1 Watt RF Power Amplifier for 1.5 GHz


This a simple 1 watt RF power amplifier project designed for use with a 1575.42 MHz (L1) GPS jammer source.

The amplifier is based around a Renesas/Hitachi PF08114B MOSFET power amplifier module which is normally intended for the E-GSM and DCS1800 (Europe/Asia/Middle East) cellular phone bands.  You can sometimes find the PF08114B on eBay, usually at a very low price.

The PF08114B is a dual-band amplifier (900/1800 MHz) and only one band can be activated at a time.  The wide RF bandwidth nature of the PF08114B means the DCS1800 amplifier portion is still very usable at the 1575.42 MHz L1 GPS frequency.

With a +10 dBm (10 mW) RF input, you can obtain around a +30 dBm (1 watt) RF output.  The PF08114B is designed to run at nominal +3.5 VDC and will draw a continuous 550 mA.  Running it at a slighty higher voltage of +4 to +5 VDC is possible to squeeze out a little more RF power, but be sure the device is properly heatsinked and matched to a 50 ohm load.

The PF08114B has three main DC power connections, Vdd, Vapc, and Vband.  The Vdd1 and Vdd2 are the main +3.5 VDC power connections, with the current draw on these two lines totaling around 550 mA.

The Vapc line acts as a RF power control line.  It's fixed at around 2.2 volts in this application and an experimental SWR protection circuit can pull this line "low" on detection of an output fault.  This essentially "powers down" the PF08114B, protecting it from overheating when no antenna (or load) is connected.  This line draws around 3 mA.

The Vband selects the operating band of the PF08114B.  When ground, the 900 MHz RF amplifier portion of the PF08114B is activated, when at around +2.0 volts, the 1800 MHz RF amplifier portion of the PF08114B is activated.  The current draw on this line is minimal.

Because of the PF08114B's surface-mount package, you'll need to do a little bit of hacking and tweaking if you want to homebrew your own PC board.

For this design, the PF08114B will be mounted upside down.  This will allow easy access to the solder pads normally on the bottom of the PF08114B, and it's metal case will now be a combination heatsink/ground.

You'll need to cutout and file a properly-sized rectangular hole in the PC board to fit the PF08114B.  Little pieces #30 gauge wire will connect the PF08114B pads to the PC board traces.

Pictures & Construction Notes

Overview of the Renesas/Hitachi PF08114B MOSFET RF power amplifier module.

They are available on eBay for around $4 each.

It's in a 10-pin surface-mount package.

Bottom view of the Renesas/Hitachi PF08114B MOSFET RF power amplifier module.

Making a proper PC board for this device would require alot of work, but we can improvise something cheaper by mounting the device upside down.

Making the PC board for the amplifier.

Proper microwave construction techniques will be required.  Use quality doubled-sided FR4 material with lots of vias connecting the ground planes.

The voltage regulator is a Micrel MIC29152BU configured for a +3.5 VDC output.  The R1 resistor is 2700 ohms (1%) and the R2 resistor is 1500 ohms (1%).  Refer to the MIC29152BU's datasheet for more information on tweaking the output voltage value.

Be sure the ferrite beads on the PF08114B's Vdd power lines are capable of handling 600+ mA without saturating or dropping too much voltage.

An experimental SWR protection circuit was added to this design, but it doesn't work quite like I wanted.

An Anaren 1A1305-20 20 dB directional coupler detects the reflected power and pulls the PF08114B's Vapc line down in a high SWR condition.  The 20 dB coupler doesn't quite have enough coupling power for this low-power amplifier.  A 6 dB (1A1305-6) or 10 dB (1A1305-10) coupler should be used instead.

Mounting the Renesas/Hitachi PF08114B MOSFET RF power amplifier module.

It's placed upside down into the cutout made in the PC board.

Solder-tin the PF08114B's (top) case and add little strips of thin copper foil to connect the PF08114B's case to the ground plane of the amplifier circuit board.  The thin copper foil can be found at most hobby stores.

Doing this helps to properly ground the PF08114B and also acts as a makeshift heatsink.

Finished overview of the PF08114B installed in the amplifier circuit board.

Be sure the bottom of the board is very smooth.  Use the side of the soldering iron to "smooth" out the solder.

Completed amplifier circuit board overview.

The RF input (1575.42 MHz / +10 dBm typical, +15 dBm maximum) is via that top trace.

The RF output (approximately +30 dBm) is via the bottom trace.

Small #30 gauge wire jumpers connect the PC board traces to the proper PF08114B pads.  Be sure to note "pin 1" when the PF08114B is upside down!

The SWR protection components where not installed yet, as this circuit was still experimental.

The detection diodes may need a little bit of forward bias, depending on which ones you use.  This can be done with a simple two resistor voltage divider at around 0.2 volts.

Mounting the 1 watt RF amplifier circuit board into the case from an old cellular phone (800 MHz) receive pre-amplifier.

SMA connector are used on the RF input/output.

You can power the RF amplifier from any +6 to +12 VDC power source capable of around 600 mA continuous.

Completed overview.

Be sure the case which you mount the circuit board to is capable of acting as a heatsink.

Two extra #2-56 screws were added off to the sides of the PF08114B.  These are to help ensure the PF08114B is properly heatsinked and grounded to the aluminum case.

Testing the RF amplifier at 1575.42 MHz with a 0 dBm (1 mW) RF input.

The reference line is 0 dBm at there is 30 dB of attenuation on the spectrum analyzer's input.

No oscillations or spurs were detected.

Completed case overview.


Datasheets & Notes

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