LDMOS RF Power Amplifier 23cm 300 Watt

LDMOS RF Power Amplifier 23cm 300 Watt designed to work with 23cm band amateur radio transceivers.

LDMOS RF Power Amplifier 23cm 300 Watt assembly options:
– Stand alone controller design, controller in its own box, with connection cable to main PA box;
– Integrated controller design, controller integrated into main PA box.

First option allow you to install the controller in a ham shack and PA box closer to antenna.
Second option is for installing the PA on the operator desk. Amplifier controls should located near the operator.

Fully assembled PA contents:
– PA pallet with radiator and fans;
– Power supply unit, 28V, 600 Watt;
– PA controller (stand alone design with connection cable or integrated design);
– PA bypass relay.

LNA without bypass relay supplied separately, not included into fully assembled PA contents.

LDMOS RF Power Amplifier 23cm 300 Watt case dimensions: 87 x 279 x 305 mm. Material: aluminum. Weight: at about 6 kg (integrated controller design). Thermal conditions allow operation with WSJT cycles at an ambient temperature of no higher than 30 °C. Small dimensions and weight are convenient for working in EME expeditions.

LDMOS RF Power Amplifier 23cm 300 Watt appearance (integrated controller design) below.

Fully assembled LDMOS RF Power Amplifier 23cm 300 Watt can be equipped with:
– PA-23cm-2W-IN-300W-OUT-pallet with integrated driver, configured for Input TX power < 2 Watt;
– PA-23cm-12W-IN-300W-OUT-pallet without integrated driver, that requires Input TX power < 12 Watt.

PA pallet made from aluminum plate on a CNC milling machine. Transistors are mounted on copper insert by soldering. Connectors, installed on the PA body: RF connectors N-female or SMA-female at the input, N-female at the output, controller connector, feed-through capacitor for connecting 28V from power supply.

PA 23cm 300W pallet schematics with and without integrated driver below.

PA-23cm-12W-IN-300W-OUT-pallet schematics from 2020-05-18
PA-23cm-12W-IN-300W-OUT-pallet schematics from 2020-05-18
PA-23cm-2W-IN-300W-OUT-pallet schematics from 2020-05-18
PA-23cm-2W-IN-300W-OUT-pallet schematics from 2020-05-18

PA 23cm 300W pallet layout with and without integrated driver below.

PA-23cm-12W-IN-300W-OUT-pallet layout from 2020-05-18
PA-23cm-12W-IN-300W-OUT-pallet layout from 2020-05-18
PA-23cm-2W-IN-300W-OUT-pallet layout from 2020-05-18
PA-23cm-2W-IN-300W-OUT-pallet layout from 2020-05-18

Lets take a closer look on PA 23cm 300W pallet with integrated driver design. Driver made on MRF9045L transistor. The driver input provides att. up to 5 Watt. Input TX power can be in the range 0.3 – 5 Watt (default adjustment < 2 Watt). Terminal cascade made according to a balanced schema with Anaren XC1400P-03s power divider at the input and a combiner in the form of a microstrip square bridge at the output.

Bridge simulation results below.

The amplifier circuit contains microstrip matching circuits, bias voltage stabilizer with thermal compensation, transistor initial current potentiometers, directional couplers with detectors for measuring output power, SWR and bridge balance, voltage switch with current sensor, PTT control circuit, copper insert temperature sensor.

Amplifier board material: Rogers RO4350B, 0.03, 1oz with plating holes and mask.

All wires are laid under the board in channels, specially made by milling. The amplifier enclosure is fully shielded.

How to choose the right PA

To select the PA, the following issues must be resolved:

1. Place of installation of the PA – on the desktop or on the mast?
2. What is the output power of your transceiver / transverter?
3. PA controller will be used with PA-23cm-300-Watt-pallet or with your PA to any VHF / UHF / SHF band?
4. Degree of PA readiness for work?

The answer to these questions will allow you to choose a pallet with a driver ( Pin < 0.3 — 2 Watt) or without it (Pin < 10 Watt).

Need to keep in mind that at the PA input, power is less than the output transceiver by the amount of losses in the feeder.

To use the controller with your PA (any band), the PA must include direct and reflected wave sensors on its output, DS18B20 heatsink temperature sensor and current sensor. To control the fan speed, 24V fans are required.

We developed fully assembled PA-23cm-300-Watt-box, with power supply, bypass relay, controller (built into the main box or into a separate box, like in the PA-23cm-KIT variation, note preferred variation in assembly request).

Equipment for self-assembly:

1. PA-23cm-300-Watt-pallet, with integrated driver (Pin < 0.3 — 2 Watt) or without ( Pin < 10 Watt)
2. Heatsink with fans
3. PA-controller in the form of a Remote control or assembled boards for embedding in your case
4. Current sensor board (PA-23cm-300-Watt-pallet does not require a separate current sensor, since early 2020)
5. Cable between PA-controller and PA-23cm-300-Watt-pallet, up to 15 meters max (5 meters default length)
6. Driver PA-23cm with power divider and combiner for combining of 2 x PA-23cm-300-Watt-pallet (600 Watt).

To find the optimal solution, answers to the questions above – required.

Place the answers to the ‘Additional notes’ section during submitting the assembly request:

PA controller

PA controller main functions:

  • measuring and displaying SWR, output power, current consumption values;
  • temperature and fan control through PWM;
  • built-in digital sequencer (that control all elements of the circuit, including the transceiver);
  • sound and LED indication of warning of excess of temperature and SWR;
  • over temperature and SWR protection;
  • settings saving in non-volatile memory;
  • the ability to configure the analog part of the device without SWR meter with only power meter available;
  • flexible adjustment of the device operating parameters to fit your needs as well as updating the firmware using PC software.

More information about the controller (read PDF documentation before use):

PA controller can be used with any VHF-SHF power amplifier. PA should contain SWR sensors in the load, temperature sensor. If controller supplied separately from the pallet, its package contains the ACS712 current sensor board. The pallet PA 23cm 300 Watt has current sensor inside (since early 2020) – external current sensor board is not required.

PA 23cm 300W KIT example
Connection cable variation 1
Connection cable variation 2

Connection diagram and cable pinout without current sensor board (Connection cable variation 1 appearance) below.

Connection diagram and cable pinout with the ACS712 current sensor board (Connection cable variation 2 appearance) below.

If PA output power is not enough for your application, you can use High-power-23cm-combiner in order to combine the power of a few pallets. Divider solution in development.

For PA based on 2 x pallets, with a output power of 600 Watts, we developed a power divider and combiner.

PA combiner SWR measurements

High Power 23cm combiner schematics from 2020-10-16

N2QG project based on 2 x PA 23cm DIY kit:

High-power-23cm-combiner appearance below.

PA-23cm-300W-heatsink appearance below.

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