full band IV and V with flat gain and high output power in class-AB. BLV861 is able to generate 100 W CW power and a power gain compression below 1 dB in band IV and V. Overall gain of the amplifier is >8.5 dB and an efficiency of ± 55%. TV-measurements have been carried out showing a 1 dB compression point above 120 W PO, SYNC at VCE = 28 Vand 150 W at VCE = 32 V.

• Amplifier shows an agreed linearity performance in class AB operation both under two tone and three tone conditions.
• Biasing the amplifier at a VCE = 32 V results in a higher output peak sync power and a better linearity response.

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UHF TV RF Amplifier For TV Receiver

This circuit is designed to work at UHF frequencies in the range 450-800MHz. It has a gain of around 10dB and is suitable for boosting weak TV signals. This RF amplifier use transistor MPSH10 with 9 volt power supply.

The MPSH10 transistor used is available from Maplin Electronics order code CR01B. Alternatives that may be used instead are BF180 and BCY90. The tuned circuit comprising the 15nH inductor and 2.2pF capacitor resonate in the centre of the UHF band. The 2.2pF capacitor may be exchanged for a 4.7pF or a trimmer capacitor of 2-6pF to improve results. The approximate frequency response is shown below. N.B. This is a simulated response using the TINA program produced by using a swept 20uV input swept over the frequency range 400-800MHz. Output was measured into a 1k source and the frequency generator has a 75ohm impedance.


Construction
The coil is half a turn of 18-20 SWG copper wire bent around a half inch drill bit. This ensures a low Q and therefore broad tuning. High frequency work requires special construction techniques to avoid instability (unwanted oscillations) caused by feedback from output to input. Veroboard is not suitable for this project as the capacitance between tracks is around 0.2pF. A better approach is to use tag-strip or a PCB. The circuitry should be enclosed in a metal case and a screen made between input and output. As the transistor is used in common base mode,its low input impedance is a good match for 50-75 ohm coax cable, whilst at the same time providing full voltage gain to the upper frequency limit of the device. The 15nH inductor load, having almost a short circuit impedance at DC, has an impedance of 56ohms at 600MHz. This inductance and 2.2pF capacitor form a tank circuit at the transistors collector, providing maximum gain at resonance. Note however that the voltage gain will be reduced under load, when the circuit is connected to the input of a TV set or a very long piece of coaxial cable for example. Hence the simulated Tina plot.

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100W Broadband UHF TV Power Amplifier

The TV amplifier has been tuned under class-A small-signal conditions and characterised under large signal class-AB conditions from 470 - 860 MHz. (All Datasheets)

Schematic Circuit Amplifier
The total description of the amplifier is given in Figs 6 and 7 and Table 8 (in datasheet). The amplifiers input and output matching networks contain mixed microstrip-lumped elements networks to transform the terminal impedance levels to approx. 25 W balanced. The remaining transformation to 50 W unbalanced is obtained by 1 : 2 balun transformers. The baluns B1 and B2 are 25 W semi-rigid coax cables with an electrical length of 45° at midband and a diameter of 1.8 mm, soldered over the whole length on top of microstrip lines.

To keep the circuit in balance two stubs L1 and L8 with the same length have been added. For low frequency stability enhancement the input balun stubs are connected to the bias point by means of 1 W series resistors. Large capacitors (C4 and C11) are added at the biasing points to improve the amplifiers video response.


Printed Circuit Board (PCB)
The printed-circuit board laminate utilised is PTFE-glass with an er = 2.55 and a thickness of 0.51 mm (20 mills).


Component Mounted


A complete TV transmitter amplifier has been designed and characterised based on the BLV861, capable of operating in full band IV and V with flat gain and high output power in class-AB. BLV861 is able to generate 100 W CW power and a power gain compression below 1 dB in band IV and V. Overall gain of the amplifier is >8.5 dB and an efficiency of ± 55%. TV-measurements have been carried out showing a 1 dB compression point above 120 W PO, SYNC at VCE = 28 V
and 150 W at VCE = 32 V.

• Amplifier shows an agreed linearity performance in class AB operation both under two tone and three tone conditions
• Biasing the amplifier at a VCE = 32 V results in a higher output peak sync power and a better linearity response.

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14W UHF TV RF Amplifier 470-860 MHz

Working Frequency 470-860 Mhz UHF Band IV and V. Power out of the RF Amplifier about 14 Watts with power input 1.5 Watts.

( Transistor Datasheet)

Schematic

Part Lists:
C1 = C6 = C16 = 4,7 pF (500 V) multilayer ceramic chip capacitor
C2 = C3 = C20 = C21 = 33 pF multilayer ceramic chip capacitor
C4 = C9 = C13 = C19 = 1,2 to 3,5 pF film dielectric trimmer
C5 = C7 = C15 = C17 = 100 nF multilayer ceramic chip capacitor
C8 = C10 = C11 = C12 = 220 pF multilayer ceramic chip capacitor
C14 = C18 = 6,8 mF/40 V solid aluminium electrolytic capacitor
C22 = C23 = 1 pF (500 V) multilayer ceramic chip capacitor
L1 = L2 = L13 = L14 = Coax. 50 Ohm with diameter 2,2 mm; lenght 29,0 mm, soldered on striplines
75 W (1,1 mm ´ 28,0 mm). inner L1 dan L13 not connected
L3 = L4 = 52 W stripline (2,0 mm ´ 16,5 mm)
L5 = L8 = 470 nH microchoke
L6 = L7 = 39 W stripline (3,1 mm ´ 8,0 mm)
L9 = L12 = 1 Turn (1,0 mm); diameter 5,5 mm; lead space 2 ´ 3,5 mm
L10 = L11 = 39 W stripline (3,1 mm ´ 34,0 mm)
L3, L4, L6, L7, L10 dan L11 are striplines on PTFE fibre-glass PCB wirh dielectric (Îr = 2,74); w 1/32".
R1 = 10 W carbon resistor

BIAS CIRCUIT

Component Part List:
C1, C2, C4, C5, C6 = 1nF LCC Chip + 10nF LCC Chip
C3 = 100µF Sprague
C7 = 10µF Sprague
D1 = 1N 4001
L1, L2 = 5 Turns , Diameter 0.5 mm, W Diameter 3mm
P1 = 1k.
R1 = 56 ohm/ 1/2W
R2 = 5600 ohm, 1/2W
R3 = 2.2 ohm, 3W
R4, R5 = 56 ohm, 1W
R6 = 4,7 ohm, 1/2W
T1 : BDX 54 B/BD139

Component Layout


PCB Dimension 145,74 mm X 59,865 mm

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TV Linear Power Amplifier 470-860 MHz

The Wide-Band UHF Power Amplifier for TV Transposer band IV/V designed with transistor BLW32 and BLW33. In this case, my RF Amplifier design replaced them with 2 pieces BLW34 have good result.

RF Amplifier for 470-860 MHz taken from Philips Aplication Note (AN_BLW32_33). Please download file in PDF format.


For combine two BLW34 download file here

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