Imax 2000, to reinforce or not to reinforce?

I bought a second hand imax 2000 and got a message from the seller that the top was broken just above the joint, so he let me have it for free . Asking around on the dutch CB facebook group for a top section i got a lot of offers for imax antennas with the bottom section broken. This leads me to the question: Should i reinforce the joints (i've done some rodbuilding, so know a few things about fiberglass and epoxy) or would this disturb the balance of strength between top and bottom section? Anyone any advice?

Nice one Karel.  

Nothing like getting something for free, especially if you can attempt a repair.

I believe a few members here have the Imax 2000 so hopefully they may be able to give you a better insight.

First thoughts to broken bottom sections is that they may have firmly attached the base section to a wall or some such and oscillations further up in winds would've caused harmonic stress damage at the fixed points. (?) These type of antennas generally survive better when also mounted on a pole, the bottom pole allowing the whole antenna to sway and taking the stresses away from the fibreglass sections.

Well, that's my tuppence thoughts to it anyway.

I hope you get it sorted, from what I've heard they are great antennas.


All the best,
Victor

Used one for years portable at 290m asl with the wind straight off the Somerset levels and not once did I ever think the joints needed strengthening , did have a phone clip once with the bottom section bent like a bannana , as Victor said failures are most likely due to incorrect installations. Dont panic about the top section doing a dance in the wind either as that takes the strain off the two lower sections ( willow and oak thing ) Only thing I ever did with mine was to redrill and fit better clamps as one snapped one freezing cold November morning (2014) whilst setting up portable.

Tonight i got the second(much older) antenna. Now i've got an itchy feeling on my hands caused by fiberglass splinters. From this on i'll take the top and give it a layer of epoxy varnish. Then give all the three sections a nice new white spraypaint job. Mounting it on the telescopic mast, of which the top section is an old surfpole should be just what the doctor ordered concerning evenly distibuting the stress.

No need to reinforce anything. Mine is over 20 years old and managed to cope with this year's winter storms just fine sat 10 metres in the air.

And it's up! Took an swr measurement with my nanoVNA from 26Mhz to 29Mhz, nowhere higher then 1.6! The lowest at about 28Mhz, 1.13!

Follow your instincts - in anything constructed or installed or both, no harm came from a bit of precautionary making it a bit more stress and weather resistant. Remember, antennas endure a lot of varying conditions changes and inherently suffer from passive and active galvanic corrosion - even fibre wrapped helicals and polymer/fibre tubular whips that just have a basic coaxial dipole within and a bare bones balun aren't immunie from galavanic corrosion.

So between galvanic and non galvanic corrosion extremes, parts will weaken over time as connected differing metals galvanically corrode and different combos at different rates, so over time not only do joints seize they also stiffen and the overall assembly looses the flexibility that stops catastrophic sheer and tear induced failures - it's never a case of 'it won't happen' just a matter of time until the inevitable.

So if looks/feels in any way less than robust assembled, look at what you can do to strengthen (by load spreading) possible failure points.

The fact you're starting with something broken means you'll want to a) make it good again & b) take precaution against a repeat since the structure will have weakens.

A crazy, in the eyes of a random observer, was how I used a dual concentric pair of interlocked home made 'slinky' like pair of fibre springs to make a slim cage to make a coax collinear of a substantial number of elements very wind resistant using them in a torsion type fashion to offset each other, cancel most movement etc.

No matter what you use, or how you reinforce or not, material failure will happen in time.

It worked well because I researched what common polymers I could extrude to make the coils from which had a low impact on parasitic resistance, inductance and capacitance.

karelgol wrote:

And it's up! Took an swr measurement with my nanoVNA from 26Mhz to 29Mhz, nowhere higher then 1.6! The lowest at about 28Mhz, 1.13!

Well done karelgol on getting an old antenna up and running well! Hopefully you will get a good few years from it.

A5H5ATAN1C wrote:

over time not only do joints seize they also stiffen and the overall assembly looses the flexibility that stops catastrophic sheer and tear induced failures - it's never a case of 'it won't happen' just a matter of time until the inevitable.

A5H5ATAN1C, you are describing my knees well there

I think some are under the impression that i repaired the broken top section. I didn't. Just used 2 broken antennas (1 at the top, 1 at the bottom) to make one complete antenna. Did nothing technical, just a layer of epoxy laquer for protecting my hands from the fiberglass splinters and a spraypaint job, just for looks.
Think i'll just fiddle around with the SWR to get the dip around 27Mhz so 26.285 and 27.555 are both as good as they can get.

73

It's kinda irrelevant how you made good the broken/damaged antenna - it works and hopefully so long term - but the logic of thinking it through and deciding whether a bit of precautionary strengthening/strain relief is necessary or just doing as a practice isn't any less of a consideration under any scenario.

Remember, as owner/op of your station (irrespective of what licensed or exempt status), you are legally liable if you make an unsafe install that eventually ends up causing injury or consequential damage to property of others as much as you have an absolute liability to make best practice decisions to minimise and reduce undue EM detrimental impact into surrounding/adjacent properties and rights of way as well as to the health and safety of you and other occupants of the station premises. It's all there buried in the terms of your license or schedule of limitations governing usage of your station, and transparently required to be addressed irrespective of if it's a formal license governed use or under license free/exempted status.

As I said in my outlines about the logic of why you should use an LPF even just as an outline precaution, anything you do to maintain an above minimum effort to make an antenna installation as robust as circumstances allows for, will work in your favour when the smelly stuff hits the fan.

I'd rather be overkill than be found to have been liable due to laziness, lack of interest in the boring bits, or worse - ignorance.

You absolutely do NOT want to be doing any strengthening to any section of the Imax 2000. It's ability to bend is what reduces stresses on the base section and where every section joins to the next. By strengthening a portion of it you increase stress elsewhere and risk creating a point of failure. Ideally you'd also mount it on a pole that also would have a bit of give in it rather than a thick walled steel one as this would reduce stress on the base section even more.

Exactly what i was thinking based on my fishing rod building experience. Reinforcement on one place can lead to breakage on another place.

They are all made to specs that include stress and strain.
So as said no extra strengthening or it will fail at the next joint.
Aerial might look like they are just thrown together but time and money is spent designing them first.