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[TowerTalk] C4XL Driven Element Placement

To: <>
Subject: [TowerTalk] C4XL Driven Element Placement
From: (
Date: Wed, 24 Dec 1997 13:25:37 -0800 (PST)
Good morning, Mike.

Thanks for the opportunity to respond to your Tower Reflector comments. 

Two important subjects here:
        * One is the UPS situation on your boom.
        * The other is the 40 mtr portion of the antenna and the process to 
follow should be useful for anyone putting up various antennas where strange 
results occur.

The boom was replaced as quickly as possible, after a very difficult time 
with UPS. As we told you on the day it was shipped, we sent it to you 
without any authorization from UPS of replacement value, nor UPS covering 
the next day air shipping expense. To date, we have received nothing from 
them, not even a promise, so the entire expense is out of this company.

The pictures you sent via e-mail were viewed, after checking for viruses. 
This took some time, as this system is not set up to do that. The photos are 
from such a distance that there is nothing useful that can be seen. They are 
apparently scanned photos and are also very grainy. I used some graphics 
software to enhance them, but met with little success.

The comment about the 40 mtr being properly resonant on the ground and then 
moving to 4.26 MHz in the air indicates there is something dramatic 
happening that is out of the ordinary. This is the first you have mentioned 
this to us, so let's go through a logical process.

Most important to know is that the 40 mtr elements are not possible to 
resonate at 4.26 MHz. The bottom of their tuning range is about 6.850 
MHz. So, when you see the antenna "resonance" moving down to 4.26 MHz, 
it indicates something major (external to the antenna) is coming into play. 
Also, common sense will tell us initially that even if the 40 mtr driver 
location is off by yards, it will not cause such a situation as this.

To trouble shoot this problem, let's go through this process:
A)      Helpful to understand what "on the ground" means. Does this mean the 
        tower is down, or the antenna is a few feet off the ground?
        A1)     If it means the tower is cranked down, then the most the 40 
                mtr will shift is 10-20 kHz to its final height. This is an 
                upward shift, not downward.
        A2)     If it means a few feet off the ground, this is not an   
                acceptable height for tuning a 40 mtr antenna and is covered 
                in the manual. However, even in this case, the 40 mtr will 
                not shift downward to 4 MHz, even if this is the case,  
                without something else being involved.

B)      Since we know the issue is a dramatic downward shift, out of the 
        possible tuning range of the 40 mtr elements, something else is 
        happening. We know this because of two reasons:
        1)      The apparent resonant frequency when the tower is up is 
                so far removed from the possible range of the 40 mtr 
                elements as to not be possible without an external 
        2)      The shift is downward, whereas an antenna will normally 
                shift upwards as the tower is raised.

        From several years of working through "strange occurances", things 
        that I have seen more than once before are (not in any particular 
        B1)     Does the feedline possibly have a worn jacket and coming 
                into contact with the tower when it is up?
        B2)     Is the antenna selector on the right antenna?
        B3)     Is the antenna (40 mtr) coming into contact with anything 
                when it is up?
        B4)     Is the antenna (40 mtr) coming into close proximity with 
                something conductive when it is up?
        B5)     Does the apparent resonant frequency (and VSWR) vary as the 
                antenna is rotated?
        B6)     Is there another antenna on the tower, such as a wire   
                antenna, that is not up unless the tower is up?

OK, that should do it. My apology for being out of the office a couple days 
this week. Some kind of cold/flu bug has been going around and got to me. I 
have been coming in anyway for short periods in the morning to not get too 
far behind on all the e-mail.

Hope you have an enjoyable Holiday Season and a terrific New Year!

Have a good day and 73,
                        Tom, N6BT
                        Force 12 Antennas and Systems
                        (Home Page )

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