[Antennas] Broadbanding an antenna...

[Ray]

Richard,
Thank you for taking the time to compose the nice reply.

I'm well aware of the use of a "matching" coil at the bottom of a 
typical vertical or mobile antenna.  I have a home brew coil on my 500 
watt HF mobile antennas.  I've been using it for years.

But this is not the same thing as the shunt L-C network that W7XC was 
using.  He used the base matching coil for base impedance matching, and 
in addition an  L-C resonate network for frequency excursions away from 
resonance.  The shunt network  was resonate well above 160 meters.  It 
was expressed in the article as purposed to compensate with an opposite  
reactance curve to the reactance that occurred as he tuned away from his 
best matched point.

FYI:  The impedance of the base of the antenna doesn't really change 
that much as you very frequency over a given band, but the reactance 
does.  In fact on my mobile, I use the same tap settings on the base 
matching coil for 40 and 20 meters on an 8' center loaded antenna.

I have a 3000 plus book library and am an avid reader of related 
articles.  I'm just surprised I've not seen anything else published on 
the same subject.  I was hoping someone else may have seen something I 
had missed.
73,
Ray, W4BYG

On 5/22/2012 2:43 PM, Rick Karlquist wrote:
> This is pretty much that same technique that has been used with
> screwdriver antennas since their inception.  You will notice
> that certain screwdriver models have a base that cleverly has
> a helical groove cut into it, forming a fairly low value shunt
> inductor.  If your screwdriver doesn't have this, you can attach
> your own coil, which is what I did for my Hi-Q screwdriver.
> I haven't seen any articles describing this approach either,
> but considered it "common knowledge" or something that any
> serious investigator would eventually figure out on his own.
> Fairly obvious how it works once you see it.
>
> Anyway, it is a really nice technique that is applicable over
> much more bandwidth than just the 160 meter band.  In a screwdriver
> application, it is good from 160 up to 17 meters, using a
> 102 inch CB whip on top of the 4 foot screwdriver base.
>
> I don't know who invented this, but I suspect it was someone
> involved in the early history of screwdriver antennas.
>
> Notice that this technique only tracks the resistive portion of
> the antenna impedance.  The reactance cannot be "tracked" by
> any fixed component configuration, hence the need for the motor
> driven inductor in the screwdriver.
>
> Rick N6RK
>
>
> Ray wrote:
>> Charles Michaels, W7XC, (someone else has this call now), designed and
>> built an interesting network to successfully broadband his short 160
>> meter vertical.  He called it a "Load Tracking Network".   It was
>> published in the April issue, 1992, QST.
>>
>> I've not seen any other reference materials or articles on his
>> approach.  It involved designing a series inductance plus a shunt "L-C"
>> network.   The shunt network resonated at about 3.4 Mhz thus had the
>> reverse reactance characteristic of what occurred as he tuned off of his
>> optimum frequency.   It seems like a valuable approach to broadbanding
>> and antenna.
>>
>> Has anyone else has expanded or written on such a "Load Tracking
>> Network" that it could be more easily utilized in other narrow banded
>> applications such as HF mobile antennas or other bands?
>>
>> Thanks for your attention.
>> 73,
>> Ray, W4BYG
>> ______________________________________________________________
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