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Lightweight 40M Dipole?


#1

Hi All

As some may remember from another post, I will shortly be building a 40M version of a Rockmite for QRPp work. (approx. 500mw output)

I intend to try it out for “ultralight” activations and will carry my 6m SotaPole as well. But I was wondering about the lightest materials I can get away with for a full size 40M dipole that will stand up to “a little bit of a breeze”.

Note that I could guy the pole so the dipole doesn’t have to be “structural”

What do you think?

Thanks and 73 Marc GØAZS


#2

In reply to G0AZS:

Hi Marc,

My personal feeling is that you should resist the temptation to use a single strand wire and look for lightweight multistrand. I use cheap cable sold on eBay (supposedly as speaker wire). This has stretched a bit in practice, but is okay and after a year still does not need adjustment. The important thing is to provide some form of strain relief at the dipole centre connector and I would say that I find the SOTABeams winders excellent for keeping the dipole (mine’s a 60/40/30 multiband) in good condition. More weight, but well worth it.

73, Gerald


#3

In reply to G0AZS:

I used computer ribbon wire with a NORCAL antenna and it seemed frighteningly lightweight. It was the equiv of a 60m dipole. It didn’t break though even with some rough handling!

As you implied, I didn’t use them as guys, I guyed the pole separately.

73, Jon


#4

In reply to GM4ZFZ:
Hi Jon

Yes I have a “Double Norcal Doublet” (88ft) made with computer ribbon from Richard that I normally use (works very well) but I want to dispense with the 4:1 balun and tuner and just trim for one band.

It has survived OK so far, including a windy 3 weeks on a Swedish Island last summer during the IOTA contest.

Anyway I wondered about the wire (and the coax) and the lightest way to construct a good strong centerpiece.

73 Marc GØAZS


#5

In reply to G0AZS:
Hi Marc,
I use multistranded equipment wire from Maplins. Its very light but surprisingly strong. 100m 24/0.2 Wire Blk code CK73Q £14.99. I think that is the size I use.

I use the SOTAbeams winders too. I have one doublet for 40m and another for 60m using 300 Ohm ribbon feed also from Maplins (other sources might be cheaper) for /P.
73
Roger MW0IDX


#6

In reply to G0AZS:
The 80/60/40/20 dipole I am using is made out of 20AWG multi-strand and is quite robust although I have needed to repair the connection right at the center of the dipole. I don’t think it is too heavy although I know some do. The issue is that on rocky summits you need something that will not snap if it catches on a rock. I have picked up a couple of drum remnants at rallies in the past few months of 22AWG at 50p each, which is a bit lighter and will use that for future constructions - I could probably make several dozen with what is on these drums.
73 jim


#7

Thanks to everyone for the suggestions…
One more thing… Are you all using RG174 to feed it?

73 Marc GØAZS


#8

In reply to G0AZS:

Sorry, guilty of using RG58. Must make amends!

73, Gerald


#9

In reply to G0AZS:
No, I nearly always use twin feed. Light 300 Ohm ribbon for portable and 300 Ohm slotted (thicker) for home.

If I was using just one band (resonant antenna) I’d use RG58 for portable.

73
Roger MW0IDX


#10

In reply to G0AZS:

Hi Marc

I have used computer ribbon cable for many antennas from 20m to 80m dipoles with great success. The strength of the stuff is incredible, seems to withstand gales and I have never had the wire itself break (Having had a pole break when the antenna was set crosswise to the wind, when erecting the aerial in very strong wind I usually put one leg directly into the wind now, thus acting as a guy)

The weak point is where the feeder (and I do use RG174, no balun) joins the dipole, soldered joints are particularly vulnerable to breaking due to flexing. I have developed a technique using a three-tag tagstrip, the dipole ends being fed through the holes for strain relief and the feeder also being rigidly attached to the tagstrip by a cable tie to prevent flexing. The top of the cable is sealed with a gob of waterproof PVA adhesive to prevent water ingress. This arrangement is virtually weightless, and the one I am using at present has survived a dozen activations some in appalling conditions.

I have also used computer-ribbon dipoles with balanced feed and an ATU as in the Norcal design, but have generally found the arrangement to be less effective than a resonant dipole and of course you have the extra carriage and the fiddle of adjusting the ATU. But worth considering for a multi-band operation.

I also can recommend the “wirewinders” - they do have a small weight penalty but I’ve not had a tangle since I started using them, and they do make for very quick and easy deployment.

Good luck with the home-brew,

73 de Paul G4MD


#11

I use .5mm PVC covered stranded wire for my 10/20/40/60/80 metre linked dipole and including the power poles/perspex insulators/guys and the commercially made centre piece it weighs 70 grams. I am still using RG58 which seems to weigh about half a tonne and is about four times longer than it needs to be, so I could make a big saving there.
I also have a 60/40/20 metre version which I made first, that has been up for extended periods both at home and at various holiday cottages and has survived everything except a sash window dropping on it when I used it in a partly indoor but mostly out door configuration at a postage stamp size cottage.
I think a lot of the strength in the wire I use is in the insulation. I have had some wire of a similar gauge that snapped very easily.

I make my wire winders out of thin plastic card (scaffolding tags are ideal).

My guy system for the mast is the centre from a reel of insulating tape with three cable ties to hold the guys. The 6m fishing pole is guyed at about the four foot mark which I have found is much more effective than guying near the top as I did at first. I now use very thin but strong guys instead of the near rope I used to use and each one is only about 6ft instead of being 30ft long.

Regards Steve


#12

Hi,

Computer ribbon cable for the dipole antenna here too. Amazingly strong and of course it doesn’t catch much wind 'cos it’s so thin. Links made from PC motherboard jumpers. Fed with speaker wire as balanced feeder and a small 1:1 balun at the rig. Wire winders made from thin ply are very light. Have seen corrugated plastic house for sale signs used (GW4BVE?) also.

73 Ian


#13

In reply to MW0IDX:
RG174 feeder into choke balun (5 turns of RG174). Wire is 7/32 multistranded with Yellow PVC sleeving. Yellow stands out against a blue sky (ha!), grey,black,white clouds and against green grass, brown mud, rocks and purple heather.

Nice and lightweight and mine has survived some 70+ outings on Scottish summits and some very strong winds.

5m fishing rod is guyed separately. Also I make sure that the connections to the feeder do not bear the load or the connections will fail early.

Andy
MM0FMF


#14

In reply to GW7AAV:

Hi, Steve.

70g? Nice job! I’ll have to try harder.

For coax, I use RG316 on HF. A 7m length weighs 106g including an SMA and a BNC connector. I nearly used RG174 until I looked at the voltage rating but I think RG316 is lighter anyway and it’s certainly stronger.

73, Richard


#15

I use 24/0.2 equipment cable. It has to be stranded cable for obvious reasons.

For all construction answers, check out John G4BVEs pictures and instructions on John’s Flickr stream, you won’t find anything simpler, or in my opinion, better, it’s not rocket science.

It’s all there for you Marc, design for each component, lengths of all elements, etc. My current antenna is 60/40 only and has seen over 100 activations without problems. The secret, as someone else mentioned is to take the weight off the wire at the dipole centre and at the links, again see John’s plans. Another very important point, use wire winders and load the wire onto them in a figure eight pattern to save kinks and coil memory getting into the wire. Richard G3CWI has good photos on his Sotabeams website showing this and he will supply you with very good quality winders.
I am crrently in the proccess of gathering the components for a six band version 80/60/40/30/20/10

73 Mike GW0DSP


#16

In reply to G4ERP:
I also use RG316 but no solder anywhere - everything is crimped. A friend who worked with this stuff professionally in aircraft radio told me that solder makes RG316 brittle.
73 jim


#17

In reply to GW0DSP:

My wirewinders are made out of the corrugated plastic Estate Agents use in house ForSale signs. You can find sheets of it everywhere, especially after a windy day. It’s lightweight, strong, waterproof and free!

I think John used some thin marine ply which he profiled more accurately than my plastic. I cut the approx. shape with a Stanley knife. Took about 5 mins to make both winders which are still going strong 12 months later.

Definitely crimp and don’t solder RG-316. Good RG-174 is stronger than it looks. Good RG-174 has a copper plated steel centre conductor for strength. Check with a magnet. Make sure you have proper strain relief where the coax enters the plugs. It’s a classic failure point.

I use RG-174 for HF and for 2m occasionally. 10m for HF feeder and 5m on the 2m J-pole. I’ve not measured the loss on 70cms but when I was playing with a 70cms PA the other day (see Gerald’s thread 70cms An emerging band) I used a 3m RG-174 patch lead from the 817 to the PA. With that I got about 16W o/p. Switching to a 1m RG-58 patch lead upped the o/p to 19W. Surprisingly more than I expected.

Andy
MM0FMF


#18

In reply to MM0FMF:

Hi Andy,

One issue that I have had recently was packing cables away when it was very cold on a summit. I neatly packed everything into lightweight plastic containers at home with room to spare, but the cold made the RG-58 difficult to bend and it wouldn’t go back first try so wasting time in the worsening weather conditions. I have since repacked everything using larger containers.

I think RG-174 would be about optimum for HF relative to cost / availability, but would not wish to go any less than RG-58 on 2m. For 70cms I use 5D-FB semi-rigid which is fun to roll up, so I am thinking of wearing it like a sash (I used to do this with RG-213 in my first year of SOTA) or strapping to the outside of my rucksack. As for 23cms, I guess I need to source some more 5D-FB. LDF4-50 is a bit heavy for SOTA use!

73, Gerald


#19

All good stuff… Final question then related to my 40m single band dipole project.

For those of you that do use coax (of whatever sort) without a 1:1 balun as a centrepiece (unlikely given the weight) how many bother to put a few coils in just below the centrepiece? Is it really worth it? If so, how many and how big a coil?

Tnx es 73 Marc GØAZS


#20

In reply to all: My initial foray into HF SOTA has a stepped dipole cut for 20, 30 (in case I ever get proficient on cw) 40, 60 and 80. I used 20-strand flex for the radiator and RG58 for the feed. The radiator sections were soldered and even after a few outings are showing some deterioration. IMHO, GW4BVE’s approach using cable ties is superior as the insulation prevents a lot of the twisting.

It looks as if I may be looking at a re-build in due course.

RG58 is said to be rather heavy. Would someone please point me in the direction of a description of the other coax cables mentioned.

Manty Thanks, Dave, M0DFA/G6DTN