Multi Band Slinky Doublet

Designing an HF antenna for Swindon Makerspace presented several challenges:-

  1. Routing coax from Makerspace to the roof is potentially tricky
  2. High external vertical antennas would require lightning protection
  3. No convenient external earths available
  4. Counterpoises impractical due to size
  5. Large horizontal antennas (long wire, dipole) would probably not be appreciated by the property owners.

Initial WSPR Results

These issues ruled out my ‘go-to’ antennas; fan dipoles and verticals.  Not sure how to proceed, I visited the Makerspace armed with an FT817, a short loaded 40m vertical, some random lengths of wire and an LDG auto ATU.

Running WSPR (~2W) resulted in many spots on several bands all around Europe. This gave me hope 🙂

The Makerspace is approximately 10 metre square, with a sloping roof.  I considered folded dipoles and loops but both have their limitations (single band antenna or very high Q).  A doublet seemed a potential solution but the highest path in the roof space is only 10m long, too short for anything below 20m (14MHz).

The Raw Ingredients


I’d previously read several articles (eHam, RadCom) regarding the use of Slinkys as antennas. Further research showed a single slinky can stretch to ~5m in length and contains ~20m of coiled wire. To make this a multiband antenna I figured I could feed with twin-feed (aka ladder line) connected to a balanced ATU.


The Finished Slinky Antenna


Say hello to the Makerspace Slinkyantenna!

Supported with nylon rope and with slinky’s extended to almost touch the walls.  It’s a compromise on several levels but initial tests (FT817, LDG ATU, DIY balun) suggest it’s usable on most bands >= 40m (7MHz).  Initial frustrations when Gergana LZ1ZYL (Bulgaria) couldn’t hear us were later explained when the other stations calling mentioned the power they were using.  When our ~2W QRP signal was finally heard, an S8 report was received and details exchanged without issue (she was S9+10, running significantly more power).

Test Station Showing First Contact QRZ


We plan to kit out the space with a balanced manual ATU and a 100W transceiver.  The station will be available for use by licensed members on a 24×7 basis.

Our long term aim is to recruit other full license holders and ultimately request a dedicated Swindon MakerSpace club callsign.

Interested in joining the Makerspace?  Have a solid state HF radio you may be willing to part with? Please get in touch :o)


 What is Swindon Makerspace?


Makerspace Wall Logo

Swindon Makerspace; a not-for-profit registered C.I.C. (Community Interest Company). We like to break and make things.  Many different things – robots, aircraft, computers, electronics – anything goes.

For more information see Swindon Makerspace.

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