A 2m J Pole For Under £10

The 2m band has been interesting me recently, especially as a few superrefraction events have been occurring with wild temperature swings in our bizarre UK summer of 2012.

Having knocked-up a very successful and very directional 5-element quad for 2m, I found myself with the age-old problem of beaming myself out of the action in other directions!  With a good view out to sea and over the surrounding landscape, this isn't such an ideal situation unless specifically chasing contacts across in Ireland or when the skip is running further afield.

The J-pole used to put me off making it, but having this one knocked up for a few quid, I really don't know why that was.  See the lead flashing on the roof?  I connected that with a 9:1 unun and counterpoise once.  It just about got out to first skip distance, but I don't recommend it, not least for safety reasons!

So, I decided to have a go at a J-Pole for 2m.  The usual criteria applied: cheap, readily available materials, preferably those commonly found around the house or shed, and a price as low as possible.

I had a look at one commercial outfit kicking our J-Poles for 2m, and was astounded at the price for such a simple antenna - nearly £150 if you choose all the mounting hardware.  OK, it's well made by a reputable company, but even so, £150 is a lot of money for what is little more than two bits of tube.

There are a few design guides out there in interweb land, but this one is a particularly considered version, which appeared in CQ magazine at some point.  Use these dimensions and you won't be far off that hallowed ideal SWR figure.  You can find an interesting discussion on the performance of a J Pole here.

Mine ended up a shade too long, but even so, the SWR was only about 1.5:1, so perfectly usable, especially with a tiny hand held kicking out 2W.  The SWR was off only because I'd extended a shorter, random tube with a copper connector, and hadn't accounted for it's length.  I trimmed half an inch off, replaced the end cap and the SWR was down to about 1.15:1.  Signal reports are very good, so this is a keeper.

I did follow the experience of the article's author, and electrically isolated the antenna from its mount. Initially, I used a very short piece of plastic barrier pipe between two compression fittings, but this proved too floppy to use.  So I ended-up just shoving a good piece of snugly-fitting garden cane up the antenna's innards.  This is nice and stiff, and of course entirely insulated for mounting on a metal or other pole.  In future, I think I'd replace the elbows with tees at the bottom of the antenna, so that two canes or other support could be inserted, as this antenna is quite top heavy and needs good support.

Remarkably, the savings from building this J-Pole over buying a commercial version can be enough to buy a basic 2m rig!

If you have to buy all-new materials, I can't see this costing more than about £10.  I had everything lying around, needing to buy only one copper tube bend and some jubilee clips.  In effect, it can cost you essentially nothing to build, and certainly leave you with enough change to buy one of the cheaper Chinese < 2m rigs.  Quite a saving!

UPDATE:

There's a modified J pole that has considerable gain over the standard construction, known as the 'Slim Jim'.  This is just another half wavelength of copper tube added parallel to the long tube of the J Pole, and of course connected to it.  I converted my J Pole with very little difficulty - you just need a flat surface or a clamp to align all the tubes up properly to solder.  You also need a simple spacer; I used plastic tube with notches melted into them (a nasty business - do it outside!) with hot 15mm copper tube and kept in place with cable ties to keep the tubes parallel long term.

I was pleased (I think!) to find the SWR had lowered to just above 1:1 on conversion, and I didn't need to adjust anything at all.  Signal reports are good, as is the reception - repeaters at 60 miles and simplex stations at 70-80 miles have been heard so far, and it's no problem to access the most useful local repeater at 21 miles on 2 Watts.

Transformed: a J pole converted into a Slim Jim.  Valuable extra gain for another piece of copper.

  
Gain is reported to be about 2dB over the standard J Pole, which brings it in at about 5dB overall.  That means my 2W handie output gets magically upgraded to 3.8W, which is rather useful on such low power.  If you're using a mobile rig with 25W, the Slim Jim will give you 48W effective out, and on 65W, 125W effective out.

An 11dBi 2m Quad Beam for £8

There's nothing like a British summer to get hams out in the open, building antennas.  It's been so damp and dull this year, when a nice day comes along, you get through a week's worth of work in a few hours!

So, having completed the very successful vertical dipole, I built a small 2m quad with 2 elements.  The boom and supports were all made with bits of pressure-treated wood going free down the local woodyard.

Looking good in a summer sky: the 2-element 2m quad.  Good for at least 40 miles simplex on 2W.  All the wood was waste from a local woodyard, and free!

This worked really well, and got out to 40 miles simplex quite readily.  It also had reasonable F/B figures, whilst not being so directional that you became isolated from very local nets.

But it wasn't good enough, with just 2W from my handie, to get across the Irish Sea from Anglesey, as I couldn't get into a /M station up on a hill above Belfast one night.  Cue: make a bigger quad!

A really good 5-element quad for 2m is to be found (with dimensions that work!) in the ARRL/RSGB book 'International Antenna Collection'.  The author built in wood, which is a good choice if you want to make cheap antennas quickly.  Wood for internal use is fine, and will last many years, so long as you get it made into an antenna and varnished-up quickly.

It's got a long nose because I hadn't enough wood to add the final director element!  It still managed nearly 100 miles simplex on just 2W.  Total cost: £8 (wire was junk).

I Just offset the narrow support crosses for the wire on the sides of the boom, rather than drill holes for dowels as is done in the book version.  I also didn't cut notches for the wire, preferring just to use time-served cable ties to secure the wire.

Does it work?  Well, I hadn't bought quite enough wood to finish the project, but with four elements on the boom, I stuck it in the air at about 3m on a temporary pole.  It should have a gain of about 9dBi (11dBi when completed!), magically turning 2W into 9.5W (15.4W when complete).

I could hear some weak signals towards Belfast, but the accent of the operators wasn't right; I turned the antenna south of the border to find the signals were in fact coming from Co. Wexford, with EI9GGB in QSO with EI9GLB.  I made a break call - using just 2W - and was heard straight away by GGB.  I was 56-7 to him, 44 to GLB.

94 miles simplex on 2W from a £34 handie into an £8, unfinished antenna.  That's my kind of amateur radio!

A few days later, I broke the 100 mile barrier with a 56 into G8XVJ/P above Leek in Staffordshire, working an RSGB contest.  I had to wait until the worst of the 59+s around him were finished, but come on - it's just 2W from 101 miles away!  I also managed to open the GB3CP repeater in Co. Fermanagh, and even managed a QSO with GI4UHP/M, though my signal was not very strong.  Not surprising, at 150 miles!

Now with the final director added, we should be at 11dBi gain.  Time for a proper mast, too!

Mind you, I have to admit I am tempted very much by the nice-looking, lightweight 8-element 'Scorpion II' quad for 2m as sold by Cubex.  That's a very good price for an antenna of such gain (~14dB, turning 2W into an astounding 30W), so long as the UK import duty bureaucrats don't get hold of it on the way!

UPDATE:

A word about  feeding.  Most 'advice' online tells you that a 1/4 wave matching stub is necessary to bring a good match on this antenna.

This is not true!

To prove it, here's the result with the 1/4 wave stub in place, as shown on my recently OSL-calibrated SARK-110 analyser:

A 1/4 wave stub yields 100 Ohms impedance, and a high SWR.

Rather obviously, this is the wrong impedance and a fairly high, though entirely usable, 1:8 SWR.

Dispensing with the stub altogether, connecting directly to 50 Ohm coax, the SARK now yields this ideal result:

That's better!  Good impedance, and a <1.3:1 SWR.

 So there you have it!  For this multi-element quad, a direct 50 Ohm coax feed is the correct arrangement.

A Bare Bones 'I-AM' End-Loaded Vertical Dipole

Spurred on by the compact size and excellent, near delta-loop performance of the copper pipe end loaded vertical dipole, and with a warm evening on offer, I set about to make this antenna something manageable by a real human.

The aim: because copper pipe is heavy, not very wind resistant and expensive, I wanted to make the antenna very much lighter, much more wind resistant and made of stuff likely to be in most hams' sheds.

So, I had lying about:

• A 10m glass fibre fishing pole 

• Some unused 2.5m long moulded wood edging strips (a coving shape is strong and lighter than square section; round profiles are not very strong and less easy to work with in general).

• Random bits of kevlar wire and enamelled copper wire

• A good length of 300 Ohm twin feed and dipole centre (homebrew, of course!)

What I did:

Take out the top three sections of the 10m pole, as they are not needed for this design and anyway are too flexible to carry any weight.  This leaves you with a sturdy pole about 6m or so long.

Use cable ties ('ty wraps') in a cross fashion to fix the timber edgings to the pole.  I've changed this now to use simple plywood clamps using bolts and wing nuts.  This allows the whole thing to fit into the smallest of cars, with minimal set-up/down time or complexity.  Try to keep the clamps as small as possible, to keep the weight down, especially for the top end load.

First attempt at a lightweight clamp so the whole thing can go portable in a small car and not be a headache to set up or down.  It works a treat, but do keep the top clamp as light as possible, to avoid top-heaviness.

I took about 2.5m or enamelled wire, bent it in two, and scratched half an inch of the enamel off at the centre point.  I then made a small connector, initially out of flexweave (anything will do), but now recommend, for durability, you use solid copper, with a spade connector attached to one end.  I soldered the other end to the centre of the copper wire.  The whole wire was taped onto the timber edgings (cable ties are better for more permanent versions, and you should lightly exterior-varnish the timber).

Solder a small wire and spade connector to the middle of the end loads.  Makes for easy disassembly.  After a year of testing, I now recommend you use solid copper for the tag, not Flexweave or similar.

I did exactly the same for the bottom end-load.

I then took some old kevlar wire, which is very light, robust and collapses into a manageable lump that doesn't readily get tangled when you collapse the antenna.  The length was just over 5m (this isn't that critical).  Both ends of the kevlar had spade connectors put on, so that the whole antenna can be dismantled easily if needs be.

Finally, I connected the dipole centre to the kevlar wire, and used one cable tie to attach the centre to the fishing pole.  Again, I'm going to make an easily detachable clamp for this, as I don't like to clutter the environment with wasted nylon ties, and it's less convenient if you have to cut ties all the time.

Nearly down to car size.  The collapsed end-loaded vertical dipole, just a fishing pole and $2 timber edging (with wires!)  Performance of the fully-deployed antenna is just under that of a full wave delta loop on the 20m band.

Connect up the 300 Ohm twin to the ATU and: voila!  A fully-functioning low angle DX vertical dipole that collapses into a 1m-long package that easily fits in a small car.  Total deployment and take-down time: about 1 minute apiece.

Proof that this is light: very light!  An adult can easily balance it on one finger.

For mounting, I use my trusty cement mixer tripod (actually, it has four legs!), onto which a standard 2" aluminium pole of about 1m is put onto the spigot, and then the fishing pole sleeves over the pole.  It's very sturdy even in heavy winds, though some simple rope guying is best, as is putting a couple of heavy cement blocks or stones on the feet of the tripod.

This is probably going to be my permanent portable antenna, and the one that will get deployed when it's blowing an 85mph gale at home.  It performs almost as well as the full wave 20m delta loop, which is no mean feat.

The antenna working clifftop 'graveyard portable' from Llanbadrig Church, Anglesey.   On this evening, conditions were not good on HF, but I did manage the US west coast and Japan on 50W SSB.  Not bad for a made-for-peanuts antenna!

Thanks to the late Les Moxon, who inspired this design from a 2-element wire vertical beam in his excellent book HF Antennas for All Locations.  The more you read this book, the more you realise how good it is.

Incidentally, the 2-element beam is just 5m in height, needs only about 2m ground clearance, and for me, worked ZS and VK easily on the first outing, suspended - badly - from two bendy fishing poles!

UPDATE:

During a visit to the toilet, I belatedly had the brainwave of trying telescopic whips for the end loads, so that the whole thing could become even more compact and portable.  Finding good quality whips of the required length isn't that easy, but very reasonably-priced units are sold by Buddipole.

Update (2018 July):

I've started operating at a rural shack that really brings out the best in this I-AM.  I also want to start working at beaches and other places more often, as the domestic environment continues to worsen in terms of RFI for most of us, and will hit me, sooner or later.

To that end, I find that the end loads, which are effectively capacity hats, have too much mass and result in either 'head nodding' for a flexible mast and timber/fibreglass arrangement, or an antenna that is too massive overall in the case of an all-aluminium version.

The answer is to build disc-like capacity hats instead.

In early tests, using ARRL Antenna Book formulae, I could just about match the antenna with an internal ATU on 14MHz, but only above 14.260MHz.  The discs are obviously slightly too small.   I could only match-up on all bands 20-6m when the lower end of the antenna was about 30cm from the ground.  Normally, that means excessive ground coupling - and unacceptable losses.  But this was during excpetionally (as in 50+ year exceptionally) dry conditions where the water table has lowered substantially over normal levels.  In wetter conditions, the antenna would probably match at a greater height.

Even so, I did manage good contacts with, for example, A41 land on FT8, with decent (equal) signal reports both ways. A quick WSPR test for about 30 minutes also showed very good comparison with other stations.

All that said, I am going to make end discs that are a bit bigger. For this, to provide physical robustness and self-support, I've ordered some 2mm copper wire for the disc radials, and some 0.8mm wire for the outer ring.   Each disc simply slips over the fibreglass mast, making for an antenna you can roll up and carry in your hands or backpack.  More details when I complete the exercise...

And here's a wind test, when I was on-air to PC1H, DL1HA and ON9CGB, at 40mph (64km/h), gusting about 48mph (77km/h) with one rope guy to a concrete block, just mounted on a pole placed loose on a cement mixer stand (two concrete blocks to secure). I'm happy this could take significantly higher winds :

DSCN7844 from John Rowlands on Vimeo.

Following discussion on QRZ.com's forum, and a tongue-in-cheek suggestion from G3TXQ, this antenna shall now and forever be known as the 'I-AM' (!)  

Go build!

An 'I' Vertical Dipole For Peanuts

I woke up this morning with an idea about converting an old 10m dipole made of copper water pipe into an end-loaded vertical dipole for the 20m and upwards bands.

The 'I' vertical dipole is perhaps best known at the moment in the form of the very well-made and favourably-reviewed I Pro Home by Pro Antennas.  Even the price of the I Pro Home is very good indeed, and for those who don't like to build their own stuff, or want a more professional finish, then I think the following experience should give you comfort that, if you buy the I Pro Home, it's likely to work very well indeed.

But it would be wrong to suggest that an end-loaded dipole is in any way complicated in form, and can't be knocked-up in half an hour if you've all the materials to hand.  

So, with my homebrew version with its wood dipole centre, a wooden mast fixed to a fence post, and with the bottom end load pipe at less than a metre above ground, I connected up using 300 Ohm twin, although a vertical dipole is not exactly balanced, by virtue of one end being up in the air whilst the other is face to the ground.

Heath Robinson?  Absolutely!  Effective antenna?  Well, it got into Indonesia in the first two QSOs attempted.

 
In case you want to build your own, the vertical part of each half of the dipole is 2.5m long, the end loaded section at the end being 1.25m each end of the 'tee', a total end load of 2.5m (repeated for the other half of the dipole).  It is in practice just an 'I', cut in the middle to feed it.

The result?  Well, of course an ATU is necessary for this system, but that's pretty run-of-the-mill for any ham these days.  The antenna loads up nicely on every band 20-10m.  My first contact on 100W SSB on the 17m band took me, rather incredibly, to Indonesia with a 55 (QSB) into Dani, YB2TJV, with plenty of other stations calling.  That made me smile.  Much bigger stations were getting 55-57 with QSB.  Not that is means much for an antenna test, I was getting 59+ into Tomislav, the very active 9A2AA in Croatia, on the hunt for Olympic callsigns.

I've not modelled this antenna, but according to Pro Antennas, their version has a low radiation angle of about 20 degrees, which is just what we need for DX.  The contact I made with YB-land tends to confirm the low DX angles modelled.  Wholly independently, blogger EtherGeist finds precisely the same result:

Low angle DX pattern.  Excellent!

So, although copper tube isn't exactly cheap, it's also not that expensive, so I guess the total cost of my homebrew end-loaded 'I' dipole to be about £30 in new materials.  Many of us already have plenty of scrap pipes about, and if they're too short, just join them with soldered fittings, which are remarkably expensive for what they are.

Best of all, the total height of this antenna is just 6m, including a 1m ground clearance.  That is very useful indeed from a visual impact point of view and its ability to withstand the very heavy winds we get here at all times of the year.

The future?  I'm certainly going to be using this antenna more, not least because it's likely to keep me transmitting during the most severe gales of autumn and winter.  It's quite low noise, though not as good as the delta loop.  It will benefit from being made of 1-inch or 1.25 inch aluminium pole, using normal pole-to-pole clamps to fix the end loads.  This will make it much more windproof, as copper pipe does bend a bit after a few months of battering, especially with the end load making it top heavy.  The end loads could probably stay as copper, which also lends itself to portable operation in that you could have a compression fitting or two at either end (you'd still need to fit and compress the olive to the pipe, which is what does the fixing), where you could then attach and detach the two halves of the end loads.

Excellent!  Another superb DX multiband antenna for the price of a few days' shopping, if that.

Delta Loops - Disagreement Central

One of the first things I discovered about amateur radio, especially when it comes to antennas, is that there is absolutely no consensus at all on what works, and how.

Ask about anything online, and you'll soon find a war of words and opinion breaks out.

I came across the delta loop a few years ago ago, and have never looked back in terms of superb DX performance.  If I never saw another antenna again, I'd be perfectly happy with my delta loops.

So, why is it that there's so much disagreement out there?  I just had a look at one thread where supposedly-experienced hams fought it out amongst themselves to see which one could best trash the notion that a vertical delta loop with a base wire at hip height is any good for DX.

No good for DX?  Not my view.

But why are they doing this?  It must be (a) they've never actually tried a delta loop or (b) they're whiling away their lives writing rubbish for no good reason.

It seems this Ministry of Misinformation isn't limited to the forums.  There are plenty of web pages that will tell you a 20m loop, for example, can be anything from 20m to 23m long (yes, a whopping 15% variance!), and that the input impedance is anything from 200 Ohms to 100 Ohms - an even bigger disagreement.

Then we have the fights about where to feed the delta, and how that affects its performance.  Feed it at the lower corner?  Tsch!  It'll never work properly and the currents won't work out. 

So, despite having a vast number of hams out there, of which quite a few use delta loops, it can be concluded that:

(1) Nobody has a reliable web page that contains an agreed wire length for a delta loop antenna for 20m (or most other bands)

(2) Nobody has a reliable set of actual or modelled results for antenna impedance

(3) Arising from (2), there is no agreement as to whether a delta fed with coax and balun should have a 2:1 or 4:1 fitted.

Not bad for supposedly clever, licensed and experienced people!

We can argue all day, but the pole and wire you see behind me has worked all the way around the globe without too much difficulty.  Any antenna is better than no antenna remains certainly true, though a delta is not just 'any' antenna.

  According to my own experience, here is what I do know:

(1) A vertically-orientated delta loop, wire length of 21.3m, fed at the bottom corner with a 4:1 balun matches reasonably well via an ATU.  It's not ideal and probably has too high a loss level.

(2) Despite (1) above, I've worked around the globe with this arrangement.  You can sit there and pontificate and criticise as much as you like, but for most hams, having an acceptable SWR, a simple, effective wire DX antenna at low mounting heights that gets into the Pacific from Europe is their general idea of success.

(3) It's likely the impedance of the delta loop (base wire at 1.2m, apex at about 8m), is lower than what is preached by forum jockeys and experts alike.  It seems to be towards the lower, 100 Ohm end of the range than the upper, 200 Ohm.  Actual measurement by a colleague on a commercial, apex down aluminium and wire delta shows an impedance of about 87 Ohms.

(4) Leading on from (3), and from reports of the more sensible, helpful hams out there indicates that a 2:1 balun may well give a better match to 50 Ohm coax.  I'm trying this out as soon as my 2:1 arrives from the US this week.

(5) Using twin feed gives good matching on 20m-10m, but the 4:1 on the ATU does again leave the matching at a less than ideal point, though it's still less than 1.5:1 on all bands.

I'll let you know how the 2:1 works out later...