Topband: Inverted L

[Milt, N5IA]

----- Original Message ----- 
From: "Guy Olinger K2AV" <olinger at bellsouth.net>
To: "Gene Smar" <ersmar at verizon.net>
Cc: <topband at contesting.com>
Sent: Friday, February 12, 2010 7:49 PM
Subject: Re: Topband: Inverted L


I had forgotten about the insulating of the parasitics on the F12
stuff.  He would just have to remove the slit plastic tubing (slit pvc
water pipe) and tighten the element mount U bolts directly on the
parasitic element.  No extra flashing, connections, etc needed.  If he
doesn't remove the slit tube and loads up the tower, QRO RF will flash
over the plastic any way.

I have a C31XR and will have to do the same thing if I load my 76' tower.
-------------------------------------------------------------------------------------------------------
-------------------------------------------------------------------------------------------------------

NOT SO!!!

I have constructed this type of installation for other hams.  One is an 80' 
length of Rohn 25 with the base elevated 40' AGL.

The 80' is topped out with an F-12 model C4XL which puts it at 120' AGL. 
The 160 vertical is series fed and has 2 dozen 1/4 WL elevated radials 
sloping down to an average of 10' AGL at their ends.

The 160 Meter energy is choked off the feed lines and rotor cable for the 
C4XL at the insulated base by coiling 30 turns of 6" diameter in each line.

By hanging a 75/80 Meter double extended Zepp off the end of a wooden Xarm 
at the 100' level, this single structure is a very high performance antenna 
system on all bands from 1.8 mHz to 29.7 mHz with the exception of 30 
Meters.

My point in relating this is that the parasitic elements of the C4XL were 
not modified and grounded.  There has never been any flash over at full 
legal limits on Topband through HUNDREDS of hours of contesting and casual 
operation.

If you remove the slit PVC tubes you will be subjecting the aluminum 
elements to stresses that they were not designed to receive.  The original 
U-clamps will be of the wrong diameter and will not fit around the elements 
correctly, compressing from the top only.  If you change to smaller size 
U-clamps to fit the element you will have to redrill the element mounting 
plates.

Too much hassle and posssibility of something going wrong, for a 
modification that does NOT need to be done IMHO and my real life experience.

YMMV.  Milt, N5IA