The RF part of TR-9 uses an Si4463 chip (+20dBm output) along with a power amplifier based on AFT05MS004NT1 MOSFET (about 20dB of gain). When we are going to use the ADF7021 instead, the output level of it (+13dBm) won’t be enough to drive the PA. What I suggest is to use a MMIC like this one before the output stage:
https://uk.farnell.com/nxp/bga6589-135/mmic-wideband-amp-100mhz-3ghz/dp/2400497
What’s the goal for total power output? Duty cycle? How fancy do we want to get? 4 Watts/36 dBm seems like a decent goal, I don’t think it’s a terrible idea to add an RF power detector to the output that will a) give you a way to precisely servo the power output and b) detect high SWR and shut down.
The goal is 3…5 watts, 36dBm is a nice value. We will add automatic power control in version 1.3 of the board.
Important parameters that should be considered for the RF Power Amplifier are:
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Output Power
3-5 Watts / 33-37 dBm? -
Gain
This depends mostly on what the ADF7041 can supply - 0dBm? So maybe gain needs to be around 37dB? -
Linearity
4FSK is a Constant Envelope Modulation, so this means that the amplifier does not have to be incredibly linear. Essentially, the modulation can withstand some compression. -
Stability - SWR and Temperature compensation.
ALC circuitry can be used to shut down the amplifier under high SWR or high temperature conditions. -
Technology
Discrete MOSFET or all-in one module?
Toshiba, Mitsubishi and Motorola make modules that can produce good amounts of power on UHF that will fit this application. Mitsubishi RA07H4047M?
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DC supply voltage
Is the TR-9 a mobile or handheld? -
Regulatory - FCC Part 97, part 90?
Spectral Emissions Mask
Harmonics - 5th order Chebychev low pass filter?
–Konrad, WA4OSH/7
Output power: 1W on low setting, 3 to 5W on high
Gain: ADF can supply 13dBm. See diagram below.
Linearity: we don’t care about linearity. You got it right.
Stability, technology: See diagram below.
Supply: 7.4V from Li-Ion.
Regulatory: glad to be in a place, where we don’t have to care about FCC hehe. We are going to measure that. We use a basic LC pi-topology filter, see the schematic for details.