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Subject: [TowerTalk]
From: (Frank Norton)
Date: Sat, 07 Jul 2001 17:08:58 -0400
Tom w8ji makes some interesting but uninformed comments about the Tennadyne 
feed  system.  The booms are in fact the feedpoint for the antenna and the 
collins balun belongs at the transition from the unbalanced coax line, to 
the balanced line necessary in any log periodic construction. The parallel 
booms substitute for the balanced line and make the antenna much more 
efficient. The potential of the lower (or upper) boom is the same as that 
of the feed line.  The booms are simply aluminum feedline, they are not 
radiators, just balanced line.  The idea that the balun at the feedpoint 
forms a dead short is simply untrue when you study the construction if that 
were true every antenna forms a short at some point because the shield 
grounds the antenna.  Whether it is a log, a vertical, or a yagi.

By the way you do not have to strap the coax to the lower boom if you don't 
want to, it can drape down or use separators if you like, but they are 
unnecessary.  It is true that you have to be careful not to have any barrel 
connector touching the boom but a single layer of tape is sufficient 
insulation.  You can also add a RF choke if you like, again it isn't 
necessary but it would prevent spurious emissions from the unbalanced 
coaxial feedline from the choke to the antenna.

I own 2 models of Tennadyne LPDA's (1 HF, 1 VHF) and both work 
wonderfully.  No RF on the coax either, hi hi!  I have also owned The 
Sommer hybrid log, as well as the other generic brand, as well as F12 C4E, 
and other yagis but none performed with the pattern and forward gain of my 
T-10.  I have never owned any other VHF log so I will not comment on others 
in that field.

Chuck designs and sells antenna systems to military and civilian entities 
all over the world, I am sure they would note any problems that I have 
not.  My advice is to examine the theory of Log Periodic Dipole Antenna 
construction, I found it fascinating.  Once you have, I believe that you 
will find that no one exceeds the quality or efficiency of Tennadyne.

I respect Toms idea but it simply isn't true if you study the construction 
of the Tennadyne LPDA.  You can have my pair of Tennadynes when you pry 
them from my cold, dead, fingers as the saying goes.  (No, I am not related 
to Chuck, I don't get paid, or a discount etc......)

Thanks for your time.  Please no flames, this is meant in discussion not 
attack of any other brands.

Excerpt of comments to save bandwidth:
W8JI wrote: " That means the shield leaves the antenna with voltage on it, and
also that the balun at the feedpoint is electrically shorted and does
Assuming the shield connects to the lower boom and the coax
runs along that boom, the correct location for the balun is at the
exit point where the cable leaves the boom and goes to the tower.
Most certainly not at the feedpoint! "


Frank, kb8xu

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