 Our new 24GHz equipment is ready
for use since September '02. Its construction bases on modules by DB6NT and
parts from PROCOM. The layout is made by DL2ALF after a meeting with DB6NT
during the Microwave Conference in Dorsten '02. The assembling and the mechanical work is all done by
DL6AUI. In April 2004 we mounted a 1.2W - PA by DB6NT right after the HEMT - preamp to get significant more power. We kept the simple design to avoid a complete mechanical reconstruction. Because of the resulting > 40dB gain we need a transfer switch with extraordinary isolation (60dB according to the data sheet). It was risky but it works, no oscillations, normal noise figure. It is hard to accept the losses of ~ 3dB of connectors and transfer switch, we will see. The rest of the circuit including the sequencer is kept. See the technical data below : Technical Data Transverter system based on
144MHz IF and sub harmonic mixer followed by a waveguide filter and
HEMT-amplifier in coax. The meters were mounted at the end of the waveguide and
measured @ DB6NT April 2004.
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| See the bottom view of the
transverter on the small picture below. From left to right : waveguide, transfer relay, HEMT-amplifier, sequencer, 12GHz LO, OCXO and output meter. |
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See the top view of the transverter on the small picture above. From left to
right : 144MHz input, 12/24V-transverter, sub harmonic mixer, waveguide
filter, 12GHz LO, OCXO (wrapped in plastic foil), transfer relay, meter
amplifier and meter. The spare place is now filled with the 1.2W - PA. |
| Construction details : 1. waveguide/coax The waveguide/coax transitions are directly soldered to the copper waveguides. Less connectors means lower losses. 2. Transfer relay The transfer relay is rotated 45°. So the HEMT-amplifier can be mounted flat on the chassis. Remarkably short are the connections from and to the transfer relay. This is the result of a optimization process (via ATV) by DL6AUI and DL2ALF. The long semi rigid cable is a placeholder for an additional amplifier. 3. 12/24V transverter The power consumption of the transfer relay is 24V/280mA. We use an oversized voltage doubler circuit with TDA 2003. This gives a stable output of 24V/500mA (10W). The TDA 2003 is mounted on the chassis. 4. Sequencer The HEMT-amplifier is used for both Rx and Tx and is reversed with the help of the transfer relay. If you leave the power supply on during the transitions oscillations of the amplifier may occur. To avoid this, a sequencer with the shown time diagram is used.
All timings are adjustable with NE 555 timers. The outputs are switched with power MOSFETs mounted on the chassis. 5. OCXO To get a stability of the 24GHz signal within +/- 1kHz a well proven OCXO circuit design by DF9LN is used. In this case the crystal and the oscillator PCB are within a 60° thermostat. A simple plastic foil with small air bubbles (used for packaging) reduces the thermal and mechanical coupling with the chassis. |
