Building the RC-Dipole

Click here to open or download dimensions of 80-40-20 m RC-Dipole.

1. I used 1 mm copper clad steel wire. High pressure PVC water pipe off-cuts with end-caps as the centre insulator and as the coil former.

2. For my coils I calculated the number of turns for the coil using 60 mm coil diameter and 1 mm Cul wire. 33 turns on a 60 mm former with a length of 39 mm. Calculated inductance 59.336 µH, close enough.

3. I then wound the coil (L1) onto the former (PVC pipe) measured it (59.29 µH), cut the former to length and wrapped the turns with PTFE tape (plumbers tape) to limit water ingress. NOTE: Try to wind the turns as close to each other as possible.

4. Then created wire-loops on the end-caps and glued the end-caps in place.

5. The centre insulator is made the same way as the coils with the exception that the RG-58 is feed into the pipe, which then will be soldered to the wire-loops inside the pipe. If you would like to use a BALUN (1:1), there is enough room for a home-build balun to fit inside the 60 mm pipe. I opted not to use a BALUN at this stage.

6. Now the coil-tails will be soldered to the wire-loops and I checked for continuity between the loops.

7. Next job is to measure the two centre pieces (W1), the two pig-tails and, as I had only enough wire for one additional element , the 40 m element (W3) NOTE: I added additional wire length for the mounting and tuning of the elements.

8. Attach the two centre wires to the centre insulator, one to each wire-loop. (wrap a few turns around and solder into place)

9. Attach the coils the same way as the centre insulator, but make sure you measure W1 from the center insulator wire-loop to coil wire-loop. (remember, it is not that critical, we are at HF not VHF or UHF)

10. Now attach the pig-tails (W2) to the opposite side of the coil to the second wire-loop. I started with a 3 m long pig-tail.

11. Before attaching the next element, I STRONGLY RECOMMEND TO TUNE THE BASE ANTENNA (80 m) FIRST. I strung the antenna into the final position, measured VSWR (antenna analyser) and adjusted the pig-tails for best VSWR. (The modelled values were very close to the final length of the pig-tails 2 cm out)

12. I then cut the black poly-pipe (irrigation raiser) to 40 mm and attached approx. 20 to each side of the 80 m element (the W1 wire) and attached the spreaders to the main element looping the 100 mm x 1.5 mm cable-ties through the raiser pipe.

13. Mark the center of the 40m element and feed through the spreaders.

14. IMPORTANT! MAKE SURE THE WIRES DON'T TOUCH!!

15. Repeat step 12 to 13 for the 20 m element, add the spreaders to the W1 wire first and then add the 20 m element. It might be a good idea to add spreaders between the 40 m and 20 m element. Your mileage will vary.

The VSWR on 40 m was spot on and the VSWR on 80 m improved as the model predicted. The antenna was up in-time for the VK Remembrance Day Contest and I was able to work 80 m for the first time with more then a few watts into my 40 m horizontal loop. (I wish I had room for an 80 m version but …)

Well, I must say I am pleasantly surprised by the performance. I worked a few ZL's and VK6's on 80 m. A few day's before I heard a VK6 with 55 but was unable to work him with the h-loop, no real surprise there. Basically, everything I've been able to hear, I was able to work.

I'm also surprised at the quietness of the antenna on 40 m. Initial test towards the west (side on) against the 40 m h-loop shows a 2S points difference. RX test on YB stations (North) show better performance on the dipole then the h-loop, which seem to confirm the pattern. So what about 20 m? Well, as soon as the weather permits I'll add the 20 m element to the antenna.

I have a bit of space from the back of the property to the TV aerial. Time to model a 30-17-12 m RC-Dipole and build an antenna for the new OLD WARC bands.

Parts list:

• • • approximately 70 m of wire. I used 1mm copper clad steel-wire. Yes it can be 2 or even 2.5 mm the dimension won't change (very, very small change, hardly noticeable),

    • 2x coil formers, I used 60 mm high pressure PVC water-pipe from the local Hardware Store ,

    • 1x centre insulator, again 60 mm PVC water-pipe,

    • 6x 60 mm PVC water-pipe end-caps,

    • 6x 405 mm irrigation raiser pipe (black poly-pipe, UV stabilised),

    • black (UV stabilised) 100 mm x 1.5 mm cable-ties,

    • 15m of 1mm CuL wire (lacquer insulated copper wire),

    • 1x Roll of PTFE tape (plumbers tape)

You can change the coil former to a smaller diameter, but I would suggest not to go below 40 mm.