Re: [TowerTalk] Log Periodic Feed

[Kevin <kstover@ac0h.net>]

That is exactly what Tennadyne has in their manual.

They have you tape the coax to the bottom boom.

Now think about this. Would you tape the feed line to a dipole to one of 
the wires?
I'd hope not.

The better way to feed a hot boom log is to let the coax hang a foot or 
two, from the feed-point all the way back to the mast, with appropriate 
mechanical support, OR, feed it like Tennadyne suggests and have one 
killer common mode choke where the feed line exits the antenna. The 
coiled coax at the feed really does nothing. You need a high quality 1:1 
balun.
Look here. http://w8ji.com/baluns_on_log_perodic_antennas.htm


On 7/6/2016 5:25 PM, James Wolf wrote:
>   
>
> Continuing the discussion on how to attach the coax to the “hot” boom of a 
> Tennadyne T8 antenna.
>
>   
>
> As I assembled this antenna, I became increasingly confused and concerned about the feed 
> system.   With this log antenna, instead of running open feedline wires crossing over to the 
> elements, it uses two boom pieces and each is insulated from the mast and each boom is 
> “hot”.  The instructions indicate and show how to attach the feedline to the 
> bottom boom piece using a Collins type balun at the feed point which is at the forward end of 
> the antenna.
>
>   
>
> My concern is that of the coax shield separated only by the coax insulation alongside one of 
> the “hot” boom pieces would couple and cause radiation (phase shift) problems 
> with the antenna or at the very least radiate as it goes vertical down the mast.
>
>   
>
> Due to the element mounting method it is not possible to run the feedline 
> inside the boom to the mast.
>
>   
>
> Does anyone have any thoughts on why running the coax along the “hot” boom 
> would be an OK idea?
>
> And if not, how else would one feed the antenna?
>
>   
>
> Jim – KR9U
>
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>
>
>
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