|So... I was getting dissapointed with the Slinky Antenna I designed and built as it did not live up to my hopes. Having a small garden definately has its disadvantages... Anyway, next on the cards was a Delta Loop Antenna. Once again, due to lack of space, this is a compromise as it is only a single element bit it is still directional and takes up much less a footprint as a beam or long wire.....|
|So... where to begin? My starting point was to make a bracket which was quite sturdy and cheap. No need to throw lots of money at this project, it can be put together quite cheaply. The bracket itself cost me nothing as it was a thrown out length of dexian racking. I drew a straight vertical line on a big piece of paper then two other lines from this at 45 degrees. Where the lines met at the vertical line was 90 degrees in all which is the angle you need at the bottom of the V. I used this as a template for marking the dexian. I cut 2 lengths of Dexian just over a foot long for the sides. Then I cut 2 more pieces for the cross members which would hold the two arms of the antenna in the right position and also be used to clamp the whole affair to a pole. These were then bolted together with M8 Fasteners. I slit the cross members at both ends and knocked the ends up at 45 degrees so there was extra fixings and strength when bolted together at the sides..|
|It is really at this point you need to clean off any grotty bits and paint preferably with some hammerite. The bracket clamps are next. These I bought from Halfords, 3 at 99p each. Two are for mounting the bracket itself and the other for mounting the perspex plate (You will see this shortly) These are meant for exhaust pipes but are absolutely ideal for this. My pole which is a standard antenna pole is 1 1/2" so the brackets need to be 1 5/8". So now the project has cost me £2.97 (The nuts and bolts and paint I already had). Then you fit the bracket to the pole as below.|
|Next up is the poles themselves. These are made up from fiberglass fishing rods. Do not use carbon fibre. I bought mine off eBay from Dowlings Outdoor Sports. These are 5m rods and are strong and extremely light. Their eBay advert title is "LINEAEFFE FISHING FIBREGLASS WHIP + RIG 5M 5 METRE NEW" Item number 170551802703, Which are a bargain at £4.65 each + £1.95 each postage. I thoroughly recommend this supplier, they are very good. Phone 01753 653 733 or email firstname.lastname@example.org.|
|Right then, 2 x £4.65 = £9.30 plus 2 x £1.95 = £13.20. It came at £12.50 to me as there was a little postal discount for the two items so £12.50 and £2.97 = £15.47 for the project so far. (2010 prices)
What to do with these... They are telescopic and the top section is useless so it can be discarded. The second section needs approximately 9" cutting off it. Then, from the cut piece measure down the fully extended pole to approximately 3.6m (for 11m) then cut the bottom section off at this point, do exactly the same to the other fishing pole.
|I had a lucky break on the cable. On one of my trips to LIDL I happened upon this reel of speaker wire. 20m on a reel for £7. This was stranded 1.5mm so with both wires stripped and twisted together it was 3mm thick. I nearly used clothes line with the steel strengthener for this until I spotted the speaker wire. The grommets you see I already had and are for running the wire through and fitting in the end of the fishing rod to prevent chaffing of the wire. So now the project has cost me £22.47.|
|11m - 27.555 MHz|
|The calculation I was given with the wire was each of the 3 sides needs to be 3.665 mm long for 11m. I measured 3,665 mm then marked the cable with a permenent marker, then again from this point measured 3,665 mm and marked it again. Then I measured the final 3.665 mm from this last point and then cut the cable. I fixed thick tie-wraps on the two marked points and then using soapy water I slid the grommets along to the tie-wraps. See the left picture above.|
|Then, slide the speaker wire through the top of one of the fishing poles all the way through until you reach the grommet which will then fit snug in the top of the fishing pole (see above left) Do the same with the other end of the speaker wire through the other fishing pole resulting in another snug fit. There should be approximately 60mm of cable exposed at the end of the fishing poles, strip these back about 10mm then twist them together. I then used a yellow crimp connector on both of these so that I could attach them to the perspex plate seen above left. This perspex plate is fixed on the supporting pole with the third of the exhaust clamp brackets. Also through this perspex plate is two M5 bolts so a 9ft piece of 75 Ohm co-ax can be fitted to the antenna wire easily, this is for matching purposes. You could use choc blocks for this but as I had the crimps already I decided to go that way. It also takes all the strain off the co-ax.. At the other end of this 9ft piece of co-ax fit a PL259. Then you can run this to your station using normal 50 Ohm co-ax|
|As you can see to the left I have used tie-wraps to anchor the poles to the bracket. This is only temporary as I have ordered some Jubilee clips off eBay to complete the job properly. The jubilee clips cost £1.40 for 4 with 79p postage but are the good quality ones not cheap rubbish. . These are 32 mm to 50 mm and are stainless Steel. Ebay item number 220685889791 from "onlinemotorfactors", which should be plenty big enough. You only need 4.
Also, between the poles and bracket I have strategically placed rubber feet to lift the fishing pole away from the fixing bolts of the bracket in case they caused damage over time to the fishing poles
|The only other thing to mention is at the point of joining the 50 Ohm co-ax to the 75 Ohm co-ax I made a choke balun consisting of 7 windings of the 50 Ohm coax.
On test it was noticed that the constant 3 to 5 of hash I was recieving on the vertical antenna was no longer an issue with the Delta Loop as It sat back to 0 on the meter. This in itself is very important as some stations lower than a 3 you would not even notice so on that point alone the Delta Loop is a winner.
Over the coming months I will be doing checks on tx/rx on other bands as I do have a very good antenna tuner, also I may make one in the future for 20m. This one will mainly be used on 10m.
The SWR was not at it's best with the copper wire although it was ok so
I decided to experiment with a piece of solid Aluminium wire obtained
from "floristrywarehouse" off eBay. The item number at the time of this
update is 180534028994 or just do a search for "Aluminium wire floristry
craft jewellery silver" priced at £4.39 which includes postage. Very light
considering it is 2mm thick, very strong and the size is ideal too with just
a couple of feet left over. When you think that most homebase CB
antennas are constructed with aluminium there is no problem with this not
being "copper". The aluminium wire is measured exactly as with the copper
speaker wire detailed above. I also used the same "yellow" crimp lugs to secure the ends to the perspex mounting plate. The price of the project is now down to £19.86
To the right is a more detailed picture of the perspex plate. You can easily
see the way the 75 Ohm co-ax has been anchored by the M5 fasteners
and the tie-wraps. The antenna wires have yet to be fitted. I could have
cut this perspex plate down so it has less wind resistance, the next one I
make will be smaller. You can see on the edge of the pole bracket some
rubber feet. I used 6 on each side to cushion the fiberglass poles and to
lift them away from the bracket fixing bolts.
Next were the Jubilee clips. These were again purchased off eBay from
"onlinemotorfactors" item number 220685889791 or do a search for
"Stainless steel hose clamps 32-50mm (clamp, Clips) x 4" which is
handy because 4 is what you need. These are a bargain at only £1.40
with 79p postage and packing. The same item in Halfords cost approx. £1.99 each.
So now the total outlay I had to spend to construct this antenna comes in at approx £22.05
Once the whole assembly is finished I sprayed the connectors on the perspex plate several times with car laqueur spray to seal all the exposed parts. This I already had in my shed so cost me no extra.
NB. you can buy a very similar delta loop Here for £127 to £161 from Vortex, or make your own as above