END-FED HALF WAVE ANTENNA FOR PORTABLE or SMALL SPACE USE

 

In my quest to find a convenient multi-band solution to operating HF portable I have tried several configurations, including the venerable linked-dipole for 40/20metres and full sized 20-metre-long end-fed half wave antennas. The selection of Ampro-whip antennas I own perform well from 14 MHz and upwards but become a true compromise from 7MHz and below.  My interest in using 40 metres portable has necessitated the need to use full sized half-wave antennas in both of the above mentioned configurations, which in turn requires the use of a good deal of space to accommodate a 67 foot long antenna. The safety aspect, ensuring that high voltage end points are kept above head height, means that I often need 80 feet or more of space to run an antenna portable for 7 MHz.

 

Those of us who operate portable have probably experienced the difficulties faced with utilising this much space. Hill-tops and beach-side locations are often used by other people and this leads to issues in obtaining the space needed and maintaining the safety of others on a hill-top or coastal car park.

 

My portable HF quest has therefore led me to considering antennas which use a smaller footprint. Enter the vertical antenna. Even here there are obstacles. Quarter-wave verticals of course require radials. The prospect of laying out sufficient numbers or length, of ground radials brings us back to square-one. Using fewer raised quarter wave radials (even just two or three) still requires a wider space to tie these off. These considerations led me to consider the end-fed vertical half-wave.

 

I am no antenna construction expert, very (very) far from it! So I have shamelessly proceeded to purchase an off-the-shelf solution – a Hyendfed 3 band antenna. Hyendfed, based in the Netherlands, has a very good reputation in the field of end-fed half wave antennas. Certainly the E-ham reviews (5/5 with over 50 submitted) seem to support a good deal of user/purchaser satisfaction with their range of antenna solutions. So I decided to pull the trigger and purchase their 100 watt 3 band (40-20-10) portable version.

 

 

PICTURE 1 - The antenna arrived extremely well packaged in a solid cardboard boxed and a great deal of bubble-wrap. The antenna wire, 49:1 transformer and instructions were contained within a handy pouch. A useful item for portable operations.

 

PICTURE 2 - The 40 metre coil, very well made and lightweight. This restricts the following 2 metres of antenna wire to become the much shortened second half of the 40 metre element only.

 

The first thing to note is that this antenna is a shortened version (11.85m) of a typical 40m EFHW antenna (usually around 20m in length). This is achieved by having a loading coil (see picture above) providing approximately 34 uH of impedence, positioned at the end of the 20m half-wave point (approximately 10m from the 49:1 transformer end of the antenna). 

This is followed by approximately 2m of wire until the end insulator. As you may well be aware, having a coil in any antenna, whilst allowing for a shorter antenna length to achieve resonance for a given band, has the trade-off of a much narrower 2:1 SWR band-width compared with a full-sized half-wave (see Pictures 5,6 & 7 below).  So, with this antenna it is necessary to decide if you wish 40 metres to work for you as a CW or an SSB phone antenna, although a rig’s in-built tuner or external ATU should cover the miss-match. However, no such consideration is necessary for 10 or 20 metres. The antenna produces the same radiation pattern as a half-wave dipole for 20 metres and a full wave pattern for 10 metres with a large 2:1 SWR band coverage. Please note that the manufacturers state that the longer full-sized half-wave covering 40, 20, 15 & 10m typically has a 6db performance improvement over this 3-band shortened antenna on 40m.

 

PICTURE 3 - The 49:1 transformer. This is a very small box, measuring barely the length of a disposable cigarette lighter and is very lightweight. Note that you can select either a BNC or SMA connector option.

 

PICTURE 4 - The enclosed instructions provide a useful guide as to how to tune the antenna for 40 metres operation.

 

Being able to mount this antenna as a vertical would allow me to avoid the need to cover a large footprint when portable and provide, at least in theory, some low angle radiation for DX (propagation gods permitting of course). The plan was to mount the small transformer box at a fraction above ground level and run the wire up a 12m Spiderbeam fibreglass pole, with the pole itself strapped to a sturdy tree or fence post.

 Following the mantra that you should test an antenna set up at home or elsewhere before you venture with it portable, I set this antenna up at home, strapped to a small tree in the corner of my small postage-stamp garden (see Pictures 5, 6 & 7 below):

  

PICTURE 5 – The Spiderbeam pole, nestling within a cut-off piece of sewerage pipe, which in turn is strapped to the tree in the corner of my garden. Note the small block of wood between pipe and tree to get a fairly level upward trajectory!

 

 

PICTURE 6 – The antenna on the Spiderbeam pole, fully extended at my QTH. Almost straight too!

 

PICTURE 7 - Close-up of the 40 metre coil. The wire above this is for 40 metres only.

 

PICTURES 8, 9 & 10 – Initial SWR sweep during home test. This confirmed Hyendfed’s assertion that the antenna is cut long for 40 metres. Therefore initially suiting CW operators. The sweep also confirmed the 2:1 SWR coverage outlined by the manufacturer.

 A 2:1 SWR bandwidth for 40 metres is around 100 KHz. So my aim was to adjust the length of the 40 metre wire by using the end tuning stub and reduce its length so as to centre the lowest SWR dip at around 7.140 MHz.

20 metre SWR readings were within 1.5:1 for the whole band. 10 metres was well within 1.5:1 from 28.000 to 29.000 MHz.

The day (or should I say evening) arrived to test the antenna portable. I packed my car and headed up to a local hill with a modest height of 150 metres asl. I located a sturdy fence post and strapped the spiderbeam mast and attached the antenna. Within five minutes the antenna was fully erected and the coax attached. The picture below show the base of the antenna (coax yet to be attached – Picture 11). 

Picture 11

 

The first thing I checked was the SWR. Following the home test I checked the instructions, which suggested that a 1cm change in length would alter the resonance on 40 metres by around 20KHz. With this in mind I adjusted the wire by shortening it, using the adjustable tuning stub (easy) and folding back on itself by around 7cm, with the hope of gaining a 1:1 or close sweet-spot at around 7.130-7.140 MHz, thus allowing me to have a full 2:1 or less SWR coverage on the SSB portion of 40m. As I had to complete this at home, with no further opportunity to check before I ventured portable, I kept everything crossed.

Here are the SWR readings using my trusty MFJ analyser following portable set-up:

 

Very happy with those readings. Now it was time to get on the air!

Let’s cut to the chase, how well did this antenna perform? In short, remarkably well. Remember, the 40 metre portion of the antenna is much smaller than a full half-wave but even so I found making contacts into Europe very easy on my 50 watts. I gave myself the challenge of trying to make as many contacts as possible in a 7 minute burst on 40 metres using ‘search and pounce’, here are the results:

Frequency         Callsign               Time (UTC)             TX                RX

7153                 YP19VW             17:57                     59                   59

7172                  HB9HLM            18:00                     59                   5+20

7129                  RL5A                  18:02                     59                   5+10

7177                  IK6BGJ              18:04                     57                   5+10  

 

Four consecutive 40m QSOs into Europe in 7 minutes is not too bad. What is also worth mentioning is that on each occasion the contact was made on the first attempt and (with the exception of IK6BGJ) in competition with other European stations.

With the greyline approaching I switched quickly to 20 metres and enjoyed some good DX contacts including:

W8VLN in Ohio (TX 56 RX 57)

7X3WPL in Algeria (TX 58 RX 59)

PY5QW in Brazil (TX 56 RX 59)

PV8AL in Brazil (TX 58 RX 55)

KP4EYT in Puerto Rico (TX 58 RX 59)

Other European contacts followed on both 20 and 40 (sadly 10 was closed), with my most pleasing contact on 40 metres rounding off the evening:

J69MV (St. Lucia) TX 58 RX 55

Overall I think this antenna performed remarkably well. It ticks the boxes for portability and ease of operation. Simply get the wire up and plug in your coax to the rig. To get two new DXCC for me (Puerto Rico and St. Lucia) was a big bonus and rounded off an enjoyable evening working portable with a small footprint. Sure you can make one yourself and it would be a fun project. If however like me you need an off the shelf, extremely well made alternative, then give one a try.

 

73 – G5TM