Raised aerial 7ft and in the clear

On the plus side, your reception of banking aircraft has gone right up!

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From the video above it looks like there is quite a lot of flex in that top pole section. Is it plastic? That whipping action will be creating quite high loads on the bottom joint.

What do you have in the box at the top? If possible, putting it lower down would be a advantage - it would reduce the mass and windage at the top and as a result the turning moment on the bottom joint. Also using a stiffer pole would help as it would reduce dynamic loading. I’m using a thin walled steel tube which doesn’t noticeably flex in the wind and is still quite light.

That centre stub is solid up to the first box which is the balun for the 6m through to 20m elements, then the top part is a fibreglass extension for the 40m element and the box at the top is the balun which doesn’t have much mass.

I’m right on the limit, the manufacturer claims it’s good to 75MPH and allegedly the highest winds recorded in Essex were just down the road here gusting up to 78MPH.

It’s moved overnight and here’s how the centre base section looks now.

base

It’s definitely being held in place by the three coax runs and it does look as though it’s lifted up out of the centre.

Here it is on the ground prior to erection.

prior

So it’s kept in centre base just by the three coax runs with no additional screw to secure it?

The design changes but I think this is similar to the one I have. There’s a big chunky grub screw holding the yellow collar in place. Either the grub screw has worked loose or the post worked its way out.

Without getting it down, it’s impossible to tell which.

base

My Jetvision antenna sits on top of a long pvc pole so the polarisation is almost never really 100% vertical :smiley:

Could you put a cord between the top of the metal pole across to the PVC pole to draw it in and upright?

If you look closely you’ll see that there’s already an aluminium rod connecting the metal pole to the PVC pole to reduce the swinging. Unfortunately I have no other anchoring points available to stabilise it even more because the pole is longer and further away than it looks in the picture.

Oh yes, I see it now, it’s already quite high up. It’s hard to judge the angle; the antenna looks like it’s around 20 to 30 degrees from the vertical? That would mean around a 6% to 13% reduction in signal strength compared to what would be received vertically (based on cosine of the angle from vertical). So it probably means a small loss for the weakest vertical signals far away but otherwise no real issue. And possibly offset by weak aircraft turning at the same angle far away.

My stats are well down today compared to others nearby - Hardly surprising considering the aerial is almost horizontal.

Ouch - not so good. Would have been good to have a deeper mounting socket at the top for the pipe to drop in to. Must have been heartbreaking watching the wind taking hold of the antenna.

Don’t forget that the weakest signals over about 250nmi will already have a polarisation ‘pre-skew’ of a couple of degrees due to the curvature of the earth :wink:

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When you get it down, might want to consider a pin through it instead of just the grub. Or if you dont want to drill the casting, rig a worm clamp with a safety leash thing to stop it from moving upwards in case it happens again.

Don’t worry, Keith is considered a leading authority on metal pins nowadays :wink:

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Heh, good point, that comes out as just over 4 degrees, but that is only a signal strength loss of a bit less than 0.3% from vertical at the same distance.

The aerial manufacturer has come back to me and said that he’s actually redesigned the post setup since then and that he’s confident this can be fixed assuming no more damage is done in the mean time.

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The back spreader has snapped, the whole aerial is laying horizontal now and looking very sorry for itself.

IMG_2128

IMG_2132

The performance isn’t quite as bad as I’d expect but it’s well down on normal.

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Many would be happy having such a performance…

Still, a sorry sight :confused: Can it be easily repaired, once it is lowered?

@keithma
Sorry to hear about sad incidents.
First your arm/shoulder broke.
Now your antenna broke.
:sob: :cry: