15m 6el Yagi
Monster Yagi on a 40ft boom that really works
1000+ already viewed!
Article Summary
The project of the ‘3 el 5 band quad’ was not a tremendous success as I wanted it to be. I wasn’t too happy about the back lobes on certain bands and also the forward gain compared to the G5RV.
Article Highlights
- Modelling the Yagi with YO Software
- Dimensions
- Tuning
- Performance
- Audio Clips from USA
Kamal Edirisinghe
4S7AB / KA5MAL
Apr 2003
Having More than 35 years of experience in the Field of Amateur Radio, I have published many articles in prestigious international publications like, QST, CQ-DL, NCJ, Six-News etc.. Here in this web site, these write-ups are intended to give you knowledge about my designs and projects related to the hobby. The articles about foreign HAM activities are intended to share my experience.
- Full Solar Powered Radio Station
- SO2R and Multi-Multi Compatible
- Operate on All Bands/Modes/SATS
- DXCC #61,271
- IOTA AS-003, CQ-22, ITU-41
This brought me to the idea of dismantling the multiband quad and puting up monobanders instead (Aug.2002). When you want to design a yagi, the YO software is always a handy solution. I was using it for the last 12 years and had vy good results. After playing around with a dummy design (startup design), I was able to come up with the below design having very good f/b and forward gain. The selection of the 40ft boom is another first time experiment, which turned out to be a great success.
I used 3/4″ and 5/8″ in a tapered arrangement for the elements. They are light weight on the long boom but not strong though. Hopefully they will last for many years. The dimensions are as below
| Spacing from the reflector | 0.750″ length in inches | 0.625″ length in inches |
| 0.000 (Ref) | 72.000 | 70.514 |
| 53.238(Driven) | 72.000 | 58.500 |
| 111.068(D1) | 72.000 | 57.837 |
| 193.082(D2) | 72.000 | 56.208 |
| 324.078(D3) | 72.000 | 56.932 |
| 474.666(D4) | 72.000 | 51.700 |
Tuning
Tuning was done using the good old poor man’s method of bringing the rig to the rooftop with a SWR meter. A 1:1 SWR dip was obtained on 21200khz with a SWR < 1.5 throughout the band at roof top level. Make sure the antenna is not touching the roof while tuning. the sagging also matters for precise tuning. Once the antenna was put on the tower, the SWR 1:1 point moved upto 21260Khz confiming the good old ham suggestions.
Performance
I was amazed with the performance specially the gain. I was able to work the weak (55) Dx stns from Europe with only 100W in a very bad condition (20th April 2003). Other side was using linears to get to me. This is a typical performance of a well designed yagi. I wan’t even hearing those weak signals with my G5RV or 20m yagi. The F/B was also excellent. I got the benefit of all the trouble of fixing two 20ft booms together for putting just 2 elements more.
On the 2nd day after putting the antenna up, I worked W1ZY Bill with 100W. He recorded my audio into some MP3 files and sent to me. Here they are. See how good the signal in USA is.
