While lying in bed recently, my mind pondered on the QDX and it suddenly struck me that it has no manual controls at all: it is totally controlled by software. This would make it ideal for remote location, for example, in a shed at the bottom of the garden, making antenna arrangements easier and getting somewhat away from the noisy domestic location.
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Next morning, I looked up how far you can run a USB cable: answer, not far enough for my needs, but then I came across the "USB Extender over Cat5 cable".? For somewhere around ?10 or so, you can buy 2 units which you interconnect with cat5 cable up to a distance of 50m - just what the doctor ordered!
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Next, what sort of CAT5 cable to use for installation outside and probably directly buried. It turns out there is suitable outdoor grade cable available with tough double sheath and not too expensive - about ?50 for 100m. Burying the cable in the lawn is desirable for two reasons.? Firstly, it is relatively easy by using a spade to make a slit (about 150mm deep) into which you can push the cable down using a small piece of wood. The grass is then restored by pressing down with your foot. The second reason is that burying the cable gives some screening and also helps common mode rejection due to the capacitance of the cable cores to ground.
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Further reduction of common mode noise from the PC can be achieved by winding the CAT5 cable around a couple of ferrite toroids near the PC end.
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Powering the QDX is most easily done using a 12V lead acid battery which is charged up in the shack and taken down the garden for each operating session.? A suitable sized battery would allow several typical operating sessions between charges. (The QDX would need to be built for 12V operation using a 3:2 ratio output transformer rather than 2:2.)
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What about changing bands?? At first, I thought I would have to use a separate multicore cable to control some antenna switching relays. Then I realized that the QDX has band select signals to control the preselector.? BAND0 and BAND1 are output from the microcontroller to give a two bit binary output, where "00" represents the 80m and "11" represents 20m band.
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It would be relatively easy to take the BAND0 and BAND1 signals from the microcontroller (available at IC3, pins 14 and 2 respectively) and feed them to the gates of a couple of BS170 MOSFETs as relay drivers.? Two relays, one SPCO and the other DPCO can be wired to select one of 4 antennas under these control signals from the QDX. It would probably be best to put a simple RC low pass filter on the MOSFET gates to stop RF from the transmitter affecting the relay operation - that could be disastrous if it caused an incorrect band selection!
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The relays could be configured to select different ATU settings if you use a single antenna. Of course, if you have a multiband antenna you don't need any of this antenna selection arrangement at all.
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So remote operation could be fairly easy to achieve.
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However, for me it will have to remain a dream as I was 30 minutes too late to place a QDX order!
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Peter Lee
G3SPL
