HAM RADIO - DXCommander vs Physics 

Spot on, Roly. I, too, had a somewhat similar experience - and learned from my mistake. I thought that I would go the extra mile and guy my DXC at the upper spreader as well as the lower spreader as instructed. The guying at the upper point made the pole more "stable" in gusty winds as only the small diameter top 3rd of the pole would flex and bend in the wind. I thought I was all set, and the DXC looked wonderful! I had also installed the 80m "L" as one of the elements and the additional guying at upper spreader minimized the "bowing" imparted from the weight of the 80m element....life was good..... Then, during a rather brutal snow, freezing rain, and ice storm, the ice build-up on the 80m element pulled down so hard that it snapped the pole at the upper spreader guy point - exactly as you show in your fulcrum-load diagram. Adding to the ice weight plus the initial element weight exerting a downward force, the accompanying wind added additional downforce making the pole crack at the stress/load point of the upper guy. Being a fiberglass pole, it only took an initial crack to weaken the pole to the point of ultimate failure. I have found two solutions....1) I only guy at the lower spreader. The pole flexes and bends in highs winds, but I've not had a problem since. 2) I ordered 2 spare poles from Callum; they're cheap as chips and I always have a spare - or an extra pole for use on experiments, portable ops, etc. And, yes, I kept the broken pole and use it for other "projects". -73-

Excellent explanation. You are correct in the wonderful customer service provided by Callum and the Team. I had a DX Commander pole damaged due to wind and received a new pole rather quickly.

Hi Roly, Sorry to see the pole snapped. Great Callum is sending one just for shipping charge. He is top notch. Nice temporary repair. Should hold up until new pole arrives. I've had two 12m Spiderpoles in the backyard strapped to wooden fence posts with wide Velco straps for about four years un-guyed and have withstood 70 mph gusts. They are being used for a terminated inverted U antenna which probably not as stressful as a DX Commander. You and Gail stay safe. 73 WJ3U

Roly, I had a too-long metal fence top rale pole that looked real suspect to bend or break much s in your case. What I did was simply slide a plastic pipe over it giving it just a little room to move but not much, that plastic not being really strong or heave became just enough to stop a bend. A short piece of plastic pipe at the stress point being mounted with the mast pole then inside it a few inches above the stress point might be just enough to stop the break. Strangely a very near hurricane-force storm came through and it held up fine, but the 3 sections vertical on it actually unscrewed and came down. The pole worked but now has to come down and be screwed back in and reinforced the actual antenna. Thanks for sharing your experience !!!.

Fascinating indeed! And I'm sure you're correct; setting a fixed 'fulcrum' at that point would prevent the entire the length of the mast from swaying, which it's designed to do. My own DX Commander, which is situated in a relatively open, relatively flat plateau on a mountainside, has managed to withstand some fairly frightening winds over the past year or so. It flexes much like the fir trees that skirt the field around it. Cheers and 73!

Wow Roly that’s some awesome engineering. Mine snapped at the same place and Callum quickly sorted me out with Warranty replacement. Now I just need you to send the doweling so I can fix the broken one.😃😂

Callum's Customer Service is the best in the industry!!!! I can tell you many stories about how great the service is... not only personally but from many friends who have brought a DXC.

I had a sotabeams pole snap this summer. Sure makes your heart sink. Thanks Callum for helping Roly out. Using poles is an art form in itself. VE6KBI.

Oof yeah, had that happen to mine too, damn you Wellington wind..

Thanks for posting, Roly. I was considering doing the same thing to keep from having guys out in the yard causing a nuisance. You saved me some heartache. Thanks so much.

Excellent video Roly… Reminded me of my days at University studying Maths/Physics 👍🏻😊

Well Roly. I have exactly the same break on my DX commander pole. Mine was zip tied in few places at around the same height as yours to a very convenient support. We had a big storm last weekend with very high winds along with a good snowfall and it appears that ice/snow had built up around the pole/wire and with those winds (some said they were 90mph or more) became too much for the pole. I've not contacted Cal for a replacement as I'm on the waiting list for the self supporting version and my temp repair seems to be working for now. 73

Totally agree with you. Pole needs at least some movement. Cal is a great guy,superb customer service! Cheers ✌🏻

I have my DX Commander guyed at the bottom per the instructions. There were high winds here yesterday and I couldn't believe it didn't break with it flexing as far as it did.

your analysis is spot on.

Totally agree with your logical thinking.. Always best to let the pole have at least some movement 😊

Wow. That's a nice video and nice explanation how this could have happened. It makes sense, that's for sure. I have one pole in the front-yard as support for my 160/60 wire. That one is not guyed but strapped down with tie-wraps. It is not secured with hoseclamps and with heavy winds it will come down automagically. Have put some spunge at the bottom to stop the hard stop at the end. It wiggles until it collapses, I try to get it down before that happens but it happened two times now that I was just too late. I've learned to do it earlier now. The DX-C in the back-yard is normally guyed - quite strict on the bottom plate, a little looser at the higher two. Not sure if I should remove one or two guy-wires...

Paul VK5PAS and I did a SOTA and tied his pole to a steal upright post at the trig point on the side of the post the wind was blowing. Paul no sooner sat behind a bush out of the wind and his Squidy broke and landed dipole and all landed on top of him. We jammed the pole together somewhat but tied it with a bungy strap to the other side of the post and the bungy could flex away from the post instead of bending the Squidy over the top of the post where it broke. Early Archimedes lesson for us on a windy summit. vk5cz..

Nice fix Roly! I guy mine only at the recommended place and no other higher levels. It bends a little if its blowy but , so far , has survived 3 years in some high UK winds. Glad Callum sorted you out a replacement. Hope to see you on a Zoom call sometime! Tom

Hi roly, hope your well. Great video. I had exactly the same situation happen here a few months ago with a pole on the fence snapping, in that spot. Again cal had another pole shipped out in no time at all. We live and learn eh. Best wishes: brian zl3xdj.

I agree wholeheartedly with your assessment. I've never had a guyed pole break, but guys can be a pain in a high traffic area like the back yard. Might hafta devise a latching mechanism that will allow you to lay the pole down for the high wind events but can easily be latched into the upright position without tools.

It looks like this wasn’t the first breakage. Seems to be a mottled mark (gaffer tape?) at the break area ….or was that part of the ‘here’s one I made earlier’ as you were making the video? Thanks for the vid. Thumbs up.

Roly, could be a combination of the fulcrum point and the number of cycles the wind blew and let up and the blew again. I still have the DX Commander that was bent to 90 degrees with blowing freezing rain without failure. Mine however was mounted on a 4 ft length of pipe 2ft in the ground and 2 ft above. I removed the rubber from the screw cap and slid the DX Commander over the (1.5 inch?) Pipe. Let's the entire DX Commander pole to absorb the side loads. Cheers.

Ouch! When I set up on the shoreline I’ve seen the DXC bend so much I wanted to take it down. Then the gust is over. I guess I’ve been lucky so far. I was amazed at how far it bent.

After reading all the comments, it would seem another video featuring some of better mounting techniques from people, might be worth watching. Cheers roly.

Great Job Roly!!!! Nice Video.

I have my mast mounted to a block wall. I take it down when we have high winds simply because of this. The top bracket acts as a stress riser concentrating the forces in the point just above the bracket , you can actually watch it in a breeze and see that it is trying to bend the most about 10 inches above the top bracket.

Paracord has some stretch, not a lot, but enough to stop the fulcrum point being too rigid. Even alloy poles can bend in high winds if they are fastened to a wall with a bracket.

How do you start a receive antenna in the menu of the ic7300? 😁

Roly try just using two pipe brackets one at the bottom of the pole and one were you had the top one. The pole can then flex between the two brackets when the top half bends in the winds . I have a fan dipole on the top of mine and has performed well in high winds 73s Tony M7CEV

Hi Roly I agree with Anthony, M7CEV, that the root of your problem is actually with the two support brackets between the top and bottom bracket. Thus you are forcing the supported section of tube to be rigidly straight until just above the top bracket. That concentrates the flexing forces across a very short length of tube, resulting in failure. If your pole were supported at just two seperated locations, then the pole could have flexed a bit, which may have been enough to resist the breaking just above the top support. This is well known in the structural analysis world. Still, I have experienced Wellington winds and seen how towers and aluminium beams fail from metal fatigue, so maybe there is nothing for it but to add some guys.

Interesting Roly, I have either been lucky or clever with mine. Have it dropped over some 1.5" Aluminium tube which is secured in the ground, has some Concrete round it now. I initially had it dropped over a Tree Stake which lasted for over 12 Months before breaking. Of course mine still has a bit of movement in it as the Ali pole flexes a bit and there is some slight movement between the Classic pole and the Ali tube, it is not a tight fit. Mine has survived some fairly high winds, I wonder do you know how strong the wind was that broke yours? I have often looked at mine and the Top sections are almost Horizontal in the Wind. As you say in your video yours and indeed mine are NOT set up in the way Callum recommends, however we do like to experiment :-)

This is more "bending moments" and shear forces that need examining....or perhaps the pole bent so much it was pushed against the corner rail of the trellis...this would deform the poles circular shape and the corner would concentrate force at that point compromising strength?

WOOOOW...Uncle Roly, did it really got that windy there it made the Fiberglass Segment breaking a half?

Very interesting. I guess that when erected with guys, the section below the guys is able to bow into the wind, reducing the shear force where it’s supported. If the guys are too tight the bottom section will be in compression, which will lower its shear strength and make that section more liable to snap. Graham G4OED

I wonder if guying the pole using bungee cords would be a good solution for high wind areas. Thanks for the video Roly. Cheers

When I was a service engineer we maintained FAX machines and ordered “warranty spares” with the 200 main shipment from Japan. Instead we received 20:complete machines. The salesman sold half of them 😡but we still had to store huge machines and after a year we had a load of almost complete machines as only the same parts ever failed. What a waste.

Hi Roly, I don't fully agree with your diagnosis. my thought is that effectively you have mechanically "shorted out" the flex in the lower section. A guyed one in a high wind has the opportunity to flex along the entire length which to an extent allows the antenna to reduce it's horizontal cross section as it leans. The same ability to feather is reduced if mounted rigidly. I have had a higher section break right above a join in a freak storm, no big deal but it is about 15cm shorter as a result. FWIW the pole and the end of my 80m inverted L section is not clamped but instead secured with paracord, not wonderful engineering but I think it gives the mounting some shock absorbing capability in gusty winds. 73

The breaking force at the fulcrum is continuously changing in magnitude and might be mitigated to some extent by attaching a guy to the very apex of the DXC and running in the direction of the prevailing wind. Might not be great for the aesthetics but has worked so far(5 years). At least, that’s what I did! M0YZT

Darn Roly, that's unlucky. Kinda guessing but I think that as you have essentially rigidly attached the bottom ~1.5m of the pole such that the top attachment point is forcing the pole at the top connector to resist both the horizontal force of the wind as well as the bending moment trying to keep it from flopping over. When installed with the ropes attached with the ring as well as the base held to the ground, these only resist horizonal forces but in opposite directions kind of like your fulcrum. Others that have it in an over sized pipe or other such where the pole is able to move a bit there is not as large of an increase bending moment applied. This allows the length of the pole in the pipe to more easily transfer loads to the base. Or you are just unlucky and have found the maximum gust that the DX Commander can't sustain.

I think it becomes an Engineering Statics problem and we had an awful lot of torque just above the top saddle.

Its not a Spiderbeam that holds up to 120km/h. I Snapped some common Fiberglass poles at around 80-90km/h Wind. That seems the Limit of nearly all not Heavy Duty poles. Mine snapped mostly on the 3rd or 4th element (count from the base) but it is also the mounting Location on my side that it snaps on this Elements.

Much head scratching, is it not Newtons 3rd law equal and opposite forces, but senior school was a long time ago. Great video as usual. M0UDB

Gidday Roly, so when are we going to see the experiments you mentioned? Just remember your broken pole will make a nice reflector...

M0OLT Grand dad said If the tree doesnt bend it will break

I think I would take another approach..........since we know where the high stress point is, I would reinforce the mast at that point for as long a distance as you could............that will move the weak point up the pole but the un-guyed moment will be getting shorter so the "ft-lbs" will be less and put less force into the pole .......will still be bendy but the thinner sections have more wigglees in them .. could be done various ways............Cal can sell a DXC Roly pole support kit for 50 pounds cheers 73 Mike K1FNX near Boston

Nice.... ... ........... ..

I guess when guyed, the pole can distribute the load and flex over a longer area too. Should you need any help with your new DX Commander, you can always "Ask Dave" for the instructions. 😉

before i watched it I knew it was because you never let the antenna flex, it was too rigid and where the clamp was became the focal point of any energy given by the wind. The top may flex but the bottom was fixed. Adding a guy system even on the direction only of your prevailing wind, I.E. for me is SW direction, would may have been enough.

Remove the middle white clamp. that way the mast can bent in an S shape absorbing energy, The middle white clamp is preventing this bending action.

Fiberglass poles strength is in its ability to flex with a wind load. If you add guy ropes at a few places and it allows the pole to flex it will be ok. You have modified the poles design when you add spreader plates and vertical wires with load' I have a had a fiberglass pole with a single wire running up it (33 foot) and it has been up flexing in 90 mph winds for over 15 years no problem.

I put 5 6foot bamboo canes up the pole just to help the bend de 2e0ree 73 brother

It’s an I’ll wind hi

get a new one and use 3or 4 guy rops in the middle

I cant watch this....