2SA13_Coax_Dipole

2SA13 antenna (Coax-dipole)

In my current EME antenna's I use the 1:1 Baluns that are well documented by ON4KST in his 6 mtr. Yagi, but for a try, I modified the feed towards the dipole in an attempt to reduce the losses in the Balun. The feed to the dipole can be direct in case one uses so-called 'Coax-dipoles'. The below pictures shows the original Balun constructed from the two pieces of different length coax.

This is believed to have losses like in the order of 0.2dB. Coax is RG213, capable (and tested)

with QRO...It also is believed to influence the radiation pattern and some HAM's found that a

5wl antenna acts as a 4.5wl antenna because the first directors were no longer in the main beam.

When using 4 yagis, it a waste of a lot of aluminum (2wl of boom material not functionally).

How a coax-dipole must be build is not decribed in detail here, just my implementation in form of a few pictures will show how I solved it. Please google for 'Coax-dipole' and somewere you find a nice page in were for VHF this is descibed.

Opening 10x1mm tubing for dipole for inner of H2000 cable to pass through.

Opening dipole for inner of H2000 cable to pass through.

End of one dipole half, inner of H2000flex cable bend prior to mounting

Brass M5 bolt and nut to connect H2000flex inner to dipole end. Other end of dipole identical.

Inside the box, inner of H2000flex jumps from one dipole-half via hole

to the other dipole-inner. It's not connected in the middle. It serves to balance

the current on the dipole. Mind the N-chassispart is not connected yet.

New dipole ready to be mounted on boom. Very poor reflection-figure now, but that is expected...

With new dipole mounted on boom, reflection is an amazing 60dB! This of caorse after hours of

tweeking the dipole-length, first director and the distance between the two.

Test setup with Coax-dipole in backyard...Feeder output already choosen to be at rear

of boom. This is a choise to be able to convert the yagi into a H/V-yagi later. With that,

the feeders for Horizontal and Vertical must leave the antenna at the rear towards the

two 4-way combiners.

End of dipoles have been ancapsuled with Hot-melt glue and covered in tape.

This will prevent moisture to come to the short-circuits were the H2000flex inner

is connected to the tips of the dipoles.

IMPORTANT:

After some more study the idea to use coax-dipoles is abonded. It is adviced still to use a Balun in this system, even others say it would not be needed. To be sure I now keep using the orginal 1:1 Balun described by ON4KST. Who is willing to try the coax-dipole idea in his EME-system and report his findings to me? Is the anttena pointing in the direction you want or is there offset in AZ/EL due to current on the outer of the feedlines....???