Why A Linked Dipole ?
What are the advantages to this type on antenna?
- Easy to change bands
- Easy to repair and maintain – including in the field
- Full sized dipole antenna on each band
- Antenna provides two of the guys for your mast – just need a back guy
- Radiation point of antenna as high as possible for best performance
- No lossy matching networks – your power gets radiated, not lost!
- Packs up easily – no parts to lose.
- Excellent for QRP operation
What parts will I need?
1. The antenna build is based on the Linked Dipole Hardware Kit from Sotabeams, if you want
to make a four band antenna then you will need 2 extra links .
http://www.sotabeams.co.uk/linked-dipole-hardware-kit/ the kit is currently £5.99 plus p & p
2. Antenna wire – work out the lengths you need at half-wave and add them up – don’t cut any
wire until you check out our cutting guild. you can also get this ire from Sotabeams, or any other wire supplier.
A 7m fishing pole, shop around for these I seen them from £6 to £23, the last one I got was a
few quip because the last to end sections inc the one with the fishing loop on had been lost.
3. Antenna Coax – RG58 will fit – do not do as I did try to drill out the holes in the plastic to
try and use mini 8 – it just broke the plastic.
4. Connection plug PL-259
5. Small length of lightweight shock cord – a 2 metres will do it.
6. Guy rope material.
7. Three or more tent pegs.
Winders to store your antenna on.
See : http://www.sotabeams.co.uk/wire-winders/ these should not break the bank at £2.50
also from Sotabeams.
You will need to seal around the center T-peice a glue gun will do for that.
Or you could splash out and buy some liquid electrical tape (also from Sotabeams)
20m 4.78 + 5cm x 2 for clips + 5 cm tail
30m 1.84 + 5cm x 2 for clips
40m 2.71 + 5 cm x 2 for clips
80m 8.24 + 5 cm x 2 for clips
All with + 5 cm except 80m
22AWG wire – around £3 for 100 mtrs
Use 300/F (Meters) or 234/F (Feet) to get the measurements for your inverted V wavelength, remember you want a 1/2 wavelength divided in two for each leg making 2x 1/4 wavelength legs. Alternatively use a app or spreadsheet calculator as can be easily found online.
1 wavelength (Meters) = 300 / frequency in MHz = two dipoles
1/4 wavelength (Feet) = 234 / frequency in MHz = each dipole side
Denis’ 3 cut antenna Maths….
amount to cut off = ( (frequency measured on analyser/frequency desired) * actual measured length ) – actual measured length
we measured resonance by observing lowest SWR at 3,300KHz. We required resonance at 3,650KHz.
3300/3650 = 0.904
this could lead you to think that your antennas wire length should be 90.4% of the length it is. So multiply the actual length by 0.904
take this value and use around 80% of it and cut off that amount from both sides of the dipole antenna.
Recheck using the above formula. You should notice that you are around 80% of the way to where you want to be. Observe if there is any difference as this will effect your next cut.
E & O.E
Authors Paul Archer M0PJA and Denis Soames M0USV.
Thanks to Richard at Sotabeams for his help.