High Power RF Amplifiers

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High Power RF Amplifiers

• By Nick Moldon G1BVI
• Eric Tucker G3TXZ
• November 1999

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High Power RF Amplifiers

• HF and VHF RF Amplifiers using old and new
  components
• What do YOU call High Power ??

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Types of Amplifier

• Ex PMR Amplifier Modules
• Power Modules
• Valves
• Bipolar Transistors
• MOSFETs

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Ex PMR Amplifiers

• Shown is a typical 15W Power Amplifier produced
  by PYE, for 70 MHz.
• Available for other VHF/UHF bands
• Note the Amplifiers may be identified by their
  part numbers.

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PYE Amplifiers

• PYE Amplifiers are small and compact.
• Ideal for adding on to your home built
  Transverter or FT290/690.
• Nominal 12 volt supply.
• Cheap.
• Very easy to use.

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Power Modules
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Power Modules

• Available for VHF and Up to Microwaves.
• Convenient and easy to use.
• Expensive New.
• Often found at Rallies.

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Valves

• Pros
• High Power output.
• Tuned o/p stage.
• Many parts found at Rallies.
• Parts are cheap.

• Cons
• High voltage supplies.
• Multiple supplies
• Tuned o/p stage
• Switched band tuning.
• Very Heavy
• A lot of chassis bashing

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Valves
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Other HV Bits and pieces
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6m 400W Valve Amplifier
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6m 400W Valve Amplifier
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6m 400W Valve Amplifier
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6m 400W Valve Amplifier

• Uses Twin 4CX250B Tubes.
• Air-tight Grid Compartment.
• Large Snail Type Blower.
• Integral LV and HV PSUs
• Large HV Components.
• VERY Heavy !!

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The 6m Beastie Mk1.
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Bipolar Transistors
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Bipolar Transistor Amplifiers

• Higher Power devices use up to 50 Volt Supply.
• Broadband designs easy.
• Must have Low Pass Filter at o/p.
• Need LARGE Heat sinks/Fans
• Highest power circa 150 Watts per device.
• Difficult to combine for increased power

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Bipolar Transistor Amplifiers

• Why are 50 Volt Supplies used ?
• Why is Filtering required ?
• Why LARGE sinks and fans ?
• What limits the Frequency range ?
• What Precautions should be taken ?
• Why difficult to combine ?

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250 W HF Bipolar Amplifier
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250 W HF Bipolar Amplifier
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MOSFET Amplifiers

• Up to 50V supply
• Broadband designs easy
• MUST have LPF at o/p
• Need LARGE heatsinks/fans
• Highest power circa 600W per device!!
• Easy to combine for increased power

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MOSFET Amplifiers

• Why are 50 Volt Supplies used ?
• Why is Filtering required ?
• Why LARGE sinks and fans ?
• What limits the Frequency range ?
• What Precautions should be taken ?
• Why easy to combine ?

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Erics HF MOSFET beast
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Erics HF MOSFET beast
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Nicks HF/VHF 1kW Monster
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Nicks HF/VHF 1kW Monster
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Nicks HF/VHF 1kW Monster
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The end