Check out the manufacturers website, even their two footer is a 5/8

http://www.firestik.com/CatalogFrame.htm

Here's a gem from their FAQ section:

If you go back to the real basics like Maxwell's equations, or look at how antenna modelling code works, you find that radiation is fundamentally related to current flow and linear physical length. For the mathematicians amongst us that mean Idl.

That tells us that a 6ft antenna radiates like a 6ft antenna, no matter whether you base load it as a quarter-wave, a half-wave, a 5/8 wave or any other "wave" that the advertising department cares to magic up for gullible customers

It should also tell us that no matter how much wire we stuff into that 6ft length, by coiling it, meandering it, or any other method, it will still behave like a 6ft antenna.

The only thing we can change is how efficiently we force current into that 6ft length.

73,
Steve G3TXQ

Surely fractal antennas prove that theory wrong?

Gerry,

Why would you think that?

73,
Steve G3TXQ

I was always taught that there is "no substitute for a large amount of metal in the air".
Of course in those days we understood but, possibly, these days it needs to be changed to "no substitute for a large amount of metal in the air correctly used." and that 132ft of fine wire wrapped around a pencil is still only a pencil length antenna.

Cheers

Tony

I haven't made my mind up yet as fractal theory appears to turn accepted theory on it's head. I'm just asking your opinion as it conflicts with your last post in relation to cramming a half-pint into a pint pot for want of a better expression.

It's this large v small = negligible capture area difference, I struggle at times getting my head round.

Gerry,

Fractal antennas follow Maxwell's equations just like any other antenna; the only difference is that you have a complex pattern of elemental currents distributed in two (possibly 3) dimensions.

The important thing to grasp is that the total radiation is still accurately represented by the integration of a (large) number of Idl elements; so, where two similarly-sized currents are spaced a small fraction of a wavelength from each other and are flowing in opposite directions the radiation from them will tend to cancel, meaning you need more current for a given power radiated, and the radiation resistance drops. There's nothing fundamental about a fractal antenna that a modelling programme can't handle - it simply "number crunches" those hundred or thousands of small linear elements carrying different currents.

My earlier comment was aimed at single-dimension antennas, but the same principle also applies to two (or three) dimensional ones. For example if we had a small loop antenna of a given diameter, stuffing more wire into that same diameter - for example by helical winding around the loop perimeter - changes nothing except adding more loss resistance.

That's not to say fractal antennas don't have a useful place, but it's not because they are acting like a larger antenna containing the equivalent amount of wire.

Cheers,
Steve G3TXQ

I used to run a Radio Communications course for our newly-recruited graduate engineers - their university courses seemed to leave them woefully ignorant!

The real mind bender was to get them to work through the capture area of a 4ft dipole used on 80m; it works out at about 9,500 sq.ft

73,
Steve G3TXQ

At the other end of the scale, when I was a trainee, at a certain establishment, one of my roles was to show university entrants how to solder.

Cheers

Tony

Gerry,

One, or both, of the following thoughts might help the head stop spinning a bit.

1) We know an isotropic radiator is infinitely small, yet it has a gain that's only 2.15dB less than a half-wave dipole. So, in going from something a half-wave long to something that's infinitely small we've only reduced the capture area to 61% of what it was! That strongly suggests that capture area is not directly related to physical size.

2) Say we had a short dipole that had a radiation resistance R, and which picked up a signal of V volts. The maximum power we could extract from the dipole would be with a matched load of R, and the power would then be:
(V/2)^2/R = V^2/4R

Now let's halve the length of the dipole. We know it would now only pick up half the voltage: V/2; however, its radiation resistance will fall by a factor of four to R/4. So, if we apply a matched load to the new dipole of R/4, the power we can extract will be:
((V/4)^2)/(R/4) = V^2/4R

Exactly the same power as before! So the new dipole must have exactly the same capture area even though it's half the physical length! Even though it picks up half the voltage, this is compensated exactly by the drop in its internal source impedance.

In practice, of course, the lowering Radiation Resistance makes it increasingly difficult to extract the power efficiently; nevertheless, the odd fact is that capture area bears hardly any relationship to physical size when you are dealing with electrically short antennas.

Hope that helps some.
Steve G3TXQ

I agree if it works for you given your restrictions then its a good un. I have a friend who loves his StepIR. I do too but can't afford one hence I use bits of wire on HF.

There's a lot to be said for a simple lightweight dipole that you can erect high and in the clear; if you can rotate it, even better. Capacity end loading is also the best way of reducing the size without reducing efficiency too much. If I didn't have my Hexbeam I'd certainly be tempted to try something like this for 20m thru 10m.

My only problems with this particular commercial version are:

1) The potential losses you get by feeding it with coax and an impedance transformer.
2) The nonsense of calling it a beam!

73,
Steve G3TXQ

i agree it is a bit of a cheek calling it a beam .(when it only the upturnned version of his vertical) but the thing works well for me . had some good reports so far .

...I guess you need the cash to pay the fine if the neighbour's wife complains to the police?

73

dave