47Ghz Equipment
Mk 2 Transverter and FM source
This photo shows the head unit of the 47Ghz DB6NT transverter with, from lower left to right the 11.7 to 23.5GHz LO doubler and the x2 diode multiplier and mixer. The 3-stage LO doubler uses NE32584 GaAs fets in an single amplifier configuration followed by a pcb filter, a X2 stage and a final amplifier to produce ~ 50-60mW at 23.5Ghz. The upper pcb is the IF and switching. It was recognised in the first attempt that it was quite tricky to optimise the 23GHz multiplier strip due to the integrated approach. Thus this second version gets round this by having a removable 23Ghz strip which can be optimised into a power meter in its own right. Using this method 60mW has been seen at 23Ghz enhancing the mixing properties of the following mixer diode. A small screw is also visible which allows matching into the diode for best performance. High stability and good phase noise are achieved by using QT crystals in the LO from by Eisch-Kafka in Germany.
The LO comprises a multiplier chain which provides a signal at 11Ghz mounted in a back to back pair of die-cast boxes. One side contains the crystal oscillator and RF multipliers, the other a PLL using the WA6CGR system, which can be locked to an external GPS disciplined 10Mhz source. The PLL is shown below. Since the output power of the transverter is in the order of uWatts a GaAs FET multiplier producing ~4mW is available on transmit. The crystal driver multiplier chain can be either keyed or audio in the form of FM applied.
This shot shows the transverter mounted on the waveguide switch and cassegrain plastic 30cms antenna with the 4mW FM source on the Tx port
The 4mW GaAs FET multiplier, an example is shown below, comprises GaAs fet multiplier stages using the NE32584 devices, driven by an 11.772Ghz source capable of being FM modulated or keyed for CW.
And if you thought this is advanced for its time ...look at this link.
www.tuc.nrao.edu/~demerson/bose/bose.html
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MVDS unit conversion
Some time ago a Philips ex Microwave Video Distribution System (MVDS) unit was obtained with a view to modifying it from 42Ghz to 47Ghz. These are interesting units comprising a full multiple conversion receive unit down to an IF in the 1GHz region with a free running DSO local oscillator and a dielectric lens antenna. Receive performance should be good as a 42GHz MMIC precedes the single diode mixer. However the spec. sheet for the MMIC seems to indicate that the MMIC response above 42GHz may roll-off rather rapidly. So some modifications were made to the unit to check it out for use on 47GHz.
For 47GHz replacing the DSO with a fixed xtal multiplier chain at 9GHz was tried and modifying the following multiplier stages and filters. However the sensitivity of the unit was disappointing with performance no better than a DB6NT bare 47GHz mixer.
Waveguide coupling into the unit just following the MMIC was also tried ahead of a DB6NT mixer but although the noise level due to the MMIC increased there was not a corresponding increase in sensitivity. MMIC gain at 47Ghz was estimated to be ~6dB.
The photo above shows the unit with an injection of the LO at 23.47Ghz to produce an IF at 145Mhz. In this state it was on a par performance-wise with a bare DB6NT mixer and 30cms dish although it should have be considerably better.
In a further effort to make it work well on 47GHz the two pcbs containing the MMIC's were cut up and paired as shown below to try and produce a gain block, but despite the combination seeming to have gain and being quite ready to become unstable, its seems the gain is not at 47Ghz!
The verdict seems to be that these MMIC's do not operate up to 47GHz although quite happy at 43GHz. The data sheet for the device does not indicate performance at 47GHz and it must be concluded that this is the reason......unless someone knows different...................?
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47Ghz south coast beacon
Visit the web site of G8ACE http://www.microwaves.dsl.pipex.com/beacon/beacon.htm for the latest news on the 47GHz beacon