The 80m "portable" phased vertical array!

M0LMK

Member #2
Full Member
Staff member
Once a year, I organise a mini dxpedition to a lovely farm in North Devon where we have access to a huge field and a few comfortable holiday cottages. The noise floor is very low and it's about 1 mile from the coast so it's a great spot for radio. The owner is great and we put up all sorts of silly antennas for a week of experimentation, operation and general fun. I usually take between 6 and 9 club members who want to spend a week immersed in our hobby and we use the club callsign, GX0HRS.

Last time we visited in 2019 (we missed 2020 for obvious reasons!) with a crew of 5, our antenna farm consisted of a DX Commander vertical, an 80m EFHW configured as an inverted L, a ZS6BKW and a 160m dipole hung at 10m height. They all worked well but didn't offer much in the way of performance for the low bands so this year we've upped our game and will be taking a 3 element tri band beam for 20, 15 and 10m together with a 12m pump up SCAM mast which sorts out the high HF bands but I wanted something a little special for the lower bands...

In comes the 2 vertical phased array. A fairly simple concept of taking 2 matched verticals and feeding them out of phase to create gain along with a nice F/B ratio. I won't go into details here as there plenty of resources online that do it much better than I can! The aim of this thread is to document the build process, costs and ultimately, the performance of a large vertical array for semi portable use.

So lets begin...

First up is the masts. I managed to purchase 2 very substantial 18m 100% fiberglass poles from china. They took 4 weeks to manufacture and another 3 to ship. The total cost for 2 masts including the shipping was around £300. Organising and importing was an absolute pain so I would advice against it for the sake of saving £50 and suggest you look at the 18m "Nebula" masts from DX Commander which are pretty much the same spec.

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They are 1.71m tall when collapsed and the biggest tube is 72mm in diameter. Quite heavy and very sturdy with the lower sections having 3mm thick walls and the upper sections decreasing in thickness to help reduce the weight. I need to come up with a way to stand them vertical and guy them...
 

M0LMK

Member #2
Full Member
Staff member
While waiting for the masts, I built the relay box and controller that allows the operator to select which direction the array "shoots" in. It's a straight forward build and the excellent videos by Colin, MM0OPX on YouTube made it very easy to follow along.

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If the verticals were mounted in the West and East, the phasing box allows the signal to be pushed to the East, to the West or to the North and South at the same time. Total cost for the phasing system with 30m of control line (excluding phasing coax) was around £35

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The outside relay box is shown above on the left. The feeder from the radio and switch control cable (30 meters of 3 core 0.75mm cable) enters on the back. The in shack switch box shown above on the right. The LED on the switch box show which way the array is firing and allows the operator to easily switch the array direction.

Total cost so far: £345
 
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M0LMK

Member #2
Full Member
Staff member
Radials are next on the shopping list. Each vertical needs it's own radial system to work against. I was originally going to go with 16 x 20 meter long radial per vertical but after doing some research, I decided upon 32 x 10 meter long radials per vertical. I ordered 700 meters of 0.75mm tri-rated cable (I only needed 640m but will use the extra for the radiating element) at a total cost of £106.

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I made up 16 bunches of 4, 10 meter long lengths of the tri-rated cable and attached a 6 mm ring terminal to the end. It's crimped, soldered, hot glued and then has a glue lined heat shrink applied. The ends of the radials have been dipped in liquid tape to help prevent water ingress.

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I needed some way of connecting the radials so I turned to the DX Commander (Callum, M0MCX) who was kind enough to supply me with 2 of his water jet cut aluminium radial plates for his massive Nebula antenna.

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The plates were supplied unfinished so I bent up the tab for the SO239 connector, tapped 8 of the holes with an M6 tap and fitted some 6mm stainless bolts, washers and wing nuts.

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That should make a nice and tidy radial system with 32 radials per vertical.

Total cost so far: £451
 
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