🔲The original version of my LF/MF MOSFET Class-E 🗼transmitter power amplifier design was described on 📅6 December 2015, with follow-ups on 📅9 January 2016 & 📅21 September 2017. It has been in regular use since then. However, several modifications have been made recently.
The ➰inductive reactance of the bias choke has been increased to the approximate optimal value of 30x MOSFET drain resistance, ( see Note below ), to improve the performance on the LF 📏2190m/∿136KHz band. So a second ⊚T200-26 core and a ⊚T157-52 core with 29 & 18 turn windings respectively have been added in series with the original ⊚T200-26 core; all are iron powder toroidal cores.
The ➿inductor in the original LF band module could become quite hot. Two replacement modules have been made; one is completely new and uses Litz wire for the ➿inductor, while the other is a redesign of the original still using 16 gauge enamelled copper wire (ecw), but changing capacitor values by "select-on-test". The coil-former for the 'ecw' ➿inductor was 3-D printed from PETG filament, and is partially ribbed along its length. The DC blocking capacitor has to be a low-loss type as the RF current through it can be considerable. Here, I have used several capacitors connected in parallel to share the current. The spacing between the ➿inductor and ground-plane has been increased to reduce losses. Both designs for the LF band module will be tested in turn for comparison.
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| Internal view cover removed - note toroids & LF band module with ecw coil |
Currently the output power is 210 watts on MF (📻📏630m/∿472KHz band ), 282 watts on LF (📻 📏2190m/∿136KHz band Litz wire coil in band module ) and 302 watts on LF ( 📻📏2190m/∿136KHz band 16-gauge ecw coil in band module ) - see image below.🔳
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| Oscilloscope display - (yellow) input voltage Vgs, (blue) output voltage Vo |
Note: for Class E, Drain Load Resistance = (Supply Volts)🠉2 / 1.2 x Output Power
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