Because of where the support poles/structures are in my backyard, I've put up a doublet with 18.5m horizontals and 5m 300 ohm ribbon downlead.
Now the downlead is about a meter out from the central support and with the wind we get down here, it keeps snapping it.
The plan is to pull the antenna down and re-position it to get the downlead closer to the central pole, but I'm stuck on how to support it without the (metal) central support interacting with the downlead.
You used to be able to get, in the days of tv antennas with 300 ohm ribbon, stand-offs about 4" long that mounted to the pole and held the downlead away from it, but haven't been able to find these anywhere now.
I do plan to increase the height of the central pole to 10m at some stage (and increase the length of the downlead ribbon).
100w is the max power I can run with the equipment I have at the moment (with 10w being the norm).
Any ideas welcome.
Lateral thinking...
Metal "L-brackets" from the hardware store say Zenith 50x50 or 75x50 or even 100x75 galvanised angle bracket attached to the mast using worm drive hose clamps with something like "yellow tongue" (have seen it at Bunnings as electricians use it to pull cabling through walls [it is cheaper than the fibreglass rods etc]) or poly pipe or other UV stable plastic sitting on the bracket and fastened with a another worm drive clamp. Now we have an arm at 90degrees to the mast. Slot the end of the plastic and slip in the ribbon sealing the slot with silicone or a cable tie.
You could even slip the poly pipe over the bracket arm and drop a screw/nut through to fix in place. Paint the poly to reduce UV degradation.
Worm drive hose clamps can be opened up and wrapped around the mast then screwed closed plus they come in a fantastic range of sizes.
Have fun with it...
Regards
Bernard
I can vouch for the excellent supporting properties of yellow tongue. I had the same issue of feed line breaking at the termination at the dipole feedpoint and at the entry to the shack. About 8 years ago I added some yellow tongue to both those points and I have never looked back. The dipole has broken twice in strong winds but never at the points supported by the yellow tongue. Yes, I could probably do better at the shack entry but it has served me very well so far.
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I imagine Bernard's suggestion will last for years without the need for maintenance.
Thanks Gents.
I'll have a look see what is hiding in the shed re brackets, I'm sure I have some in there somewhere.
Love the feedline and feed through the wall Lou.
(12-12-2017, 04:32 PM)VK3ALB Wrote: [ -> ]I can vouch for the excellent supporting properties of yellow tongue. I had the same issue of feed line breaking at the termination at the dipole feedpoint and at the entry to the shack. About 8 years ago I added some yellow tongue to both those points and I have never looked back. The dipole has broken twice in strong winds but never at the points supported by the yellow tongue. Yes, I could probably do better at the shack entry but it has served me very well so far.
I imagine Bernard's suggestion will last for years without the need for maintenance.
Hello Lou
is this 'yellow tongue'?
https://www.bunnings.com.au/poly-eiger-4...r_p4430566
Note, I don't work for that mob, just posting this because I'd never heard of it.
regards,
Ian
Hi Ian,
Yes it sure looks like it. Here I was skulking around building sites looking to scrounge bits of it from sparkies and chippies. Usually found on sheets of flooring chip board. The sheets go together tongue in groove and the yellow bit is the tongue. I've also seen it in red.
Thats it. I could not locate it on Bunnings web site for my initial reply though I knew that I had seen it in store.
3.6m for $4.10...cant go wrong!
I found some in the shed here that must have been left by the builder and have had electricians pull it out of their vans when doing work for me. I have used some to make insulators for a linked dipole project.
Regards
Bernard
Thanks for the link Ian.
Next time I'm near a Bunnings, I'll grab some (although that won't be until after New Year, nearest Bunnings is 100km away)
Despite desperate attempts to stay as far away from shopping centre's and the mad silly season rush, I ended up having to go to Murray Bridge (closest Bunnings to me).
So I got 2 lengths of 'yellow tongue' (or Poly Slip as they call it) today.
In between all the Christmas do's and other things that take precedence at this time of year, I will attempt to sort my antenna out.
Thanks again everybody - Merry Christmas and Happy New Year to all.
The 300 ohm ribbon is just not up to the job, the sun is destroying it in no time flat (the insulation is just crumbling away), so I'm going to have a go at something similar to Lou's feedline in the pic's above.
From the pic's it looks like irrigation dripper feeder for the spacers, is that right Lou?
Also, what is the spacing between the wires please.
I use garden irrigation tubing with my doublet. Wire for both antenna and feedline is stranded copper 2.5mm square. Been up for 7 years and never had a problem.
The two wires are continuous (i.e. one half of the feedline and half of the antenna) to an SGC remote coupler under the eaves of the house.
Doublet is from an article in September 1984 by Rob Gurr VK5RG.
Hi Theo,
Yes I use riser tube for the spreaders but as Damien shows you can use anything that's designed to be left outdoors. Looking at his picture I think his idea would be easier to assemble than mine.
From memory the spreaders are 150mm long. Not much science went into the design but in spite of that I have an antenna that doesn't cause me much grief and allows me to be heard around Oz and into EU.
Sent from my SM-T350 using Tapatalk
Thanks Gents.
Plenty of scrap irrigation pipe lying around the backyard that can be cut up and I think there is enough wire that I made the antenna out of on the roll to do the feedline.
We'll see how this works out.
Remember "no pictures = it never happened"
Added a pix to my post above showing the centre insulator arrangement, also garden irrigation pipe.
Thanks Damien.
I've got a short piece of PVC pipe with end caps as the center piece at the moment.
It was originally going to hold the balun. Should be sturdy enough to bolt the yellow tongue to.
The arms of the dipole are attached along 3mm poly rope, so nothing puts any strain directly on the wire.
Pictures to come after I finish killing myself filling the XYL's above ground garden beds and get the feedline made up (why is it they say "Im going to..." and we end up doing the work?).
The irrigation pipe I've got is 19mm, but I know where there is some thinner stuff I can cut some off.
Yeah, the time consuming part of the exercise with homebrew open line of course is making up all the spreaders. I made a jig from wood to hold each one while the holes were drilled, at least for some consistency.
Then there was cutting the "v" shaped bits out from each end with a Stanley knife ...
Ok, managed to kill my back filling the garden beds, so not a lot of progress (on the antenna or finishing up the XYL's garden beds).
But for those that want pic's
What the sun and wind has done to the original 300 OHM ribbon:
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And somebody's watering system is now short a couple or three meters of 1/2" irrigation pipe:
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When I go over to the Men's Shed next Tuesday, I'll take the pipe with me and make a drilling and cutting jig.
The intention is to cut it to 120mm lengths and drill to 100mm spacing (or ~5" and 4" in proper measurements), giving something in the region of a 450 Ohm feedline, or so the 'net says.
Happy to change that if somebody can show a reason it should be different.
Hi Terry
The clear 300 ohm ribbon was made for indoor use. It does not cope with sun light too well as you have found.
For outdoor use you need to use the black ladder type.
But 300 ohm feeder of either type these days is somewhat difficult find.
73s
Igor
VK6ZFG
Ross at Strictly Ham does have decent 450ohm and 300ohm open feed line available. It is from MFJ and is not cheap however there is little else available that is ready to go.
Bunnings used to keep some Antsig 300ohm feed (can't see is on their web site any more) but it was really light wire. The MFJ stuff is much more sturdy. I have used some of all of the above.
Regards
Bernard