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YU7EF 2M13EL

Here is the design data from POP YU7EF based on the boom layout and element sizes I gave to him.

After receiving the design from Pop, it was then up to me to work out how I was going to feed the yagi. My previous yagi suffered a breakage through an element hole so I wanted to create a heavy duty boom that also had a low profle feed system to reduce wind loading. The feed system shown is a based upon a commericial feed system available from Directive Systems. I am grateful to them for their slimple but slick BALUN and bracket ideas (their feed designs were for T matches on K1FO yagis). You can buy the assembled feed system from the web site as "Spare parts" for their K1FO yagi's

On the example shown below, I slid a full length of 28.5mm tube inside the 32mm tube and left just the required 1.5M out one end to create the 8.5M long boom needed for this design.



Here are a random selection of photo's that show my first mock up of a folded dipole feed for a 13 YU7EF yagi on 144 MHz.

The results were a staggering VSWR of 1.1:1 at 144.5 MHz

rear of feed

Looking towards the front of the yagi, the white block is to support the folded dipole to ensure it can withstand a good nudge from a bird landing on a tip of the dipole.

The black hair pin is non tinned UT141 hard line coax simply painted black to preserve it in the weather.

side of feed

Side view of the feed showng the UT141 hard line and N socket bracket

close up side view

Close up of the feed point showing how it all comes together.

close up top view

Yes that is a rawl plug in there to keep the ends aligned. It is amazing what you find in the junk box when a need arises.  

All the solder joins still have their residual flux on them at this point as I was in a hurry to get the photos (late afternoon)
 

close up rear view

Rear top view, showing the link from the centre pin to the feed point and the terminations of the UT141 4:1 BALUN.

close up, other side

Other side view of the feed, all details are symetrical except for the center pin link from the coax socket
 

side view of support block

Side view shows the under side insulator of the dipole which was fashioned from some very tough black plastic (www.dotmar.com.au) called polystone.
 
 support block, side view
Another view of the folded dipole supports and feed.
 
 looking along the boom
Again looking forward along the boom (slightly more of a close up that the first image in case you were wondering)
December  2010 - VK5PJ
Details of building the feed point