TopBand: Slinky Beverage

Thu, 31 Jul 1997 14:50:36 +0000

> From:          W2pm@aol.com
> Date:          Thu, 31 Jul 97 13:07:07 +0000

 Hi Pete,

> Does anyone have any experience with a slinky beverage?

I played around with slow wave structures (which is what that would 
be) in the 70's.

> This antenna should behave like a 1 wavelength long end-fed wire and when
> terminated should provide the expected directivity. Any opposing views to
> this?

Coiling the wire does several things. One thing is it increases the 
phase delay along the wire, another is it increases the 
surge impedance of the wire. There are other effects also, but those 
are the main issues.

500 feet of wire in a ten foot area does NOT work like 500 feet of 
wire stretched out. The Beverages directivity is determined by 
the spatial area it occupies as well as the phase delay along the 
wire.

The ideal phase delay depends on the spatial (or physical) length of 
the antenna, as well as the rate of propagation along the wire. For 
a half wave long physical area, optimum Vp is about .5 freespace.

Kraus covers this in his book Antennas, as does "Kuecken" on page 72 
in Antennas and Transmission Lines (published in paperback by MFJ as 
book number 3305). The Kuecken book has an entire section on 
travelling wave antenna theory, and Kuecken is rated in the top 1% 
of inventors based on patents held.

I'm sure, from my experiments in the 70's and theory, the 
impedance of a "slinky Beverage" is much higher than the same six 
non-coiled conductor. I'm also sure the optimum Vp varies with the 
overall length of the structure. 

You'll probably just have to build one and see if it makes you happy 
or not, with the understanding that it probably will never be as good 
as a conventional Beverage unless you stumble on a good combo.

You could model it on a NEC based program, buy using a large number 
of inductive loads along a thick wire. You can watch the pattern and 
impedance change as you change the inductance. 

73, Tom W8JI 

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