A simple 40 metre Vertical Antenna

 

Vertical antennas are well suited to DX-ing.  They offer a low angle of radiation for transmit; which is where you want your signal to go. On the downside, they are may be susceptible to local noise.   

 

Verticals also work well equally in all directions. This is also a downside if you are looking for directivity.  However, as an all-rounder, you can’t go past a vertical as a good DX antenna for 40 metres.

 

Parts List


 10 metre long Squid Pole (for portable or even semi-permanent use at home)

Mounting stake

10 metres of antenna wire

Radial wire ~ 10m per radial

Liquid tape

Radial Plate

Coax – RG58 spec fine

SO239 panel mount

 

Wavelength is 300/7.1Mhz.

Divide by four for a quarter wavelength

 

The Radiating element

 

The vertical element will be about 10.5m long.  You’ll need to fine tune this once you finalise your installation and attach all the radial wires.

 

Use tape to lock the squid pole sections into place so they don’t collapse.  Attach the radiating wire to the squid pole with tape.  Leave the top 50-100cm loosely attached.  You may need to shorten to achieve resonance.

 

Radials

Each radial should be 10m long.  If you are unable to get 10m in every direction, cut the radials to a length that fits.

 

The following diagrams illustrate the best way to lay your radials.

 

 

You should aim to lay a minimum of eight radials.  Sixteen would be better.  General wisdom suggests 30 as being a balance between practicality and performance.  Dedicated campaigners will lay 60 radials.  Laying 60 radials suggests OCD, a commercial installation or a perfectionist at work!

 

Consider various options for attaching your radials.  You can look at commercial options (search google for “radial plates for vertical antennas”), or better yet, you can construct something in your workshop.

 

 

Source: Internet Butternut HF6V

 

 

A simple 1:1 Choke Balun

 

The simplest construction approach is to wind a length of coaxial cable into a coil, creating an inductor from the outer shield.

 

This method is cheap, simple and will suppress common mode currents.   For 7Mhz, wind about 6m of coax into a coil about 6-8 turns.  Use some electrical tape to secure the coil in two or three places.

 

If you need 15m of coax to run from your shack to the antenna, then add about 6m to allow for winding the chock balun.  Attach PL259 connectors at each end.

 

 

Construction and Tuning.

 

Once you have decided on how you want to attach your radials, run them out and ensure they are either buried or secured to minimise trip hazards and/or mishaps with the lawn mower!

 

These diagrams (courtesy: Hustler Antenna Manual) illustrate the “dos and don’ts” for laying your radials.

 

 

 

 

 

Erect the vertical and solder the radiating wire to the SO239 mount.   Solder the radial common line to the mount.

 

If your installation is permanent, consider digging a shallow trench to run the coax from the shack to the base of your vertical.  Run the coax through some conduit or similar, under the radials.

 

Attach the coax (run the coax under the radial wires) back to the shack and check for resonance.

 

Depending on what tools and meters you have in your shack will determine how you go about fine tuning your vertical.

 

As we (hopefully) made the vertical radiating wire too long to begin with, you’ll almost certainly need to shorten it.  Do this carefully.  It’s far easier to keep trimming a little at a time than to add wire if you cut back too much.

 

You should be able to get the SWR under 1.5:1 and expect a reasonable band width.

 

Commercial Alternatives

 

There are various commercial suppliers of vertical antennas.  Do some research.  Read online reviews and speak to other operators or friends at your local club.

 

Some examples include:

 

  • Hustler BTV series
  • Hy-Gain 
  • TET Emtron (VK)
  • Cushcraft
  • GAP
  • Steppir