Antenna of the Month.  Nov 2002

Details supplied each month by George, G3NIR

Antenna of the month.

The DOUBLET

This antenna will perform well on most bands if designed for the 20 metre band, with the exception of 160 metres. It is two half waves in phase on 20m, a half wave dipole on 40m and a quarter wave dipole on 80m. You will get good results on the higher bands as well.

The Doublet consists of two half waves in phase giving about 1.98dB of gain. About 1.5 times erp

So for your 10 watts it is effectively 15 watts radiated power on 20m only.

Parts list: 70 feet of either copper or pvc stranded wire

                 2 egg insulators

                  1 dipole centre (preferably ribbon feeder type)

                  Length of 300ohm ribbon feeder to suit length back to ATU.

Cut the wire in half to give two lengths of 35 feet each. Fit egg insulator on on end of each, measure a length of 33ft 6 inches and secure to dipole centre, leaving a tail coming from each dipole length. Join your length of 300ohm ribbon to the two tails at the dipole centre and thoroughly waterproof this joint, if possible fit into a small plastic film canister and fill with epoxy resin or some other type of solid adhesive. It is important that the point of join with the ribbon feeder and the dipole centre is very secure so that swaying in the wind will not lead to the ribbon cracking or breaking at that point.

Take the other end of the ribbon feeder and fit to the ATU preferably a balanced ATU such as a

Hoist the antenna into the air as high as possible, though I have used it as low as 18 feet with success.

It can be used as an inverted vee but this will affect the radiation pattern . In that you will not have a nice figure of eight broadside on to the antenna.

 With thanks to "Practical wire antennas" by John D Heys G3BDQ .  

  Click for other issues of Antenna of the Month.   Nov Dec  Feb Mar