2SA13 - 13 Elements 2mtr beam, length 8,30 meter

I`m not going to write much about this beam, because I only copied the design as much as possible from a existing one on the internet, See for full description and how to the site of OM PA2EXV.

Only differences in my design are the boom, it`s not made from round pipe but from rectangular pieces of alluminium. Middle section 35mm, next 30mm, then 25mm and on one side as last piece 20mm square pipe. Wall thickness 2mm.

Elements are not through,..but with insulated Poly Ethylene blocks fastened onto the boom

At the right the first piece of boom with radiator/reflector and two directors bolted onto the boom.

The driven element here is fed by a coax BalUn, like PA2EXV also describes on his pages, made from 2 pieces of RG213, neatly finished with some good quality heat-shrink tubing with glue in it.
And connected to a N chassis connector.



The first part of the beam also connected to a spectrum analyser, at the right a screenshot of it. Frequency still to low, needs adjusting when the complete beam is bolted together. I made the driven element 2cm to long so I still have plenty to adjust.


After I finished the rest of the boom time to put things together and make some adjustments, putting a ladder against the pergula so the beam can a bit look free into the sky and put the analyser onto it.

After some moving around with the driven element I could not get it perfect on a swr of 1:1 at a freq of 144.500Mhz, it`s also very narrow towards the high end of the band. SWR of 1:2 at 140 and 144.900Mhz.

Very narrow to the top end, as seen on the picture below measured ar a center freq of 144.300Mhz. Here the 2nd director is moved away from the 1 director (approx 8cm)

Measurement setup: Hameg HM5014-2 spectrum analyser, Mini-circuits ZFDC-101 directional coupler.
First I measured the coupling of the coupler, so I can use this in my measurements and calculations.
Max refelection measured on 144.700Mhz is around -72dBm, lowest point in my peak at the right picture.


I fiddled around some more with the length of the 1st director, I got the bandwidth a bit broader towards the higher freq. In combination with the moving of the 2nd director of around 4cm away from the first director I got a perfect SWR of 1:1, a bit lower in frequency as it should but I still have to adjust the length of the radiator.


To have a bit more freedom in adjusting the radiator I modified it by pressing in some brass threated sleeves. Put in some M6 bolts and I can adjust as much as I like to get the job done. Much easier then adjusting with a hacksaw to find out you made it to short. It works on 27Mc antenna`s, so why not here.


With the above modification I got it pretty well on frequency with a minimum SWR of around 1:1 to 1:1.1. Pretty close after fiddling around and measuring for about 2 full days.

Still have to bolt the support wire to the boom to support the weight towards the end of the boom. More work to come here to connect the LDF coax onto the boom and tower.



PA2MRX 2010