2m Yagi Modification – 20 April 2013

2m/70cm Arrow 3 element Yagi – upgade to 5 elements

I purchased a 2m/70cm Arrow Yagi about 3 years ago for Satellite work. The antenna has 3el on 2m and 7el on 70cm with a 10 watt duplexer and BNC connections. I have worked many VK contacts up and down the east coast of Australia on SO an AO birds. The arrow has been gathering dust for about 12 months, so it was about time it saw some action on the mountains, no not for satellite work, yes for 2m SOTA activation via Aircraft Enhancement (AE).

The Arrow first featured on Mt Gingera 9 March 2103 mounted on a camera tripod about 1.5 metres above the surface of the summit. On that occasion I used the Arrow to make 5 VHF contacts of which 2 were genuine DX with the best contact to VK2ZT Steve in Port Stephens 421 km. (see Mt Gingera post)

The second outing for the Arrow was on 10 March 2013, on the summit of Mt Tennent (see picture below) on that occasion I worked 3 VHF DX contacts. (see Mt Tennent post) The antenna is mounted at the rear of the reflector which means the weight is not centred over the camera tripod. In the picture below you can see what looks like to be a handle on the rear of the yagi. The extension was made to balance the weight and enable rotation of the boom. This needs to be fixed.

Having 3 elements on 2m the antenna needed a little more oomph (technical term for gain) so I decided to extend the boom and add 2 more directors. I also wanted to mount the antenna on the on the squid pole about 3 metres up. This would enable quick rotation when dealing with different chaser locations.

2m 3el Arrow Yagi

2m 3el Arrow Yagi on Mt Tennent

On Saturday 20 April I took a break from SOTA activations to wrest my ankle, work on the portable yagi and do a spot of SOTA chasing. My last attempt at aircraft enhancement (AE) with VK3HRA Allen, whilst successful, involved a `heavy’ activation using a 4 element beam, a 3.5 metre painter’s pole and other bits and pieces.

That was fine given the location was Mt Ginini, where one can park the car below the activation zone and human pack-horse the gear up the hill.

The next attempt at AE will be next Sunday morning 28 April from Mt Ginger Ale VK1/AC-007 (see Mt Ginger Ale post). I will be attempting a VHF S2S with a like-minded VK3. Anyway this activation involves a 12 km walk to the summit of Ginger Ale, therefore I need a yagi that is both portable in construction and lightweight.

The design I have chosen is DL6WU 5 element using Yagi Design software by VK5DJ John.

Between chasing VK5PAS Paul, and VK1RX Al, the 3el Arrow is now 5el and supported by the squid pole. The antenna boom breaks into 3 sections and the elements fit in a small narrow bag. Rather than clamping the antenna to the squid pole with a pipe clamp and damaging the fibreglass tube, I have used a short section of plastic pipe as a sleeve which rests on the top of a section of the pole.

Here are 4 photos of the modified yagi.

Sleeve mount over the squid pole

Sleeve mount over the squid pole

Modified boom and additional elements

Modified Antenna

Additional Elements (4 mm aluminium rod)

Additional elements (4 mm aluminium rod) and boom extension

Elevated on the Squid Pole

Elevated on the Squid Pole. Looking good!

So how does it perform? On Sunday 21 April at 0800 local I joined the VHF DX net on 144.200 MHz. The aim is to contact a VK2 or VK3 via aircraft enhancement. The VHF DX net operates every Sunday morning and its not unusual to work stations 400 to 500 km away via aircraft enhancement. Canberra is directly below the flight path of commercial aircraft flying at 35,000 to 40,000 ft between Melbourne and Sydney, plus A380s and 747s from the pacific routes fly into controlled airspace just south of Canberra. The yagi was mounted on the squid pole as shown in the picture below on the rear deck of the house about 5 metres above the ground. The mounting would be the same in the field.

At 0900 local I heard VK3II Jim at Corent Bay call CQ from QF21rn 470 km south west of my location at QF44mp. Jim’s signal was 5-6 and getting stronger, I replied, Jim was very surprised to hear me with a 5-6 report. The conversation lasted for about 4 minutes before losing contact. During the contact I was monitoring FlightRadar24 on my iPad, it was showing an A380 in the transmission path. The FT857D was running on external batteries, two 9AH SLA feeding 45 watts into the yagi. A great result, very happy with the modification. Looking forward to using the yagi on Mt Ginger Ale next Sunday 28 April 2013.

Working Jim VK3II from the back deck.

5el Yagi pointing south west towards VK3II mounted on the squid pole.

Same antenna now with the 70 cm elements added.

2m and 70 cm yagi.  5 elements on 2m and 7 elements on 70 cm.

2m and 70 cm yagi. 5 elements on 2m and 7 elements on 70 cm.