[600MRG] Loading coils....

[Edward R Cole]

Ken,

I am no way an expert on HF antennas, but there are many ways to load 
a short antenna.  Your base coil is adding inductance in series with 
the coax line which is grounding the base end of the coil at the 
tuner if it is not grounded before reaching the tuner.  Hopefully you 
are using a good ground on the tuner.  Your tuner probably is adding 
inductance as well.  The coax line is part of the antenna since it is 
not grounded at the coil.  You mention a 40m trap which I assume is 
transparent below 7-MHz.

I feed an inverted-L which is basically a 43-foot high vertical with 
a long top hat (two 122-foot wires separated 2-foot but connected at 
both ends electrically).  That make it possible to run with a smaller 
base loading coil.  My coil is grounded on the far end and I tap off 
the coil about 2-1/2 turns above the ground end and connect coax.  I 
use no tuner as the coil is tuned for resonance and the tap for 50-ohms.

Be interesting to hear others comments.

73, Ed - KL7UW

At 08:44 PM 12/18/2014, Kenneth G. Gordon wrote:
>OK. I just realized that think I may have a misconception here about
>base-loading coils for verticals.
>
>I have a 55' tall vertical, which was originally designed for the 80 and 40
>meter ham bands. It has a combination trap/loading coil at the 33 foot level,
>so that the antenna acts as a 1/4 wave antenna on both 80 and 40 meters.
>
>I feed it with 50 ohm coax, and use a home-brew antenna coupler at the
>transmitter end to load it on all bands, including WARC bands.
>
>It works very well, considering that it is a vertical.
>
>Furthermore, it is the only antenna I have.
>
>Last year, I added a base "loading coil" to it so I could operate the antenna
>on 160 meters.
>
>I also calculated and bought the necessary "stuff" to make a base-loading
>coil for 600 meters.
>
>Now here's my confusion: when I used the base-loading coil on 160 meters, I
>connected one end of the coil to the antenna, and left the other end
>"floating". I.e., not connected to anything.
>
>Then I tapped down on the coil in the direction away from the antenna until I
>was able to obtain a 1:1 SWR on 160 meters.
>
>This worked quite well, and I managed to work Europe twice with this combo
>and 100 watts on that band.
>
>So, what was actually happening?
>
>What is confusing me is that I THINK I recall seeing base-loading coils
>added to verticals, like for a car, but the "far" end of the coil is 
>grounded, and
>the coax was connected to a tap somewhere above the ground point.
>
>This, to me, means that the coil + antenna must FIRST be resonant at the
>operating frequency, and THEN the tap for the feedpoint must be chosen to
>match the coax impedance.
>
>So, what was happening when I did NOT have the "other" end of the coil
>grounded, yet the system worked very well?
>
>BTW, it took only about 2 turns of a 4" diameter coil wound of #12 wire on a
>ceramic form to achieve the match.
>
>I now suspect that my antenna coupler was providing the necessary extra
>inductance to enable the match.
>
>In addition, I cannot find my ARRL Antenna Book right now... :-(
>
>Ken W7EKB
>
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73, Ed - KL7UW
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