C Band Transverter For Phase 3D.
This transverter is not designed as a kit, but it does show the relative ease with which microwave circuits
can be designed and constructed.
The board operates from an 8 Volt supply and uses Monolithic Microwave Integrated Circuits throughout the design..
A brief guide to the transverter.
The circuit has a transmit up converter from 434MHz to 5668 MHz for P3D and also has an independent receive converter which can be used to listen for other local C band users. Alternatively, the PCB can be used on the 5.7GHz terrestrial allocation. An I.F in the 70cm band was chosen to ease the filtering requirements
The design uses 50 Ohm Microwave integrated circuits throughout. These include ERA2 and ERA4 amplifiers and Mini Circuits SKY60 mixers. An external 1745MHz local oscillator is required at 2 - 5mW. This is multiplied on the transverter PCB by an antiparallel pin diode frequency tripler. - A Hewlett Packard HSMP 3822 diode pair.
The local oscillator and C band signals are
filtered by resonant cavities. These were originally designed for
use in the G3WDG range of 10GHz kits. However, they can be easily retuned to
5668 and can just about be persuaded to work at the local oscillator frequency
of 5.2 GHz
PCB mounted in a tin-plate enclosure prior to fitting the components
Connectors for the microwave signals
In the picture above, the local oscillator input is on the right. The design uses an MGA86576 as an LNA. An external receive pre-amp can be used for a lower noise figure.
Ground plane side of the PCB showing the filters. The
small board is the +7dBm local oscillator
Two filters are used for the TX and local oscillator chains. A single filter is used in the receive path.
The local oscillator is built on a G0MRF S band to 70cm converter PCB
The completed PCB prior to optimising the noise
figure and interstage matching.
Local Oscillator input is top right. The +7dBm input is attenuated and then amplified by an ERA4. A dual diode generates harmonics, the third is filtered by the two cavities. The output is split between the two mixers with a printed wilkinson divider.
70 cms input for the transmit chain is at the top of the picture. Input is 10mW input for max output.
The receive path comes in at the lower left, passes through an ATC porcelain capacitor to the input of a MGA86576. The output goes to a cavity image filter. A small matching microstrip is printed on the board to match the LNA to the probe exciting the cavity filter. The 70cm output from the SKY60 6GHz mixer is attenuated by 3dB and then amplified 10dB in a MAR3 MMIC.
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