Multi-band Vertical: “The 43-footer”
We moved to a new QTH in 2010 and because of lack of space in our pocket-handkerchief section, it was no longer possible to have the 67-foot/20.6m antenna which worked so well on the low bands. The hunt was on for a good compromise antenna capable of providing a decent signal on 30, 40 and 80 meter bands and could at least get a signal out on 160mb (see “Topband” below). They will give you 20, 17, 15, 12 and 10m as well so cover all the major HF bands.
The only spot available for a vertical was in the thin end of a small wedge-shaped back section (the SteppIR beam occupies the thick end). This restricted guying options and testing the new neighbours reactions to guys on their properties was not warranted. Initially, several aluminium antennas of 10 -12m with various means of loading were tried but they twice bent over in strong winds. Google was called upon for assistance and several articles on short multiband verticals featured the magical “43-footer”(13.1m) antenna. They are commercially available from DX Engineering and Zero Five antennas.
Installing a 13m aluminium antenna with the aforementioned issues was never going to happen. Fortunately, there was another option. Fibreglass “squid poles” or windsock poles are being used more and more often amongst the DX fraternity for antennas. The fibreglass poles are lightweight yet very strong though I would recommend they be guyed, mine now (thanks to considerate neighbours) has 3 guys at 10m high. Also because of their weight, they are very manageable and its a one-person job to stand them up.
Nine meter fibreglass poles are sold on TradeMe for around NZ$220 and can be extended with suitable PVC electrical or plumbing pipe. Another option is to import “squid poles” from Australia where they are a lot cheaper however, freight makes clubbing together with a few mates and buying in bulk a sensible option. Then there are the tried and true Spiderbeam poles from Germany which are very strong and used on many DXpeditions these days. My pole is a 12m Spiderbeam with a 1mm PVC extension. See the appendix for supplier information. More recently, with the growth in interest in Summit On The Air (SOTA) DX, SOTA Beams in the UK have a very well priced 10m telescopic, again it would be worth clubbing together to bulk buy them. They pack small enough to fit in a standard suitcase and have been used very effectively on YJ0X and VK9NZ DXpeditions.
If you can’t find a 13m option, you could wind 13m of wire around a 9-10m pole. On the other hand, if you have aluminium tubing to do the job and room for guying that will also make a good antenna.
The pole is saddled against a 3000 x 150 x 100mm tanalised post concreted into the ground, 500mm deep.
Because of section size limitations, burying 30+ ground radials wasn’t possible, so the wooden fence either side of the vertical is used to support two elevated tuned radials for each band. The radials are tuned exactly as you would a dipole, for lowest SWR at your freq of choice. You’ll note electric fence insulators carrying the wires. High voltages could occur at the tips of the radials so sensible precautions should be taken. These insulators sell in a bag of 20 for $12 at farm supplier stores.
Buried radials would be a better option provided you have the room, the experts recommending 36 minimum spread around a 360 degree circle. At the previous QTH, they ran in as many directions and angles as possible. Around gardens, along path edges and down the middle of the lawn. There were over 30 buried radials, most being 20m long and another 6 or so of 40m.
The easiest option is a 4:1 unun used in conjunction with your shack’s tuner. They’re easy to construct and not expensive. See Phil Salas’ article.
Unun circuit diagram (thanks to Enrico Peroni IV3SBE for the original article)
1 x FT240-61 toroid core (see Appendix)
2 x binding posts or better still, 2 x M6 x 25mm stainless steel bolts, 4 x nuts & 8 x washers
1 x SO239 socket
1 x enclosure
4 x small cable ties
3 x cable tie mounts
1 x short piece RG58 coax
4 x M3 x 12mm bolts, spring washers & nuts
1 x small solder/crimp lug
2 x 1.5m lengths of 1.5mm2 (use different coloured wires to make identifying ends easier).
6mm heatshrink to slip over RG58 end
Glass tape (optional)
Initial matching was achieved with unun above, wound on an Amidon FT240-61 toroid with 12 turns.
Note that the toroid is over-wound with glass tape to improve current-handling capability. Probably over-kill for 500W max and most construction articles on ununs don’t use it.
Underneath the unun, there are 3 self adhesive cable tie mounts which secure the core in place with cable ties.
The two wires are taped together to hold them neatly in place though simply twisting them would also work well.
Using the auto-tuner on an Elecraft K3 provided easy match 80 – 10m. The unun worked very well on 40 and 30m with no problem working into the Americas, Asia & Europe. On 80m it was possible to work longpath into Europe with 100W so the antenna was certainly no lemon… with one exception – Topband.
With the above unun, the antenna tuned poorly on 160mb with the K3’s tuner only getting an 8:1 SWR at best. Overseas articles suggested 50m of coax was required to get it to tune properly on 1.8Mhz which could be difficult to implement in some situations and an unnecessary waste of coax. Again Phil Salas’ website offered alternative matching units using a switchable base-loading design.
An SGC SG-230 automatic coupler at the base of the pole has also worked very well. The SG-230 is an excellent coupler and, according to Phil one of the few tuners capable of matching the 43-footer on 160mb, even with a short coax feed. K4M Midway was worked easily with this config.
Another solution to the 160m issue is to run a second dipole from 10m high loose back down the pole. For 80-10m, it is connected in parallel to the main dipole running up the pole, for 160m it is elevated inverted-L style and extended by approximately 25m. This design has been used to work VP6EU on Pitcairn Is.
THE 31-FOOTER OPTION
If your interest lies more with 40-10m, or you simply can’t get a 13m pole up, then you can use the same design on a 9m pole.
South Island Component Centre, 24 Essex Street Phillipstown 8011 (03) 379 8833. P/No. FEFT240-61 NZ$30.63 + shipping.
Amidon Corp, http://www.amidon.corp.com P/No. FT-240-61 US$9 + shipping
Spiderbeam, http://www.spiderbeam.com, 12m pole Euro $66.39 & shipping
Pestgard, http://www.pestgard.co.nz (kite poles) 9.2m pole $218 + shipping (these are the ones sold on TradeMe).
Haverford Australia, http://www.haverford.com.au 10m pole A$53.90 + shipping.
SOTA Beams – http://www.sotabeams.co.uk/telescopic-antenna-masts-sotapoles/ 10m telescopic poles