[TowerTalk] 80M antenna wire size

[jimlux]

On 1/7/20 10:36 AM, Jim Brown wrote:
> On 1/6/2020 5:47 AM, jimlux wrote:
>> On 1/5/20 7:11 PM, Jim Brown wrote:
>>
>>>
>>> What I HAVE done (about ten years ago) was to add a second #10 THHN 
>>> to my Tee vertical for 160M, spaced roughly 8-10 inches from the 
>>> first, wired in parallel top and bottom. The vertical section is 100 
>>> ft. The measured result was to approximately double the SWR bandwidth.
>>
>> So, going from l/d  of 12000 to 120 -> that's a big, big difference, 
>> and the change in SWR bandwidth would be expected.
> 
> Yes. And this technique is probably older than I am.
> 
> 

I wonder when the theory was developed, as opposed to empirical 
observations.  I'm sure that empirical observations (1910, 1920) showed 
the bandwidth increase (as all of you running a flattop T antenna from 
your Alexanderson alternator on Straight Key Night did).

There's a picture of an "amateur station" from 1922 on Wikipedia using a 
cage T. So, Jim, I think you're right, unless you're in your late 90s.

https://en.wikipedia.org/wiki/T-antenna

So people did it, probably because it worked better, but I'll bet the 
"why" didn't come until the 30s and 40s.  Certainly, by Schelkunoff's 
and Hallen's papers in 1940s, the theory on the l/a ratio was well 
developed.

(OK,plunging down a rabbit hole.. Pocklington, in 1897, derived the 
electric and magnetic field equations for a "thin wire" and they include 
the length (l) and radius (a).  John Strutt (better known as Lord 
Rayleigh) complained that Pocklington didn't solve for a ring, so he did 
that derivation.

So I guess that folks did know about the "impedance bandwidth" effects 
of wire radius (or, at least could show the effects) at the turn of the 
19th to 20th century.  Whether Marconi, and other radio pioneers, 
actually paid attention to Proceedings of the Royal Society or Annalen 
der Physik is another question.


Next time someone asks me about how NEC works, I'll just point them to 
Pocklington's paper.<grin>

https://archive.org/details/proceedingsofcam9189598camb/page/324

H.C. Pocklington, "Electrical Oscillations in Wires", Oct 25th, 1897, 
Proceedings of Cambridge Philosophical Society.

Fascinating stuff in that volume.. Townsend on electrical properties of 
gases. Faraday vs Kerr rotation. UV photoelectricity.