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Amplifier_Roi-Et.php    6972 Bytes    03-06-2024 18:11:07

Shortwave Power Amplifier ’Roi-Et’

A Power Amplifier with the MRF-101.

The Prototype. Not much inside ...

✈ Hardware Description • Notes

This design originally is from Jim Veatch, WA2EUJ. As the availability of RF-Transistors in the low budget and high frequency range is from a narrowband nature, we followed his idea and tweaked only here and there a little.

The Amplifier uses a N-Channel Enhancement-Mode Lateral MOSFET (MRF-101BN) in a Class A (Single transistor conducts full cycle) configuration. The Operating Point was adjusted therefore, that a Bias Current of 99 mA was flowing. A Gate Voltage of approx. 2.61 V was necessary to achieve that.

The by far smartest choice was the use of the Wurth Common Mode Choke (3.3 µH 12 mΩ). This greatly simplifies construction, as no complicated transformers need to be made. By that, the circuit becomes highly reproduceable.

In order to sustain the high voltages (Supply : 50 V), the capacitors are rated 100 V or more.

The Gate-Bias uses a Pre-Regulator with a BCP56-10 and a Zenerdiode (15 V). The fine regulation is done by a standard 78L05 in a SO8 case.

All resistors a 1%, 1W e.g. CR2512FX1000ELF from Bourns. (Mouser)

This Amplifier performs best with a linear Power Supply. Switching Power Supplies from the land of the rising sun may create a comb of (unwanted) sidebands.

The final assembly. The heatsink has a 0.9 K/W which mayst get hot :-)

✈ Downloads

✈ Performance • Small Signal Gain

Output Power, Input was +19 dBm from the SMC100A.

Compression not clearly visible, but beyond + 47 dBm at the output. My Power Supply could only deliver 3 A, which were used at + 10 dBm at the input of the first amplifier. For this measurement, two were used in series.

✈ Share your thoughts

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t1 = 6586 d

t2 = 238 ms

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