How to build a K9AY from parts



Design and Build Criteria

Before we start building, you need to consider a number of important points before you go forward with a design and then build a K9AY system. And there are two important safety considerations to think about. It is you that will be responsible for your own equipment/life and the lives of others if things go wrong.

  • Do you have room for one and be SAFE? They need a space about ten metres by ten meters (30 feet by 30 feet). You also need a pole in the middle to hold it all up. I use an eight metre fibre glass pole (ok, an ex-fishing rod) and that works fine. Can you fit one in your space and be safe?
  • Are you happy to work with mains power and be SAFE? The original Design from Gary Breed uses a mains power supply which in North America is 120 volts AC. In Europe mains power is roughly 230 volts AC. Either way, you can get a nasty 'nip' or things can catch fire if mains power is misused. If you are not happy or competent to use mains power in a project, then the system shown here will need slight modification. This modification is in Gary's original Design and was included where earth-loops cause a mains 'hum' on the received signal. This alternative switching method means you need both a coax run for the received signal and a second control cable (of wire pairs) to remotely switch the relays. Are you able to work with mains power in your project?
  • Do I have the skills to make the unit? You'll need to be handy with a soldering iron, some metal cutting and shaping and lastly the ability to do some fault-finding if the unit doesn't work as expected. If your not too good, get some practice first before having a go. This is even more important for the mains-powered version as there will be a lot of volts in there.


If the answer to any of the above is no, then please consider purchase of a commercial unit (e.g. direct from K9AY or Wellbrook) or borrow one from a friend. Because of the desire in the modern age to seek damages for the slightest minor problem, I can't and won't be responsible for any problems or issues caused by not taking the above into account. It's your project, YOU are responsible.

Ok, having got some health and legal warnings out of the way, we can return to the fun stuff.

Other design items to consider are:
  • Connectors - I used "F" type connectors, designed for UHF satellite TV and are easily available. They also tell the user that this is not an RF carrying system by avoiding using PL259-type connectors. Select what you have to hand but you will need three for the signal interface (one on the ARU and two on the SSU). You may notice a lot of commercial units going this way (e.g. DX Engineering).
  • Mains Interface - I chose to use IEC cables to connect the mains unit to the SSU (i.e. the mains cable you get with a desktop PC). This is because these are widely available and means that the unit does not have a lead hanging out the back. You can also get a built-in mains fuse into the holder (as used here).
  • Loop connections - Often these systems are temporary, so it's easier to use terminal posts to connect the bare antenna loop wires to the ARU. I chose these for the loops and the earth point, but you can up-rate slightly by using banana connectors into these terminal posts.
  • Wiring - To help the build process, I used 0.5mm hook-up wire in a number of colours. This helps debugging and also reminds where the volts are. If you choose to use the same wire everywhere, this will make debugging harder later. I also use enough wire so that the unit can be split into two for easy build and debugging. When wires are in pairs, use with either sleeves (nice and tidy) or as in this case, small cable ties to bunch them together. This keeps it neat and stops wires getting snagged so easily.
  • Indicators - I chose some red 12 volt LED's with a bezel mount. They are easy to fit with a drilled hole and means you can take the LED out later if required. The other item here is that I use the 12 volts AC from the transformer secondary to power the four LEDs. Technically the LEDs will flash, but as its a reasonably fast AC on the secondary, you don't really notice and it is only a few mill-amps anyway. You don't need pretty lights if you have a knob and some indication on the front panel. I also chose a mains switch with an internal light to indicate that it is on. This makes sense from a safety point of view to really tell everyone the mains is now energising the circuits.
  • Switch - I chose a cheap three way, four pole rotary switch. This has one pole for the relays and one pole for the LEDs. One pole is not used.


Your Design is important as you may want to deviate slightly from the original K9AY design based on the above. So it is suggested:

  • Draw your own version of the original Design for you to follow.
  • It's suggested that you note the coloured wires you'll use so you can follow this as you build.
  • This then makes it easier later to follow and be sure it's wired up correctly.
  • And if you're really good, stick this design inside the lid to remind you in six months time what is what (you will forget).


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