Build a K9AY Receive Antenna (Mains Powered)

Synopsis - What is this all about? Just what is a K9AY? Why would I need one?

A lot of today's modern home-based radio stations, whether ham or shortwave listeners, need to be able to hear the weak signals in the ever growing noise. Often, this can only be done with directional antennas and this can be expensive to implement at low frequencies. A recent design by Gary Breed, K9AY, produced a terminated loop antenna that can be electrically steered from a remote location. It offered directivity to remove or find signals and required smaller space than earlier EWE designs. This meant it was far more portable, can be easily built and can be used in smaller gardens/backyards (which is also now more common).

A copy of the original K9AY article is here. Or you can get a re-print of it inside the ARRL's book on wire antennas, 'ARRL's More Wire Antenna Classics'.

Take time to read the original article to understand the on-air performance you can expect, what components are required to build one and the level of expertise required to build and test.

For the sake of brevity, throughout this article, the radio station end we'll call the Station Switch Unit (SSU or the big box) and the antenna end the Antenna Relay Unit (ARU or the little box).

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).

Build Items

You will need a number of components to build the Project and none of them are exotic. 

Main items are as follows (with some guidance)

• Enclosures - One enclosure for the SSU. One unit (weather proof) to connect the antenna loops to and house the relays (ARU).
• Strip board - Any strip board in the junk box will do, or purchase some from Maplin in the UK.
• Terminal Posts - There are four terminal posts for the two antenna loops and one earth post which is different to be obvious that way as an earth.
• RF Connectors - As noted above, I used 'F' connectors on this unit.
• Wire - I don't have a part number for these, but get about one metre of 0.5 mm hook-up wire of various colours.
• Rotary Switch - As noted above, you need a four pole switch to switch the relays.
• Mains switch - This can be anything you have already, but do aim to get a light on it for safety.
• Transformer - A 12VA transformer is fine and second hand is just as good as buying one. You will need 12V on the secondary.
• Diodes - Basic 1N4001s are fine.  
• RF Choke - Nothing exotic.
• Capacitors - There are two electrolytic capacitors on the SSU and two on the ARU. You will also need two disc capacitors on the ARU and one in the SSU .
• Relays - You will only need two relays. These were wired in, but you can use sockets of you like. These are as per Gary's design.
• Resistor - You need one resistor in the ARU for the LF band you're interested in. A 470 ohm was used as a compromise on 160m and 80m . A high wattage (7W) was used just in case there is RF about, but a smaller one will work just as well. See Gary's design if you want to adjust this for other bands or use a variable resistor as shown in one of the pictures below (but not used here).
• Fuse Holders - The original design requires two fuses, but I put an extra one in to be on the safe side. One is used as a secondary fuse from the mains inlet and the other to the lower volts out to the relay box.
• LEDs and Holders - These are useful for indicating what's going on. I used 12V types for ease of use as I like lights (flashing or not), but you don't have to use them.
• Ferrite / Impedance Transformer - You could buy this, but I didn't find one pre-built. So you'll have to make one of your own. You need the right core and some single core wire. The core purchased in the UK from Radio Spares (www.rswww.com) come in a bag of 10 as that was the smallest number you could buy at the time.
• Miscellaneous - You will need some small nuts and bolts to hold the transformer in place. Some small 'spade' crimp connectors on the mains switch and off the back of the IEC socket if yours has them. Two PCB stand-offs to hold the power supply strip board away from the case. A knob to go on the rotary switch.

The following gives some pictures (larger images at the bottom of the article). I've not shown below the IEC connector, the F-type sockets, the capacitors, hook-up wire, strip board and the transformer. But I hope you get the idea from these what you need.

The boxes and the switch knob	Resistors
Terminal posts, strip board offset and alternative stainless steel bolts	Mains switch, relays, fuse holder, 100uH choke (alternative) 1n4001S's and ferrites.
LEDs and a rotary switch.

Maplin Parts List

I have used Maplin Electronics for just about all the bits as they have a good mail order service and shops around the UK. All the part numbers below are from Maplin unless otherwise noted (Prices as per Summer 2007).

SSU

Qty and Part #	Description	Price each	Total
1 x BX03D	Disc 0.1uF 50V	£0.11	0.11
1 x FF75S	Rotary SW4B	£1.93	1.93
2 x QL73Q	1N4001S	£0.11 ea	0.22
2 x GU73Q	Panel Fuseholder	£0.84 ea	1.68
1 x N01CF	Chassis Tx 12V/ 12VA	£6.51 ea	6.51
2 x VH42V	PC Elect 220uF 35V	£0.38 ea	0.72
1 x WH41U	RF Choke 100uH	£0.44 ea	0.44
1 x XB68Y	Chassis AC86	£5.22 ea	5.22
1 x GJ84F	20mm 250mA QB fuse  (10 pk)	£1.21 ea	1.21
1 x GJ88V	20mm 630mA QB fuse  (10 pk)	£1.21 ea	1.21
4 x UK15R	LED Clip Concave 5mm	£0.36 ea	1.44
4 x CJ63T	5mm 12V Red SB LED	£0.47 ea	1.84
1 x RD18U	SP Neon Rocker Sw	£1.73 ea	1.73
2 x FE98Q	F Type panel socket	£0.79 ea	1.58
			£25.84

ARU

Qty and Part #	Description	Price each	Total
2 x BX03D	Disc 0.1uF 50V	£0.11 ea	0.22
2 x KQ68Y	GenElect 47uF 35V	£0.16 ea	0.32
2 x N31AW	5A DPDT 12Vdc PCB	£1.98 ea	3.96
1 x L470R	7W W/W 470R	£0.37 ea	0.37
1 x YM90X	Small Waterproof Box	£4.23 ea	4.23
4 x N51AQ	Terminal Post with Large Handle	£1.49 ea	5.96
1 x JL99H	Grounding Post 4mm Socket	£1.09 ea	1.09
1 x FE98Q	F Type panel socket	£0.79 ea	0.79
2 x QL73Q	1N4001S	£0.11 ea	0.22
1 x 467-4138	Toroid Ferrite,Toroidal,43 Material,850 Initial Perm.,21x13.2x6.35mm,400nH min. AL (Radio Spares)	£0.44 ea (you buy in 10s)	0.44*
			17.60

*I've ignored the fact it's £4.40 on the basis you can buy only in tens. You also need to arrange for an account with RS and the postage on one or two items is not small. If you can find a similar specification from Farnell Online or your local supplier, please do.

Other Items

You will also need to include the following:

• Hook-up Wire - various colours, 0.5mm
• Copper Strip board
• Antenna loop wire (20m+ or at least 60 feet)
• Pole to hold it all up and some non-conductive string to hold it all in place

How to keep the cost down

The final cost of all the bits is £43.44. Not a small sum for just a receive system. So to cut the costs, here are some suggestions to get the Project bits for well under 20 pounds:

• Find a mains transformer (12v secondary) from an old power supply (£6.51)
• Find a box for the SSU from an old unit (£5.22)
• Find an out-door box for the ARU from the junk box (£4.23).
• Use M3 steel bolts instead of terminal posts (£5.96)
• Don't bother with LEDs (£5.28)
• Also consider NOT using the wire wound 470 ohm resistor (£0.37) - it is slightly inductive anyway, but not dramatically.

If you try really hard like ON4WW did here, you may even get this in for under a tenner.

Total saving £27.57

Building

Before we get the soldering iron out ...

Firstly, this project was the first prototype based on reading the original design and therefore there are some things I'd probably do differently if done again.

I also accept there are probably a lot of design rules for mains power devices out there. As I'm not with degrees in electronic engineering, I accept that someone out there may be aghast with horror either in the quality of the prototype or any potential hazards within it. As it is caveat emptor, I am applying this to myself, but always welcome comments to improve. Therefore feel free to let me know if there are good/better/safer ways of doing this.

Station Switch Unit

I won't tell you how to drill holes and cut bits out, so use your experience to work out how to do these and sweep out any remaining metal particles that you can see.

1. Work out where you want the various switches and so on on the front and back panels. Lights, rotary switch, fuse holder/s, mains input, mains switch and the RF connectors.
2. Cut and drill holes in the chosen locations. I tend to line these up so it looks neat enough. In my case, the rotary switch has a small pin to locate it in the panel and stop it rotating in use which meant an extra hole was needed.
3. Mount all the externally-facing hardware in place and make sure they are secure.
4. In this case, I put the mains transformer on the base of the box for ease of maintenance (which folds out as per the pictures below). Put it roughly in the middle of the plate so the unit is 'balanced' in your hand. Whatever you do, wire the mains transformer so that it is easy to get at for attaching and soldering the wires to it and make sure it cannot make contact with other metal parts. I'd suggest putting some sticky foam strip underneath, or on the upper side of the case if you are worried about this potentially shorting out to the case. Drill the holes (two in this case) and bolt the transformer to it so it doesn’t shake loose (which it can, as it will gently vibrate in use because of what it is).
5. Assemble the strip board as per the original Design, using the relevant components. I won't give a line by line on how to do this, as it should be easy enough to work out from the pictures below. When you have finished building make sure that there are two holes that are isolated from the rest of the board for attaching to the stand-offs. Also make sure there are no solder bridges.
6. Attach hook-up wire to the mains transformer on the 0-12v secondary and also hook-up wire to the rotary switch. I use differing colours to make debugging easier. Make the wire long enough so you can work on it if needed.
7. Do the same hooking-up of wire for the output from the unit to the antenna out socket fuse holder and then from there to the output socket itself (to the ARU).
8. Lastly, put the 0.1uF non-electrolytic capacitor to the radio input socket to. Do not simply join as you will put a lot of AC direct into your radio if done this way and you will get a radio repair bill later.
9. Now connect the mains input to the mains fuse holder on the live and then from there to the mains transformer primary. The unit should be earthed and I put the mains earth to the case.
10. The only thing left is the rotary switch. Take the four wires to the rotary switch from the strip board and hook these up as per the Design. You should have three of the four outputs with volts on of some kind and one with no volts.
11. I also had some red 12V LEDs, so I used one of the poles to apply 12V AC to one of the four LEDs from the second 0-12V AC output from the mains transformer. You can leave this off if you don't need it.
12. Do a visual inspection and tidy up the wiring with sleeves, PVC tape or cable ties as appropriate.
13. Don't power up just yet.
     

Antenna Relay Unit

As before, I'll assume you're happy to cut and drill your ARU your way. Before we get going, make sure the size of strip board will fit into your ARU and that it can be secured via off-set posts or similar in the case itself. This Project used a weather proof case with holes ready in place, so I just need to screw it into these holes.

1. Again work out where you want the external connectors and so on on the bottom panel (out of the weather). In this case these are the five various terminal posts and the F-type RF connector.
2. Cut and drill holes in the chosen locations. As before, I tend to line these up so it looks neat. It also helps to label these now, so you know what is what. Mark the direction or function inside and/or out - whatever suits you, but make it so you can see it easily.
3. Build up the strip board as per your Design schematic taken from the original design. The only tricky bit is making sure you've wired the relays the correctly. To help, I scratched a number onto each relay so I can tell which is which and also noted this on the underside of the strip board.
4. Build the nine-to-one transformer as per the original Design. This is what they call tri-filiar (three wires in plain English). I used some 0.5mm single core wire from an old telephone pair (do use single core wire that is insulated). This can be a bit of a fiddle, but if you follow the spec for this it will work. Before winding on five turns, I labelled the end of each wire A->B, C->D, E->F, to track what I was doing. Looking at the diagram, if A is at the bottom and connects to capacitor C2, B goes to the middle of the RF connector but is also connected to C. D then connects to E and last F connects at the top to one of the capacitors (C1). Do keep the windings nice and tight when winding. I believe in principle you can measure the impedance step/up (or down) with a network analyser. In this case, I simply wired this up and secured with small cable ties on the transformer itself and to the strip board to stop movement.
5. Again, make sure you've a hole somewhere that is isolated (copper strip cut so no short circuits) and that you can attached to the case. It will work without this and it can be loose inside. However, over time if the unit is shaken, dropped, etc, then a fault may develop so avoid that now.
6. Wire the strip board to the terminal posts (for the two loops). Again it's suggested using coloured hook-up wire and again make it different colours so it is easy to follow and/or debug later.
7. When you have finished, check that your wiring is as per your Design and make sure no solder bridges, etc.
8. By now, you should have a working ARU, but we need to test everything.
    

Testing

Testing is a process to make sure it is working as expected. The following is to help, but is not exhaustive. Use your brain and work through your problems in a logical fashion when the text below can't help you.

Station Switch Unit

Testing the station switch box requires a volt meter (VM) and your eyes. Do not connect the ARU just yet. We'll test the SSU first.

1. Before anything else, check you have no loose connections and that your paper schematic (with colours noted) is as you expect it to be.
2. Make sure all nuts are tight and no hardware is shaking about.
3. Before applying any mains current, check your fuses are in place and that they are not blown. Use your eyes or a VM to check continuity.
4. Have one last look.
5. Connect the IEC cable, and apply mains power by pressing your switch (you should have one). If there is a light in the switch and you've wired it correctly, it should come on. If not, stop, disconnect the mains supply to the unit and work out why (carefully).
6. Check the volts to the mains transformer and verify there is a mains current on the primary using your AC range on your VM. If not, stop and work out why (carefully).
7. Check the secondary and verify you have 12v AC (in the case of the project, there are two so I checked both). If not, stop and work out why (carefully).
8. If all is well, you may also notice an LED come on (or not if you didn't put any in your design).  If there are indicators and they do not light up, stop and work out why (carefully).
9. From the output of the 'rectifier' board, check that the volts changes for each turn of the knob. You should have four notable differing voltages. These are sent to the ARU. If you don't have these, stop and work out why (carefully).
10. Check that there are no volts at all going out the transceiver socket. There should be no current and no volts here or your radio will not last long. If you have some volts here, stop and work out why (carefully).
11. If you get to here, you've probably got a working SSU. Now go and test the ARU.

Antenna Relay Unit

1. As before, check you have no loose connections and that your unit matches your paper schematic (with colours noted) and is as you expect it to be.
2. You should now be able to test the unit by applying 12V DC from a small current-limited bench power supply. Use a current-limited bench supply set to a few millimaps so that if there is a problem, then devices wont burn out. By applying 12V DC to the relays, they should switch (click) and select one loop or another - use your VM to check which one is switched to the 470 ohm resistor (or whatever resistor you chose) to earth. Although I didn’t use them, you could introduce a pair of 12V LEDs to indicate which relay is energised (on the strip board) or externally to show that volts are in the unit from a visual inspection.
3. Now connect the SSU to the ARU with a single coax cable from the SSU antenna out to the ARU in (a short piece will do). If you hook up to the SSU radio output socket, nothing will happen.
4. Power up the SSU and hopefully the lights come on and that's all.
5. With your VM connected to the ARU earth, turn each of the four positions on the SSU and verify that each loop terminal post goes via the 470 ohm resistor to the earth post. If it does then you're finished. If it does not, go back and recheck everything again.

Congratulations - you have a working unit! Now lets have a go with it.

Using

The system was used for the first time in the July IARU contest 2007. The loops were supported by a single 8 metre (24 feet) fibre glass vertical, held in position by some string. Two loops of 1mm white multi-strand wire were used for the antenna itself. Each loop was approximately 20 metres (60 feet - this can be as long as 84 feet for 160m or under 50 feet if 40m). The two loops were also held in place by four pieces of string - one for each corner.

At the base of the vertical, an earth rod was inserted into the ground to about 1 metre (3 feet). The relay box was wired as per the original article to the two wire loops. The earth post was wired to the earth stake. Because the 50 ohm RG58 feeder coax already had male PL259 connectors, I made two 'tails' to go from PL259 to the F-type as used in this project. This left the antenna end ready to go.

At the station end, the relay box was placed on top of the transceiver (FT1000MP in this case) and then a third 'tail' from F-type to PL259 was connected to the 'receive' antenna socket on the FT1000MP. The unit was switched on as shown below.

K9AY switch box in use

To my relief, the system worked as expected and provided the directivity as per the Design. There was no mains hum or other issues. There was plenty of signals on 80m (as above) and it did not need a pre-amp.

On further use, it may be better to experiment with differing size wire loops to vary the level of signal.

Modifications

While it works well, there is always something else we can add to the project. Possible future modifications to this project include:

• Pre-amp - There is space for a pre-amp in the SSU should the loops be small and need a signal boost or if the system is more than the 40 metres away (in the above it was close to the radio). There is a 12v source and this could used to easily power the pre-amp via some DC rectification.
• Remote Band Switch - Obviously this Project was built as per the original Design. I know others have used vactrol-type variable resistors, so the antenna can be tuned remotely (variable resistance changes the frequency the ARU is favourable on). I guess if you can switch the unit to the band remotely (or a couple of switches inside) that may give a better match and slightly better performance.
• LED indicators on the ARU - next time I'd probably include these so you can tell if it is switching and that it is energised from the station end.

Where next?

Good luck if you have a go at this project. I am sure you will find the build phase just as rewarding as the use of the receive system when finished.

If you do have a go, please take great care of building a mains version and take note of the warnings above. Mains power can be fatal if care is not taken in construction and use.

Happy DX-ing!

73 de Darren, G0WCW - July 2007.

ARU and SSU plus patch cables to PL259.	Main two units	Front detail of aerial-end switch.	Another view of aerial-switch
The station-end switch unit. This has the mains power switch (illuminated when on), four LEDs to indicate direction and a four-way rotary switch.	Underside of the station-end switch. This shows the rubber feet and the two sets of screws holding the strip-board and mains transforemer to the base plate.	Initial opening of SSU unit.	Internal rear view.
	ARU opened up.
		Underside of the strip board. Note the relay positions are numbered..
	Strip board via of SSU
	The bare SSU/ARU boxes before use plus a knob for the rotary switch.	The 7W 470 ohm resistors used bare plus a 1000 ohm pot for possible alternative use.	The terminal posts (two options here), plus small stainles steel bolts as an alterntive.
Mains switch, 12V relays Fuxe holder, alternative 100uH choke (sealed), the ferrite cores anda couple of 1N4001S's.	Some other bits here - LEDs plus the 5mm bezel mount and two of the rotary 4-pole switches.

Last updated 24/7/07 - ©2007 Darren Hatcher