15m 6 element yagi on 40ft boom – April 2003

The project of the ‘3 el 5 band quad’ was not a tremendeous sucess as I wanted it to be. I wasn’t too happy about the back lobes on certain bands and also the foward gain compared to the G5RV.

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 foward gain. The selection of the 40ft boom is another first time experiment, which turned out to be a great sucess.

 

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.