2m Cubical Quad

[HUGH]

I made a 2m. 4-element quad from 10mm copper pipe (about 3/8") and it was quite successful but far too heavy, dangerous to life and limb in fact. The modelling was done in both EZWpro and MMANA-GAL both of which tallied with each other just for once. I then did the same using stranded copper wire of 4mm x-sectional area, construction to be using 5mm diameter glass-fibre spacers on a 23mm diameter boom, the dimensions and characteristics were very similar.

The wire version performs like a piece of wet string, varying the element spacings makes little difference to the SWR so I presume the software-modelled dimensions are not correct and should differ more from the copper pipe version. On searching the internet I spotted that Cubex are making similar antennas and have spoken to a UK amateur who uses one and swears by it.

Anyone have any experience of this otherwise I may have to replicate the copper quad with an aluminium rod one? It's a pity because the wire one weighs very little and the glass-fibre is very cheap.

[wd0ct]

I know nothing about modeling but the wire version should have longer wire lengths than the previous tubing.

The other modeling guys can probably help you out.

[N8YX]

Owing to the decrease in element diameter, the wire antenna's 'Q' will be higher (and as a result, the usable bandwidth narrower) than the copper tubing version.

Does your modeling program allow you to change the element diameter and/or Q value?

[WB2WIK]

I made a 2m. 4-element quad from 10mm copper pipe (about 3/8") and it was quite successful but far too heavy, dangerous to life and limb in fact. The modelling was done in both EZWpro and MMANA-GAL both of which tallied with each other just for once. I then did the same using stranded copper wire of 4mm x-sectional area, construction to be using 5mm diameter glass-fibre spacers on a 23mm diameter boom, the dimensions and characteristics were very similar.

The wire version performs like a piece of wet string, varying the element spacings makes little difference to the SWR so I presume the software-modelled dimensions are not correct and should differ more from the copper pipe version. On searching the internet I spotted that Cubex are making similar antennas and have spoken to a UK amateur who uses one and swears by it.

Anyone have any experience of this otherwise I may have to replicate the copper quad with an aluminium rod one? It's a pity because the wire one weighs very little and the glass-fibre is very cheap.

::How are you evaluating performance?

WB2WIK/6

[HUGH]

Owing to the decrease in element diameter, the wire antenna's 'Q' will be higher (and as a result, the usable bandwidth narrower) than the copper tubing version.
Does your modeling program allow you to change the element diameter and/or Q value?

EZW allows change of wire diameter and, yes, you're quite right, it's critical so the Q is much higher and bandwidth less although it's theroetically fine over most of 2m. "EZpro" is better as it allows plenty of segments in each element, it was a fine and unusual present.
I made the antenna with some tension in the wire, the taut construction looks good but the dimensions are then slightly less. I've just rewired it with greater attention to accuracy and, if it ever stops raining, I hope to try it again today at about 20ft elevation over (wet) grass.

::How are you evaluating performance?
WB2WIK/6

Very crudely by firstly "looking" at various beacons and secondly I have in the house, about 50 yards away, a chimney-mounted antenna which I connect to my R5000. If it hadn't been raining so much here this summer I think I could have done a proper field strength check. Our field is very waterlogged and I don't want to take the R5000 down there.

[HUGH]

Well, I tried it again with meticulous attention to dimensions and it's still not well. I might change the coax, the main run is in perfect order, checked by terminating and running other antennas but the 10ft or so on this antenna may just have had some water in it being semi-airspaced. It's not evident but worth pursuing that theory.

[HUGH]

Having completed a "new bathroom" project I fished out this 2m wire quad, covered in sawdust, and it occurred to me that the problem might be the diagonal spacers.
The thin fibre-glass rods available are carbon-filled, I couldn't get plain rods or tubes below 10mm diameter (3/8") at the time and the supplier does state that all their black fibre-glass products, be it rod, tube, industrial profiles or whatever, are NOT suitable for electrical insulation.
The actual resistance per unit length is high, not enough to stop mA leakage at mains potential but I wouldn't have thought a problem at RF. Being diagonals though, they do support the antenna wire at points which are not at low impedance.

I have had apparent problems using the popular 30ft fishing poles at VHF but not at HF. They do seem to contain black fibres.

The first objective will be to use bamboo spacers temporarily, the "head gardener" hasn't used all the bundle of bamboo I bought her so I'll acquire those before purchasing more fibre-glass.

Have any other home-construction enthusiasts had trouble with black fibreglass?

[N5RLR]

It could be worse. The carbon could ignite at appreciable power. [click]

If you treated the bamboo [with shellac or something more modern], it might do as a permanent solution.

[HUGH]

I had a little fire with 100W HF tracking across a switch and it would have burned down my wooden shack in no time but we don't normally go away and leave our transmitter on do we? Before setting an antenna on fire at about 100 feet up I should wait until firework night.

The bamboo will be varnished first, it does add a little assymetry to a construction as well. My 2m omnidirectional vertical is mounted on a stout bamboo pole which was originally used to deliver carpets on. This is after I found the fishing pole detuned the antenna plus being insufficiently robust, it's now in 3 pieces.

[KB2BLS]

Go to your nearest farm supply store, like Tractor Supply. They sell fiberglass "fence poles or flag poles that the farmers use to mark their fields with. These are all white, can be painted, and non conducting. I've been using them for years. Items made with them usually have to be disassembled rather than repaired. They make great spreaders.