[Moon-net] YU7EF 70cm antennas

[on4dpx Kenny]

Hello everyone , 

 

Being curious about the way of YU7EF low noise antennas I decided to build
one of his designs ( 13elem 70cm ) to see how these antennas act . 

Before cutting and drilling the antenna went to several simulations to check
several parameters . 

 

The first thing I noticed was the narrow bandwith of the antenna as well as
the intrinsic behaviour . 

 

As suggested by YU7EF the antenna could easly being fed with a folded dipole
so I went for the folded dipole . 

Once the antenna was builded and assembled I noticed currents on the
feedline that heavly influenced the SWR , measuring and adjusting didn’t
solved the problem , so I went for another solution . 

 

The T match showed the same problem , using a split dipole was useless
because of the high amount of ferrite beads that would be needed , but I did
tried the split dipole with a ¼ wave choke , same problem as above 
 

 

I finally decided to redesign the antenna to be able to use a folded dipole
without a balun , such as being used by F9FT . Therefore I lowered the
feedpoint impedance to somewhat 13 Ohm and measured it again . 

I did noticed a good match and absolutely no cable currents but the
simulated dimensions where not like the builded antenna , although the
measured gain and pattern where about the same as simulated . 

 

I builded several other antennas from well known designs up to my own
designs but never came to such problems as with this design . 

 

I was wondering if someone ever builded this antenna or others of YU7EF 70cm
designs ? 

Perhaps many designs live on computer or paper but what about real life
tests ? 

 

Most probably antennas with a very small bandwith compared to their
operating frequency suffering this problem . 

 

Any reply or suggestion would be highly appreciated . 

 

Best regards,

Kenny ON4DPX