(Photograph courtesy of Martin Farmer, G7MRF)
This handy gadget is so simple and yet so useful! You wonder why you hadn't made it before! It consists of a microwave mixer stripline diode package soldered across the probe (spiggot) of an sma connector or even a short length of semi-rigid coax. In addition, a short wire loop is soldered in parallel with the diode to act as a DC return and choke. Both loop and diode are soldered, at their other ends, to the flange of the sma socket or to the outer of the semi rigid coax. Since the diode package used is a double array only one half of it needs to be used.
The diodes are cheaply available and are the same as used in many a Satellite TV LNB, such as those used in the UK Amstrad systems.
The photograph above shows the diode and loop mounted on an sma female socket which in turn is connected by a male-to-male sma coupler to a "brick" PLL oscillator (eg Frequency West or Continental Microwave type). The "brick" frequency should be chosen to produce harmonics on the microwave bands of your choice.
G3PHO, your webmaster, uses an Adret 5105 VHF synthesiser, set to either
96MHz or 108MHz, to drive a G4DDK001
1GHz module. The resultant 8mW or so then drives the diode multplier described above. Excellent stable and strong harmonics are easily found on all microwave bands to 24GHz. G8KMH measured the 47GHz harmonic of his marker on a spectrum analyser and reckons it could be heard over a km or so! (Given a suitable dish of course!).
The higher in frequency the drive source the better the chances of obtaining a useful harmonic on the millimetre bands such as 47GHz. An accurate source at 2350MHz producing a few milliwatts will do the trick.
G3PHO also uses a G4DDK004 oscillator module at 2419.2MHz to produce a handy portable marker for his 24GHz narrowband equipment. While this is no where near as stable as his Adret-driven marker, it does provide a valuable check that the transverter is actually working, at least on receive! A Murata crystal heater markedly improved the stability of the G4DDK004 module.
In practice, any microwave diode will work, though the stripline package shown above is very small and efficient.
There is now no excuse for not knowing your frequency on the microwave bands!
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