The RF Power Devices in the IC-7800 Transmitter

Contributed by SergioCartoceti, IK4AUY

The IC-7800 200W Board.
The IC-7800 200W PA Board.

 

Device data:

Download a Zip file, containingthe PDF data sheets for the RF power devices in the IC7800 transmitter RF output chain.I took the device type numbers off the IC-7800 schematics (downloadable here).The devices are as follows:

  1. Mitsubishi RD01MUS1 1W MOSFET:  pre-predriver

  2. ST PD55003 RF MOSFET: predriver

  3. ST SD2918 30W MOSFET: driver

  4. ST SD2931 150W MOSFET: final PA (push-pull)

Some personal notes:

I believe that these MOSFETs should be excellent and very rugged in thisapplication (the ST SD2931 is rated at 292W power dissipation for each finalMOSFET device).  

These are recent device types with very low output capacitance and very low reverse capacitance (Crss) value.The lowest possible Crss is desirable for stable operation, and Crssis even lower than in the  MRF150 manufactured by Motorola and MA/COM. (The MRF150 is also a 50V RF MOSFET used in theIC-7700transceiver, the Yaesu Quadra amplifierand the Icom IC-PW1amplifier.) 

It is regrettable that the ST data sheet does not include a 2- tone 3rd-order IMD RF test at some biaslevel. The MRF150 data sheet includesIMD3/5 vs. Po curves. 

The Yaesu Quadra specificationsindicate 2-tone IMD3 < -30 dBc @ 1 kW PEP output. The IcomIC-PW1 page shows a 2-tone IMD3 plot for 1 kW PEP output at 7 MHz.

Visit Sergio's website. Read his article on MOSFET vs. BJT at RF.

Copyright 2004-2012 S. Cartoceti. All rights reserved.  Last revised: September 25, 2019.

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