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.