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After several months of development, MDRF is pleased to offer this kit version of N6QW's P3ST SSB Transceiver for 15, 17, and 20 meters. Its modular construction allows for easy assembly, testing, and modification. Most of Pete's recent designs are intended as experimenter's platforms. Any of the modules that make up the P3ST's superhet SSB architecture can be swapped out for different designs or modifications. By the way, any of the modules can be used in other homebrew rigs as well, and they will be available for sale separately.
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Modules plug into headers on the motherboard which carry relay-switched power. Where possible, components are spaced apart as far as possible for ease of assembly by those who suffer from FFS (fat-finger syndrome). With a standard module size--2.5 x 1 inch (5 x 6.4 cm)--and connector spacing, it will be easy to swap them out or to modify them.
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A key feature of the P3ST is the reuse of circuit modules for both transmit and receive. The mixers, the IF module, the band-pass filter, and the RF amp are switched by relay from RX to TX with a signal from the push-to-talk line. Here is the rig's block diagram:
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Going clockwise around the block diagram, here are the modules:
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The microphone amplifier is a single 2N2222A transistor in common-emitter configuration with an input impedance of 1000Ω. A jumper block can engage DC bias power for electret microphones. Power in switched to the amp on TX.
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The audio output amplifier uses a 2N2222A as a preamp for an LM380 power amp IC capable of 1.5 Watts output. Volume is controlled by a panel-mounted potentiometer.
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The VFO (or "1st") mixer is identical for the BFO (balanced modulator/product detector): a Mini-Circuits ADE-1 double-balance diode-ring mixer IC with an LO drive of +7dBm. The mixers can be thought of as the rig's lungs: they breath in RF or audio signals and take them to the filters and amplifiers.
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If the mixers are P3ST's lungs, the IF module is its liver, filtering out everything but a 2700Hz-wide intermediate frequency. It is used on both transmit and receive. At each end of its QER filter, 2N2222A amplifiers contribute to the 100dB or so amplification needed to take either an antenna or microphone signal to their proper levels.
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The bandpass filter serves two functions: to reduce out-of-band signals coming in from the antenna, or to attenuate IF and other signals that leak past the VFO mixer on their way to the RF amp and driver/final amplifier. It is distinctive with its low-value "gimmick" coupling capacitor.
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Like all the other small-signal amplifiers in the P3ST, the steerable RF amplifier uses a single 2N2222A stage. Its purpose is to either amplify the signal coming in on the antenna or to act as a pre-driver for the driver/final amplifier. A relay activated by the PTT line "steers" the amp from one function to the other.
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The driver/final amplifier module is the muscle of the P3ST. It takes the filtered SSB signal from the RF amp pre-driver and boosts it up to near 5 Watts for QRP use or to drive an external amplifier. The driver is a 2N2219A transistor (with its crown heat sink) and the final amp is an IRF510 MOSFET. Test points and a bias potentiometer make optimum adjustment easy.
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The final low-pass filter removes the inevitable harmonics produced by the final amplifier to a level acceptable to other Hams and to the FCC. The component values for this filter have been calculated to serve the 15, 17, and 20 meter bands. The SSB signal's next stop in the antenna and the ionosphere.
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And finally, the beating heart of the P3ST: the digital VFO/BFO controller. The version pictured is interim. The version to be shipped will be on a different PC board. The controller uses the now-venerable combination of an Si5351 module controlled by Arduino software. In this case, however, the microcontroller module is a Seeed Studio Xiao with a Raspberry Pi RP2040 MCU. It will run any program intended for an Arduino (including the Si5351 and other libraries) or it can be programmed in MicroPython or Circuit Python. Digital connections to the outside world (display, rotary encoder, etc.) are made through the I2C bus.
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Like MDRF's UDVBM-1, the digital VFO/BFO (shown here on its reverse side) for the P3ST includes a 3.3V power-supply and filter designed to keep noise from coming in or going back out the 12V power line.
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P3ST Sales Info
The regular price for the full P3ST kit (all PCB boards, components, RG173 coax, and online manual and documentation) is $109.95. As an introductory and holiday offer, the price will be $99.95 through 1/3/2024.
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A kit of just the motherboard and all module PC boards is available for $34.95.
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A set of all seven toroid coils and transformer is available pre-wound for $34.95.
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Prices for individual modules TBA.
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Sales will open December 26th through links on the P3ST product page on the MDRF website.
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Please note: This is a pay-as-you-go venture for MDRF. The purchase of kit materials and components will take place in batches of at least five kits after their sale. Shipment of kits to buyers will take place 14 days after each batch is full. Buyers will be alerted by email for any delays.
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