I continue to try different amplifiers in order to improve my station for weak signal digital modes, such as JT9 and WSPR, on the 475KHz, 630m band.
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| unboxed prototype amplifier with space left for antenna relay |
The amplifier posted here is a medium power, and physically small, two IRF640N mosfet class C design. I designed the amplifier so that the 13degC/W heatsinks would provide adequate cooling for up to 50 watts output power when run from a 54Vdc power supply, while still retaining the compact size. With 2.5W drive power at the input, I measured 33W output power, ( gain 11.2dB ). This was deliberate because at that power level, the optimum mosfet drain load is almost 50 Ohm; so I avoided the need for any output matching circuit. It will be interesting to see what I can achieve on digital modes now.
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antenna change-over circuit added (lower-right)
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Using it for the first time yesterday evening, my WSPR beacon transmission was received at a record distance 1655kms in France, and I was rewarded with a JT9 digital mode contact with Scotland at a similar distance.
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finished amplifier in home-made enclosure
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3 February 2023
I received a request from a radio amateur in the USA ( Jeff, callsign WB8RJY ) for the circuit diagram, as he wanted to construct the amplifier. A few days later Jeff sent me several pictures of his completed amplifier, and a summary of his WSPR activity using the amplifier detailing some very long distance reception reports.
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amplifier built by WB8RJY based on my design
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2 comments:
How do I get a schematic for this little amp showing values of resistors,capacitors etc? plus , toroid type and number of turns. I want to build one of these and experiment with it on 630m.
Hi Steve
Could you share the circuit and components of the 630m amplifier?
Best regards
Al, CX8AT
cx8at.eme@gmail.com
cx8at@adinet.com.uy
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