144 MHz 2m dipole for SOTA

Simple 144 MHz 2 metre dipole for mounting on a telescopic fishing pole or as we call them in Australia a ‘squid pole’.

This antenna comes to you from the homebrew shack of Andrew VK1AD.  No this antenna doesn’t have a brand name, doesn’t claim to be a miracle device and isn’t supplied with a 1 year or a 2 year extended warranty.

Yes it’s a simple 144 MHz half wave dipole antenna using 3 mm copper wire and a couple of adapters.   Some of you may have similar adapters in your junk box.  What does it cost?  You will be surprised to know it’s not $$$$ hundreds, not even $20.00 The adapters are a few dollars each purchased from an eBbay supplier and the wire was salvaged from a former telephone line.  The black plastic cable tie is from a bag of 50 purchased from a nearby hardware store at $4.00 per bag.  For the homebrew champion you can construct this antenna yourself.  Fear not, if you don’t have the exact adapters you can improvise,  think of different way to support two pieces of wire only 497 mm long (19.5 inches).  My inspiration for homebrewing this antenna was a joint SOTA activation with Al VK1RX and an expedition to Mt Kosciuszko with Andrew VK1DA   *I will take this opportunity to acknowledge Al’s 2m dipole design as the basis for my homebrew attempt, the difference is the center support. I will take a guess and assume Al’s design uses wire elements of a similar length. ;)

P.S.  I forgot to mention you can store the 1/4 wave copper wire elements inside the squid pole, rather than bending the elements to fit in your backpack.

Below are pictures of the antenna components, go for it, enjoy making your own 144 MHz 2m dipole for your next 2m SOTA activation.   Simplicity is the key to a successful SOTA activation. :)

Photos: © Copyright 2013 – 2017 Andrew VK1AD

Parts:

  • 1 Banana binding posts to female BNC adapter
  • 1 male BNC to SO239.  Not required where your coax is fitted with BNCs.
  • 1 Black plastic cable tie
  • 2 lengths of 3 mm solid copper wire 497 mm or 19.5 inches.  What ever you have on hand.

Fig 1:

2 metre dipole components: 2 lengths of 1.6 mm enamel copper wire, a BNC to Banana adapter and a BNC to SO239 adapter

2 metre dipole components: 2 lengths of 3 mm enamel copper wire, BNC to Banana adapter, BNC to SO239 adapter and 1 cable tie.

Fig 2:

small loop at the end of each dipole element

small loop at the end of each dipole element

Fig 3:

Loops at the far end of each element to prevent eye injury when assembling the antenna

Loops at the far end of each element may prevent eye injury when assembling the antenna

Fig 4:

Banana adapter and cable tie. The cable tie passes over the squid pole

Banana adapter and cable tie. The cable tie passes over the squid pole

Fig 5:

Banana and BNC to SO239

Banana and BNC to SO239 adapter or you may prefer to use a BNC to N adapter

The VSWR at the 3rd harmonic frequency 432 MHz is below 1.2:1 making the antenna usable on 70cm.  If you prefer to make a 70cm version (432 MHz), cut two additional wires each 165 mm, excluding the short section in the binding post. 170 mm will be a good start point. Measure 5 mm along the wire and make a right angle bend. Next secure each 1/4 wave element in the binding post. You now have a 70cm 1/2 wave dipole which you can confidently use for a SOTA activation.

A different option is to mount two dipole antennas on the same pole, one each for 2m and 70cm and feed the antennas with a VHF/UHF duplexer. Vertical separation can be achieved by positioning the 70cm dipole above the 2m dipole. Adjustable cable ties will help to position each center connector on the pole.

For operation on 70cm my advice is to use low loss 50 ohm coax fitted with N connectors.

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Last Update: 28 April 2016