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Simple 400 Watt
RF Amp for
80 meters

VFO for 160 & 80 meters

Pulse Width Modulator and power supply

24 MOSFET RF Amplifier - Step by Step

Analog Modulator (Class H) and power supply

Class E Kits
and Parts


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This is a 24 MOSFET Class E RF Amplifier, covering the 80 and 160 meter amateur radio bands.

The amplifier is constructed in 4 6-MOSFET modules and uses IXDD414 digital gate drivers. Each gate driver drives 2 MOSFETs.

A single 1500pF multilayer ceramic capacitor is used per module as the shunt capacitor when operaing on 80 meters. An additional 1500pF capacitor is switched in (using small relays) when operating on the 160 meter band.

2 coils are used, one for 80 meters and an additional coil for 160 meters, which is shorted out by a relay when operating on 80 meters.

The tuning capacitor has sufficient range to cover both bands. 2 loading capacitors are used to provide sufficient capacitance for 160 meters. A fixed capacitor could also be used, if the device can handle the high RF current.

Schematics:


Pictures of the various construction steps for the 24 MOSFET RF Amplifier

Click on any picture to see a bigger image.

The Beginning Phases of Construction

step1.jpg (132330 bytes)
Heat sink drilled with some parts mounted.

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The source bus ready to be soldered to the MOSFET sources.

step3.jpg (109692 bytes)
Good closeup of a module showing the drain bus and shunt capacitor.

step4.jpg (146694 bytes)
The drivers are mounted, ready to be soldered.

step5.jpg (160249 bytes)
Drivers soldered to gate pins, driver bypass caps, drain transzorbs.

Further into the construction

step6.jpg (109909 bytes)
Closeup of the drivers, terminating resistors and connections to the driver input pins.

step7.jpg (68288 bytes)
Starting the output transformers (1:1 ratio).

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The secondary winding is run through the cores first.

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The primary windows are cut and bent. They should all be exactly the same.

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The primary windows are inserted into the cores to form transformers.

step11.jpg (165311 bytes)
A good shot showing all of the transformer connections. It is very important for the transformers to be connected properly to ensure proper combination of the class E modules. NOTE: This shows a "driver bus". Do not build it this way. I found that the unshielded bus gives rise to parasitics. Use an individual shielded cable to each driver with a termination. Check the other steps for a good picture of this.

Finally Assembly and Completion

step11a.jpg (158960 bytes)
Closeup showing the 160 meter shunt capacitor bandswitch relays. An additional 1500pF of shunt capacitance is switched in via the relays when operating on 160 meters. The shunt capacitors are soldered directly to the relays, and the relays are soldered to the drain bus through a piece of copper. This is done to minimize the inductance in the shunt capacitor path to ground.

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Each module has its own 12V switching regulator for the drivers.

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The underside showing the driver power supply transformers.

topview.jpg (138198 bytes)
View of the RF deck from the top. The 160 meter coil is to the right, and the 160 meter coil relay is visible just underneath the 160 meter coil.

finished.jpg (183222 bytes)
Another view of the completed RF deck. The variable capacitor to the far right is an additional loading capacitor in parallel with the main loading capacitor.