The Lazy-D Antenna

The horizontal loop, or sky-loop has been described in [1] and [2] as a square, and at [3] as a square and octagon. I have build and used a triangular sky-loop for the last six (6) years and thought I share my experience about this antenna with you. My initial installation was at a height of five (5) meters (m) above the ground with a long run of RG-58 (16 m) and RG-213 (12 m). However the current installation is nine (9) meters above the ground at the far end corners and five (5) meters at the feed point.

I'd like to call the antenna a Lazy-Delta-Loop Antenna, or short Lazy-D. Lazy as in laying down, like in the Lazy-H antenna.

My goal was to build a square horizontal loop for 80 m (2λ on 40 m with approx. 6 dBi @ 45°), but I quickly found out that it was not possible to bring that much wire up in the air at my QTH. However,I still wanted to try a loop. So, after a bit of brainstorming I decided to make it a loop for 40 m. As I had only two reasonable high (5.5 m Al-pipes) poles and our TV aerial up on the roof as support for the antenna, I decided to build the Loop as a lying Delta, hence the term Lazy-Delta-Loop. To be more precise, I decided to make it in to an Equilateral Triangle. i.e. same length of wire at every side and same angle in each corner. I used the following formula to calculate the needed wire for the project.

I use insulated wire for the antenna element and according to the literature I should multiply the result with the velocity factor (VF) of insulated copper wire, which is about 0.95. This then would change the formula to:

The calculated length from Formula 2 is just over 40 m. However, as soon as the antenna was in the air and I started my measurements, it became very clear that the resonance frequency had shifted to over 7.4 MHz, an indication that the antenna was to short (!@#$%^, I guess I did not take into account that the antenna is rather CLOSE to ground).

This wasn't good enough and so I reached for my calculator. I scraped Formula 2 and used Formula 1, yep, not paying attention to the VF. Using Formula 1, I calculated the length of the wire to be just over 42 m. This time however, I decided to add a bit more wire rather then being to short. I extended the wire to an overall length of 42.7 m which, as I found out shortly, worked out rather well. The measured resonance (not best VSWR) was just a tad over 7.1 MHz.

Initially my feed-line consisted of 16 m of RG-58 and 12 m of RG-213 coax-cable, which terminated into an unbalanced tuner. This configuration was able to tune the antenna easily on 40 and 15 m and with a bit more patience on 160 m. However, no luck on 80, 20 and 10 m.

Well, tune the antenna is not the correct term, it should really read tune the antenna system. Tuning the antenna system so the radio is able to transfer full power into the antenna system. As we all (should) know the tuner at the end of the feedline does not change the antenna, all the tuner is doing is to make sure that the radio sees a Z (impedance) of approx. 50Ω and as such is able to deliver maximum power into the feedline. What ever power (Tuner and feedline losses play a role here) reaches the antenna will then be radiated, which might not be much.

Unfortunately I've lost my measurements (can't trust computer storage devices) so here is some modelled data of the old installation of the LAZY-D at my QTH. It is not quite the same as the actual antenna properties, as there is a big eucalyptus bush/tree in the centre of the loop, which very likely changed the characteristics of the actual antenna a tad. From the model it is clear that it should have been easy to tune the antenna on 40, 20, 15 and 10 m but, as can be seen the SWR dips at 20 and 10 m are rather high. I suspect that the feedline length played its part in being unable to tune the antenna system for a reasonable match.

Pic 2 shows us that there are four resonance dips, at 40, 20, 15 and 10 m. And at Pic 3 we have an overview of the impedance's that we can expect.

According to W4RNL [3] (SK) the impedance at the base frequency for a square loop should be 120 -j100 Ω. However, the feedpoint impedance will vary with length, layout and height of the antenna. Also keep in mind that these values are for the antenna and are not necessarily the values the tuner is presented with. The impedance the tuner sees will be a function of the transmission line length, the VF, the impedance of the line and the impedance of the antenna. According to the model, my Lazy-D has an impedance of approx. 100 +j10 Ω at resonance.

Pic 4 shows us the calculated gain distribution across our HF spectrum.

The next picture, Figure 5, shows us the 40m horizontal gain pattern, for my antenna system.

The antenna system in this configuration worked very well on 40 m and to my surprise also on 160 m. I don't think the efficiency on 160 m was anything to rave about, but I made a contact on 160 m into ZL during a contest using 50 W (he must have had very good ear's).

However, the antenna was to close to the roof line for my liking and feedline and VSWR losses also played a roll in me not being convinced that my antenna system was at its peek performance. And so, after a short while I decided to change the feedline and relocate the antenna more to the back of the property, away from the roof line. I have a drum of RG-62A lying around and so I decided to make a new feedline out of the RG-62. A shielded parallel line with approx 200Ω impedance. The length of the new feedline is 23.4 m terminating in a 4:1 Balun at the radio shack end. In theory that should give me a good 50Ω VSWR on 40, 20, 15 and 10 m. I've also found some AL-pipe to extend the current skyhooks at the far end. The antenna is now 9 m above the ground at the far end but still about 5 m above ground at the feedpoint. I need to work on that. Also, the feed point is now over the pergola rather then over the roof-line. So lets have a look at model for the new antenna system installation.

Well, as expected the VSWR into a 200Ω load is less then 2:1 at 40,20,15 and 10 m and with a 4:1 Balun at the end of the feed line, the radio should see a nice 50Ω VSWR.

As we can see in Pic 7, the impedance at 7 MHz is 93.8 -j 28.2 Ω, which is very close to what I measured with my antenna analyser (Autek RF-1). The next picture, Pic 8, shows the 40 m horizontal gain pattern. Comparing Pic 5 with Pic 8 we can see that the antenna system has improved by more then 1.5 dB. The total gain is now nearly 5 dB.

So to wrap it up, performance has improved markedly and I have managed to work some DX on 40 m with it, quite a few contacts into EU, ASIA and the Americas. It is quite quiet compared to the verticals that I have trialled in the past. It is a very good antenna for short to medium contacts up to 10000 km. Above 10000 km the verticals are about one (loaded vertical) to two S-points (40 m ¼λ with 16 radial) stronger, but the Signal to Noise ratio on receive is approx. two to four time better in favour of the loop. If you are living in suburbia a very good 40 m DX compromise is to use a Lazy-D on receive and an elevated vertical with a few radials on transmit.

On 20, 15 and 10 m the antenna works, but I'm unable to judge its performance. I have however, worked EU stations on 20 m PSK using 20 W and on 10 m 5 W WSPR. Of late, with the good conditions on 10 m I've been able to work stations in EU, Asia and the Americas.

Click on the below photo to see more on the LAZY-D.