[600MRG] A dilemma....

[Brian, WA1ZMS]

If memory serves....there was an article in QEX many years back that addressed this topic.  The take away is: that along the length of a trap dipole you need to factor in the effect of the impedance changing. It has to. Voltages and currents are different at each location. Thus it becomes a more complex problem than just a simple LC tank that is resonant at freq(a). The trap will take the place
of several degrees of phase shift "away" from the lower freqs that you want to keep traveling down the rest of the wire. The solution requires almost simultaneous equations to be solved if you get more than say 3 bands involved.

I know I'm not giving this the best explanation it deserves. And guys like N6LF can "leave me in the dust" when it comes to antennas so take what I say with caution.

If I or anybody else finds the article please post it. It's one I should have scanned into pdf at the time I read it.

-Brian, WA1ZMS & XSH/31 in Va
iPhone

> On Aug 31, 2015, at 5:33 PM, "Kenneth G. Gordon" <kgordon2006 at frontier.com> wrote:
> 
> 
> 
>> On 31 Aug 2015 at 17:33, Marten T Beels wrote:
>> 
>> Ken,
>> 
>> This may be a slightly different thing then what you're looking for, but
>> based on the following idea a 5-band dipole can be built with one set of
>> traps.  The idea is not operate the traps near resonance, but far from
>> resonance and use the resulting capacitive or inductive reactance to 
>> resonate the antenna.
> 
> Yes! That is exactly what I had in mind, but could find no means of calculating that.
> 
>> The best that I can find is an article by Yardley Beers (W0JF) from 
>> August 1987 that refers to several equations in the appendices.  I can
>> find the original article online, but not the appendices.
>> 
>> http://www.k0to.us/HAM/Dual%20Dipole/Beers%20-%20dual%20band%20dipole.pd
>> f
> 
> OK. Thanks. I'll try to track those down.
> 
>> If you know the inductance of your traps, you could calculate the 
>> reduced length of the lower frequency antenna with something like
>> this:
>> 
>> http://www.see.ed.ac.uk/~jwp/radio/software/loading.html
>> 
>> or this:
>> 
>> http://www.m0ukd.com/calculators/loaded-quarter-wave-antenna-inductance-
>> calculator/
>> 
>> (same formula).
>> 
>> Marten
> 
> Thanks, Marten. I'll give those a shot.
> 
> Ken
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