Topband: Phasing Inv.L question

[Tom Rauch]

> I have 2 inv. L's up spaced 134" apart ....They are 150' long with
> approx. 75' vert. 75' horiz.....the horiz. parts are almost parallel. I
> have ON4UN's new book and have read it numerous times regarding phasing
> but still have a question. Should I match each inv.L at the feedpoint to
> match the 50ohm coax going to it for the phasing lines or do I feed each L
> with the appropriate length coax and match at the center feedpoint (where
> the delay line is) or do I need to do both? 

You must match at the common point, not at the inverted 
L's....unless you really know what you are doing with transmission 
lines and phasing systems.

You are also headed for trouble if the inverted L's are NOT exactly 
or very near 1/4 WL long.

Here's why for two element arrays:

1.) Identical antennas that are fed at the CURRENT maximum require equal
currents in each element, not equal power..not equal voltage

2.) Identical antennas that are fed at the voltage maximums require 
equal voltages at the antenna feedpoint. Not equal current at the 
feedpoint, and not equal power.

If the elements are neither current fed, nor voltage fed, you will have 
a "mess". Maybe you will get lucky, maybe not.

Now move back from the feedpoints, and follow this logic.

1.) If you feed current fed antennas through odd-1/4 wl lines, the 
end of the feedlines require equal VOLTAGE to drive the antennas 
properly. Not equal power and not equal current.

2.) If you feed these same antennas through 1/2 wl lines, they 
require equal currents into the feedline.

Now a system can be designed where the antenna is fed neither at 
the current or voltage maximum, but it is more simple to just "go 
with the flow" and current feed your L's by making them 1/4 wl long 
(resonant) and using 1/4 wl or odd-1/4 wl lines to a phasing system 
that drives each line with equal voltages.

Check out some of Roy Lewallen's articles on this subject, and do 
some modelling if you can. Remember a delay is only the electrical 
length long in degrees with approximately equal voltages at each 
end when it is operated with a 1:1 SWR. With that in mind you 
must plan the system, or be very lucky. 

Once again a hybrid does not guarantee.... or even lean you... 
towards correct results. They key is in the rest of the system.

> the L's at all...170' or 134' etc......I have,at this time, 30 100'
> radials on each with more to come....The array is 250' from the house. I
> just happen to have a length of 3/4 catv that I could use or should I
> stick with the 213 I have there now? Thanks for any input... Happy

Use whatever you like. It will make little electrical difference as long 
as you take care of the 75 ohm cables mismatch problem 
somehow or someway at the rig. Myself, I'd just use the 213 if it is 
good shape.

73, Tom W8JI
w8ji@contesting.com


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