We look at the magnitude of the impedance of an EFHW “antenna” for short counterpoise lengths.
Thanks to Jon AF7TS for the suggestion and discussions that led to this article.
In engineering we sometimes can not directly calculate a value, often when a “divide-by-zero” shows up, as when we try to calculate an impedance wiith a zero length element. However we can usually still tell what that value will be by sneaking up next to it and determining what it asymptotically approaches.
Continue reading Z of EFHW vs. “Counterpoise” Length
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A simple transmitter, transmission line, and an “End-Fed” antenna WITHOUT a formal “Counterpoise” – We add a loss-less choke at the feedpoint, tune out it’s inductance with a capacitor, and see why common-mode current on the coax shield is the SAME as without the choke.
From Part 1 and Part 2 of the “Current Flow Fundamentals for an “End-Fed” articles, we saw that common-mode current must always flow on the coax shield when we don’t use a formal counterpoise. And that the value of current on the “counterpoise” is identical to that on the “radiator” at the feedpoint.
In Part 3 we saw that it doesn’t matter what loss-less device(s) we put at the feedpoint – when we re-adjust our transmitter or tuner the SAME current flows common-mode on the shield as before.
Continue reading Current Flow Example for an “End-Fed” Antenna with a Loss-Less Choke
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Part 1 – A simple transmitter, transmission line, and an “End-Fed” antenna WITHOUT a formal “Counterpoise” – We will see why common-mode current must ALWAYS flow on the coax shield.
End-Fed Antennas have been around since the good ‘ol days and were once most popular. Yet for some reason, much discord still exists regarding the “counterpoise” – what its behavior is, or if one is even needed. Not all that surprising since the term “counterpoise” doesn’t seem to have a firm definition. Hopefully, we can figure out what’s going on despite the semantics, and deal only with easy to understand basic principles.
Principles like this from basic physics:
“…charge conservation is the principle that electric charge can neither be created nor destroyed.”*
Continue reading Current Flow Fundamentals for an “End-Fed” Antenna – part 1
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Part 3 – We place various devices at the feedpoint of an “End-Fed” antenna without a formal “Counterpoise” – We will see why the SAME common-mode current must ALWAYS flow on the coax shield just as in Part 1.
The typical “end-fed” generally has an impedance greatly different from 50 ohms, so it is rarely fed directly with coax, as losses on the transmission line will be undesirably high for lengths of coax greater than a few 10’s of meters.
Note the high loss on several bands when a 42 ft “end-fed” is directly fed with 50 ft of RG8x coax (yellow bars)* ===>
Continue reading Current Flow Fundamentals for an “End-Fed” Antenna – part 3
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The principles and projects described in this collection of GE technical articles from 1946 through 1963 are still perfectly understandable and relevant – enjoy!
Continue reading Classic GE Ham News
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In the course of my career as an EE specializing in Ultra Wideband radio, radar, and antenna hardware, the need often arises for a useful and easy to reproduce UWB antenna.
Continue reading Simple Ultra Wideband (UWB) Antenna – 200 MHz Bandwidth
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Here is a collection of some of James Millen’s early work in radio communication techniques.
Continue reading Classic Collection of Early James Millen
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A good reference on Sideband principles and techniques in this 1961 classic by GE and Ready Killowatt’s cousin Lighthouse Larry.
Continue reading Classic GE Sideband Handbook
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The principles and projects described in this collection of RCA technical articles from 1938 through 1968 are still perfectly understandable and relevant – enjoy!
Continue reading Classic RCA Ham Tips
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