Homebrew Portable HF Antenna

 As I am restricted to loft aerials at home (a modern house with restrictive covenants preventing  external antennae), I decided to put together a portable vertical antenna which I can either use /P or temporarily erect in the garden and take down when not in use.  Ideally, it would be low cost, and also allow me to operate on some of the bands not covered by my fan dipole in the loft space.

The mounting arrangement I went for consists of an old wing mirror mount fitted to a section of old tent pole as an earth spike.  On top of the mirror mount is the top section of an old discone antenna that I had previously drilled out to take an SO-239 barrel with the intension of using it as a ground plane kit for mobile antennae.  I never throw anything out so it came in handy as an easy way to connect counterpoise wires.  I initially used 3 counterpoise wires, cut to roughly 1/4 wave on 12m, 15m and 20m.

The top section of the antenna was based around an adjustable inductor and a 5m telescopic whip.  The inductor is homebrew using a coil former that Nigel G4ZAL kindly 3D printed for me.  The coil is wound using stainless steel wire and adjusted by sliding a Jubilee Clip up or down the coil.  The Jubilee Clip is shorted to the base of the coil using a short wire.

You can see the finished antenna in the included images.  As I only used 3 counterpoise wires, I used some of the aluminium rods from the doner discone antenna as additional counterpoise.  They contribute little at HF but as I had them, I thought "why not?".

Initial impression was that the antenna was easy to tune between 30m and 40m using the fully extended telescopic whip and adjusting the inductor for lowest VSWR.  For 20m and above, the coil was shorted completely (by moving the Jubilee Clip to the top of the coil), and the length of the telescopic section adjusted for lowest VSWR.

  

Having spent a little time on FT8, screen shots from PSK Reporter for 20m & 30m are shown above.  Seems to be working well, despite my valley floor location at home.  I am now looking forward to further testing and to taking the new antenna up on to high ground to see how it performs.