Online Amateur Radio Community Wiki

This page is read only. You can view the source, but not change it. Ask your administrator if you think this is wrong.
[[oarc-sota-day|Back to the main page]] | [[oarc-sota-day-beginners|Back to What Should I Take 
]]

====== Antenna Ideas ======

The primary goal for any SOTA antenna is to be lightweight while also being somewhat efficient. Typically setups use low power (unless you have strong arms!) so we want to get the best out of them.

We have to also consider the support structure for the antennas as well as the antennas themselves. Fiberglass poles are popular as they won’t detune any attached antennas. They are also lightweight and can usually stow to a short size, which is useful for carrying in a rucksack.

To-do: add info and links.
===== HF Antennas =====

Wire antennas tend to be the most popular antennas for HF SOTA activities due to their multi-band and lightweight properties. Beams aren’t too popular due to their complexity, but that doesn’t mean people don’t try! Typically  wire antennas are fed from one end of the wire, resulting in a high impedance. Thus a transformer is used to bring the impedance down to the required 50 Ohms.

Wire antennas also require very minimal support structures. One or two poles can be used, and you may get away with not requiring guy wires as well in some situations.

Here’s some DIY plans for some wire antennas that are used a lot for SOTA.

  * [[https://m0ukd.com/homebrew/baluns-and-ununs/91-magnetic-longwire-balun-unun/|M0UKD Random wire antenna]] using a 9:1 transformer
  * [[https://elginradio.wordpress.com/2017/10/17/end-fed-half-wave-antennas/|End-fed half-wave antenna]] using a 49:1 transformer (versions for 64:1 transformers also exist)

You can, of course, buy these pre-made or in kit form from various retailers as well.
===== VHF/UHF Antennas =====

==== Beam Antennas ====

At this wavelength beam antennas become small enough to bring up hills. Yagi antennas for 2m are not uncommon, and the Moxon is an excellent design, but for the vast majority of people a vertical antenna may be fine.

  * Links to Yagi plans
  * Links to Moxon plans
    * http://www.antentop.org/w4rnl.001/mvhf.html
    * https://reflector.sota.org.uk/t/home-brew-2m-moxon-fairly-lightweight/13123

==== Vertical Antennas ====

Popular vertical antennas include coax dipole types, 1/4 ground plane antennas with some radials, or j-pole/Slim Jims made from ladder line. A mast of some kind is useful to get them up high for better line of sight to the horizon.

=== Slim Jim ===

A Slim Jim is a small, robust, roll up antenna that can be bought ready-made or [[https://m0ukd.com/calculators/slim-jim-and-j-pole-calculator/|easily home made]] from ladder line, a length of coax and a connector for your radio. The default velocity factor on the calculator page is for bare copper which is too high for insulated ladder line - 0.8 to 0.89 is a closer estimate. The feed point can be weak so either make sure it is aligned with the centre support material or don't strip the insulation completely. Combined with an collapsible pole that can be strapped to a fencepost or supported on a ground spike makes for an effective - though single-band - antenna setup.

  * Links to vertical antenna plans

==== Dipole Antennas ====

Dipole antennas of various types are also popular for portable VHF/UHF expeditions, and some people use them to good effect on SOTA trips. Coax dipoles are included here, but some people would probably put them as a vertical. We’ll leave that debate and whether all vertical antennas are actually dipoles for an antenna theory class, though. 

  * https://vk1nam.wordpress.com/2019/07/21/sota-lightweight-portable-2m-70cm-dipole-antenna-update/ - a lightweight dual-band dipole with integrated toroidal choke
  * https://vk2zoi.com/articles/dual-band-half-wave-flower-pot/ - excellent design, easy to make and both Simon-M0SMU and Vic-EI7IYB have made versions.


===== Masts and supports =====

Here’s some recommendations for masts and supports.

  * [[https://www.sotabeams.co.uk/|SOTABeams]] do extensive poles and guying systems.