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A power amplifier equipped with two TPM 2026-14 power FETs delivers an output power of at least 40 W on 2.3 GHz. The gain is about 13 dB.
Power Amp MT13-D-44
Description
Two TPM2026-14 Fets are combined via branch line couplers. An output power of 40 W can be achieved at a gain of 13 dB. The Fets used should be preferably from the same lot.
Construction
First cut holes for the Fets and the regulator into the PTFE board with a scalpel. Put board into the machined box and fasten those 16 brass screws. Be careful that holes in the PCB fit to the nuts in the box and have a bigger size - at least 0.3 mm. This is to avoid short circuits. Mount N-connectors. Mount regulators with an insulating sheet. Solder all resistors, caps and the feed throughs. Tantalum elcos have the positive polarity on the side with the bar!!!. Mount the box on a heat sink with maximum thermal resistance of 0.4K/W.
Check everything visually and with an ohmmeter. Connect B+ and measure 10.6 V at Pin 2 of the regulators. Set bias pots to maximum negative voltage of 3.2 V at the gate terminals.
Put a 39 Ω resistor from Pin 5/7660 to ground. This disables the negative supply. Check, that safety circuit let the output voltage drop from 10.6 V to 1.2 V.
If everything works ok, mount the power Fets carefully. The legs are cut to half the length. Use at least solder as possible.
Inspect everything again, clean the whole PCB.
Fig. 1: Circuit Diagram
Fig. 2: Parts Layout
Fig. 3: Pout vs. Pin
Fig. 4: Monitor Voltage vs. Pout
Alignment
Connect a dummy load of at least 50 W power capacity and a power meter to the output. Connect B+ to a current limiting power supply - overload trip should be set to 12 A - and adjust bias current of the FETs to 3.7A each. Across R10 and R13 you can measure a voltage drop of 0.17 V.
Then drive the unit with about 500 mW from a transverter. Check output power at about 14 dB gain. It should read about 12 W.
Then increase drive while observing the output power. An output power of 40 W should be reached with 1.6 to 2 W of drive. Don't use more drive power than 2 W.
If you are tough enough and have the money for spare FETs, you can even try to tune. This is accomplished by the attachment of small tuning stubs made from 0.1mm thick copper. These stubs can applied at gate and drain of the power FETs and possibly at the branch line couplers. If you have already more than 36 W of output power without tuning you probably should forget about tuning.
| Devices | TPM2026-14 |
| Supply Voltage | 12 - 15 V |
| DC-Current | 9.5 A |
| Gain | 13 dB |
| Output Power | > 40 W |
Parts
Ready made units, kits and parts can be ordered from Philip Prinz, DL2AM, Riedweg 12, D-88299 Leutkirch 3.
DL2AM, Philipp Prinz.