LOG periodic antenna design - qustions

[KeepItSimpleStupid]

I have what looks to be a log periodic antenna design and I'm really confused with the connection to the longest element. Take a look here: **broken link removed** It's not this antenna. It is a VHF/UHF antenna.

For the most part, there is a square boom and each "half" of an element is connected in an array like structure, a connection for one side and one for the other side with an aluminum strap.

So picture, properly spaced elements a through whatever.

(top)
element a1 or (what I might call 1/2 an element)
Bus bar a1
insulator a1
aluminum tube (Boom)
insulator a2
Buss bar a2
element a2
(bottom)

Rivet 1, goes though all of the a1's and rivet #2 goes through all of the a2 sections with no connection to the square aluminum tube.

That's fine and dandy UNTIL we get to the longest element, then things get really wierd and don't make ANY sense at all.

This is where the antenna manufacturer takes one huge 3/16 rusty rivet and connects everything together and mounts the rivet head on the bottom. The connections to element a1, Buss bar a1 and bus bara3 and element a2 is a solid connection.

I enlarged the hole in the system from 3/16 (0.1875) to 5.1 mm (0.196) almost negligible to fit a 5 mm screw.

The thing is, that connection can ground the boom based on corrosion and shear luck (OEM and my version). Me thinks that the holes in the aluminum tube should be much much larger than the rivet to avoid that connection. The grounded boom should be Earthed because it is connected to the mast.

How did I run across the possible problem? I wanted to replace the longest element because it was severely bent.

I did make a special screw to insulate the boom. Is this the right way?

 

[vincehhh]

If I read this right the both of last elements (largest) are shorted and to ground.

From my understanding this is the way it works as the last element pair are acting as a reflector to the next and are normally grounded.

For a log periodic from my understanding 3 pairs are active for each frequency to be received.

the middle is half wave tuned
the one bigger acts as a reflector and the smaller one acts as a director.


And thanks for the link I am considering making a log periodic myself.

 

[KeepItSimpleStupid]

Thanks.

The antenna is this one. https://www.google.com/url?sa=t&rct...McktWJhsaTuWaEw&bvm=bv.56343320,d.cWc&cad=rja



Right now, the 8 or so elements from the inside of the paper is mounted on the mast. It was initially on a test mast on the ground.

There is a strap that runs on the top and the bottom of the boom. So, the elements facing the inside of the paper are connected to one strap and the elements facing out of the paper are connected to the other. This will eventually become a 75 ohm down lead.

So, with the left and right sections of the antenna separated, the right section was infinite to the boom and the left section was shorted to the boom at the longest element.

That boom shorted connection would be very iffy.


Here are the instructions:
https://www.google.com/url?sa=t&rct...D98h0NNr5DXMvAghU_-2QWA&bvm=bv.56343320,d.cWc