# Re: [TCML] Tesla Coil + Transmitting Antenna ?

I left out the bit about the 'axial mode' since this is not a microwave discussion. Kraus was a ham first, then engineer and scientist, so his grasp of the subject was profound. Although outdated by now his Antennas book should be on the bookshelf of anyone interested in the subject.
```
```
Even though the '1/4 wave myth' seems to have been started by the great man himself he should have understood better and maybe his statements are misunderstood. Anyone looking at the pictures of his big coils at Colorado Springs should realize that the total wire length was very small compared to the wavelengths he used, which were typically a couple of miles or more. Myth and hearsay die hard!!!!!!
```
Electronic Battle wrote:

```
```Hello

One point to note is that the helical antenna model we're talking about
(when we ask if the TC secondary is like an antenna) is a normal mode
helical antenna (NMHA) as opposed to an axial mode helix. In the former
case the radiation pattern is broadside firing and in the latter case it
is an end fire (i.e. the NMHA looks a bit like a monopole -
omnidirectional pattern in the azimuth plane i.e. normal to the axis -
and the axial mode squirts all of its radiation out of the end i.e.
along the axis). John Kraus was one of the joint discovering antenna
researchers of the helical antenna and hence is a useful reference source.

However, the TC secondary is so electrically small, the radiation
resistance (that part of the antenna equivalent circuit which accounts
for power lost to the far field) is swamped by the loss resistance
(conductor loss, predominantly).

The NMHA is often modelled as a short dipole in between each
loop. The turn-to-turn spacing of the TC secondary sets the
dipole length and the loop circumference is the TC secondary
circumference. At the usual TC frequencies i.e. <1MHz, typically a few
hundred kHz where wavelengths are in the region of a kilometre, you can
see that the TC will look to be very very electrically small and a poor

So - there is a strong near field (E and H) around the TC but not much
far field (the far field's the bit that radiates away as an
electromagnetic wave, E and H fields in-phase in time, but  phase
quadrature in orientation, capable of dissipating power in a distant

On 07/06/12 05:20, ED wrote:
```
```This configuration is usually called a 'helical antenna' and is very
inefficient if the length is short compared to a wavelength.  That's
true for every TC I've ever seen described.  Look up 'helical antenna'

miles wrote:

```
```To comment on the post made earlier by Matt Siri

I have always wondered if the secondary of a tesla coil has any
interesting antenna properties, as well as simply acting as the high
voltage end in an pair of mutually coupled resonant LC circuits. I
believe, in the transmitting dipole/quarter antenna case, the length
of the secondary tube, not the length of the wire wrapped around the
tube, would be the interesting variable.

Miles
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla

```
```_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla

```
```
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla

```
```_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla
```