1.2GHz TRANSVERTER

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Front view. The status LEDs are visible. A solid READY LED (green, top) indicates control signals between radio and transverter are OK, blinking indicates an unconnected status. TX LED (red, middle) turns on when in transmit. A solid LOCK LED (yellow, bottom) indicates that the internal RF synthesizer is locked to the external reference, if it is blinking the synth’s PLL is not locked.

This 1296MHz to 144MHz transverter was designed and constructed as a relatively simple and compact apparatus for use in portable operations. It is a conglomeration of previous experience in designing such stuff :). It is designed for interoperability with the Yaesu FT-817 radio. It accepts an external 10MHz reference (eg. from a GPSDO) for improved frequency stability.

The main transverter board has the SI4133 RF synth and an AVR ATtiny13A microcontroller for the local oscillator generation. The whole stage is based on the generic SI4133 RF synthesizer board that I use. The mixer is a MINI CIRCUITS ADE-5. At the IF stage there is a 27dB attenuator (at the TX section). TX/RX IF switching is done using PIN diodes (BAR50-02V). After the mixer a printed hairpin bandpass filter (following and verifying W1GHZ’s published dimensions) filters out the image response as well as the LO. At the output TX section an ERA-2 followed by a GALI-84 provide up to 100mW output power. At the RX side a PGA-103 followed by a MAR-6 provide adequate gain and low noise figure. Switching is accomplished again with PIN diodes (HSMP-3894).

Under the main transverter board resides the sequencer built around an AVR ATtiny44 microcontroller. The firmware is written using BASCOM-AVR. Underside the sequencer there is the frontend interdigital bandpass filter constructed following the ARRL Handbook (Year 2005, chapter 12, Fig 12.41).

In the metal box there is the transmit module (RA18H1213G, the PCB is PE1RKI’s) as well as the output TX/RX relay (Axicom HF3-56). Under the heatsink there is a small board which controls the twin 4cm fans (powers them when the heatsink temperature increases over a certain temperature, sensor is a NTC thermistor).

The enclosure is made of 1mm sheet metal and is spray painted. Dimensions are 13x8x20cm

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Back view. From left to right: +12V supply connector (Anderson powerpole), control signals connector (8 pin mini-DIN), 10MHz external reference connector (SMA), IF connector (BNC), 23cm connector (N type).

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The transverter stack on the left and the PA module on the right.

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One side…

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…And the other side.

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On top of the stack there is the main transverter board, in the middle is the sequencer board and at the bottom is the frontend bandpass interdigital filter.

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The PA inside. From top to bottom: Two 4cm fans for cooling, the PA module’s PCB, the RA18H1213G PA module and the TX/RX relay at the bottom.

block

Main transverter board block diagram.

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