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I'm designing a small UHF data transceiver for the 70cm band, based on a Silicon Labs EZRadioPro Si4463 IC. Modulation is FM, 12.5kHz channel step. The concept is similar to SiLabs' AN656 application note but with a different power amp BJT as the NESG270034 and NESG250134 are obsolete.

Design goal is 1W out (+30dBm) at 3V or 5V supply, from a +13dBm or +20dBm driver source. I figure that's about 17dB of gain. 500mW would also be passable.

I've been looking at alternatives to the RF BJT, and have hit a small problem. Many RF BJT manufacturers only provide component models for expensive commercial tools like Agilent ADS or Microwave Office. For instance, Infineon provide S2P models (which I understand are usable with RFsim99) for most of their parts, but NXP only seem to offer S2P data for their high-power (25W+) amplifiers and not for their discretes (except some discontinued ones like the BFG135).

Are there any free or low cost tools which can be used to design the matching networks for FM UHF power amplifiers using the ADS models?

I'd also be interested in hearing suggestions on other UHF PA transistors I should look at but I think that might be better suited to a separate question!

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    $\begingroup$ Hi philpem and welcome. $\endgroup$ – mike65535 Nov 7 '18 at 13:08
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ngspice is free and can read and write S2P models.

You can also just open the file with a text editor and read the S-parameters manually. With the appropriate skill and care, you can then manually calculate the desired matching with no electronics software at all.

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If you have a calculator that can do matrix math with the S-parameters, you can manually compute the required matching components for a given frequency. S-parameters are given over a wide frequency range for the part so the data can look intimidating, but really the worst thing you'll have to do is interpolate between two given frequency points to arrive at the S-parameters for your given frequency (which will be just one 2x2 matrix). Then you can easily use those to figure out how to match your system for best performance.

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