Author Topic: Spherical spiral antennas for HF?  (Read 2136 times)

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Offline rhbTopic starter

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Spherical spiral antennas for HF?
« on: September 16, 2018, 07:46:31 pm »
Does anyone know of work on building a broadband HF antenna based on the spiral on the surface of a sphere design?   Both Balanis, 2016, and Stutzman & Theile, 2012, show spiral examples.

 It looks as if with a program to account for catenary and stretch it would be a reasonable tree supported insulated wire antenna.  Not as simple as a trap dipole, but not too much more complex other than threading all the wires through the support strings with enough strings  to adequately approximate a sphere.
 
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Offline hagster

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Re: Spherical spiral antennas for HF?
« Reply #1 on: September 17, 2018, 07:32:16 pm »
I have never seen one. Looks like you could be the first.
 

Online 2N3055

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Re: Spherical spiral antennas for HF?
« Reply #2 on: September 18, 2018, 06:41:49 am »
Look for term "loxodromic antenna"..
 

Offline hagster

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Re: Spherical spiral antennas for HF?
« Reply #3 on: September 18, 2018, 07:31:50 am »
To qualify my statement. I have never seen one at HF.

This is s similar,but conical version.

https://www.tcibr.com/product/tci-model-570-multimode-spiral-antenna/
 

Offline rhbTopic starter

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Re: Spherical spiral antennas for HF?
« Reply #4 on: September 18, 2018, 02:26:49 pm »
Thanks.  They sell some very interesting antennas.  I rather fear they are "no such agency" priced as you must send them your info to get a datasheet :-(

But they have multiple models which cover 2-30 MHz which is precisely what I'm after.

A cone has more gain along the axis of the cone, but I think it is related to the aspect ratio. So a short cone or pyramid should be very similar to a hemisphere and much easier to construct.
 

Offline hagster

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Re: Spherical spiral antennas for HF?
« Reply #5 on: September 18, 2018, 06:55:15 pm »
Well at 2MHz it would be about 50m in diameter and 25m tall. That would never be cheap.

20MHz and up is probably in the range of a DIY setup.

I havent modelled it, but I guess peak gain would be straight up. So good for skywave stuff.
 

Offline rhbTopic starter

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Re: Spherical spiral antennas for HF?
« Reply #6 on: September 18, 2018, 08:55:30 pm »
I was able to get the data sheets for some.  The 545 spiral pyramid is 40 ft tall and 85 ft on a side.  However these all run in the $50-100K range.  The circular spiral is around 340 ft in diameter.

Generally they all have a VSWR of 2:1 or less from 2-30 MHz.  An interesting aspect is that several models support multiple modes, so as many as 3 transmitters can share a single antenna.  They have pretty good low angle radiation in a couple of modes.
 

Offline cdev

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Re: Spherical spiral antennas for HF?
« Reply #7 on: September 21, 2018, 12:36:16 pm »
You might do better with a "43 foot vertical". And much cheaper, especially if you are owned by a tree.
"What the large print giveth, the small print taketh away."
 


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