[600MRG] A dilemma....

[Kenneth G. Gordon]

OK, Folks, I need some ideas here.

First, "The Situation".

Due to on going construction of an addition to our home, I had to take down my only antenna. 
That antenna was a trap vertical, containing ONE trap at the 33' level, and a "stinger" 21' long 
above that for an overall length of 55', and it is fed with 50 phm coax.

The antenna exhibits an SWR of under 2:1 over all ham bands, except the high end of 75 
meters, and the lowest end of 10, excluding the WARC bands. 

Even so, I used it on all bands 80 - 10 including WARC bands with a home-brew antenna 
coupler. I could add a 3 or 4 turn coil at the bottom and could achieve an SWR of 1:1 through 
the coupler on 160 meters, but only for about 10 kHz, then I would have to adjust the tap on 
the base coil.

Since that antenna amounted to 1/2 of a single-trap-dipole, with the other "half" being the 
"image" antenna below the vertical (helped along by several 66' long radials), I had the idea 
of constructing 1/2 of a 160 - 10 meter trap-dipole and installing it as an "end-fed sloper with 
counter-poises" with the "far" end in the top of a 107+ foot tall Grand Fir tree in our back yard.

Since the overall distance from the lower attachment end of the proposed sloper, to the top of 
the tree amounts to about 137 feet at an angle above the ground of about 65 degrees, and 
the overall length of 1/2 of a 160/80/40 meter trap-dipole I found on the ARRL's website in an 
article is a little more than 62 feet long, I thought that by adding a 160 meter trap, I could 
(maybe) load the full 137 feet on 630 meters too.

The big trouble is that although calculating values of components for the traps is not too 
difficult, I have not yet found any way to calculate the lengths that the wires should be 
between, or AFTER the traps.

The traps act like loading coils on the band below which they are "tuned" for, thus shortening 
the wires required to resonate the antenna at the lower frequencies.

For instance, the 40 meter trap inductance acts as a loading coil to make the following length 
of wire necessary to resonate an 80/40 meter trap dipole or vertical at 80 meters shorter by 
around 30 percent (21 feet vs 33 feet), and the effect appears to be cumulative, since, when 
adding a second trap tuned to 80 meters, the length of wire between the 40 and the 80 meter 
traps falls to 11 feet (from 21 feet) to make the antenna resonate at 80 meters, and the 
length of wire AFTER the 80 meter trap required to resonate the antenna on 160 meters is 
only 18.3 feet.

So, how the heck does one calculate what the length of wire should be between the 80 meter 
trap and the 160 meter trap when one adds that 160 meter trap in order to use the entire 
length on 630 meters?

The inductances of the traps is, or can be, known, so this may help.

But this brings up another point: apparently, it is the RF impedance of the LC combo at the 
operating frequency, NOT the resonance, which makes all this work together, but how does 
one calculate that? 

I'm stuck at this point.

I suppose I could figure it out "emprically", but that takes a LOT of effort and time, which I 
don't feel I have at the moment.

I have searched the web for several days, and have found a lot of useful websites with JAVA 
enhanced calculation "engines" but none, so far, provide the info I need.

Anyone?

Ken W7EKB