600 Watt HF Amplifier
- There's an old axiom in amateur radio which states "Life's too short for QRP." While I generally disagree, it certainly appears to be true for 75m AM operation here in central North America, where a one watt carrier can quickly become buried in QRN & QRM. This amplifier is a mate for the QRP 75m AM Transceiver described elsewhere at this site.
- The amplifier uses four Motorola MRF150 50 volt TMOS power FETs configured in push - pull/parallel and biased for class AB linear operation. This scheme yields a power gain of 20db. The 1 watt drive from the "Wheat Box" will produce a 100 watt carrier (400 watts PEP @100% modulation) with headroom to spare.
- There's little original design here.
The basic 2 ⇒ 30MHz PA brick is straight from Motorola's application note EB104. The power supply, low-pass output filter, control circuitry and instrumentation are mine. Still, I would describe this project as mostly an exercise in packaging.
Some Amplifier Highlights
- Mode of operation − Class AB linear
- Output power − 600 watts PEP into 50Ω load
- Maximum drive power − 6 watts PEP into 50Ω input impedance
- Undesired output energy − at least −50dbc
- Power Source − 120v 60∿ nominal
- Front panel controls
- AC Power
- Mode Switch
- 20 DB − full output
- 14 DB − Via a 6db pad at brick input to produce 100 watts PEP for driving a legal limit amplifier
- Illuminated metering, left to right:
- PA current − 15A full scale
- Relative RF output
- Rear panel connections
- SO239 RF input connector
- SO239 RF output connector
- BNC connector − sample of RF output to monitor oscilloscope
- RCA connector for T/R control input signal
- AC Line cord
- Fuse access (10A SB)
- Size − 16¾"W x 8¾"Hx 12¼"D
- Weight − 43 lbs.
The EB104 Circuit Board
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