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Electronics => RF, Microwave, Ham Radio => Topic started by: rhb on September 16, 2018, 07:46:31 pm

Title: Spherical spiral antennas for HF?
Post by: rhb 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.

Title: Re: Spherical spiral antennas for HF?
Post by: hagster on September 17, 2018, 07:32:16 pm

I have never seen one. Looks like you could be the first.

Title: Re: Spherical spiral antennas for HF?
Post by: 2N3055 on September 18, 2018, 06:41:49 am

Look for term "loxodromic antenna"..

Title: Re: Spherical spiral antennas for HF?
Post by: hagster 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/ (https://www.tcibr.com/product/tci-model-570-multimode-spiral-antenna/)

Title: Re: Spherical spiral antennas for HF?
Post by: rhb 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.

Title: Re: Spherical spiral antennas for HF?
Post by: hagster 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.

Title: Re: Spherical spiral antennas for HF?
Post by: rhb 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.

Title: Re: Spherical spiral antennas for HF?
Post by: cdev 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.