End Fed Half Wave? Convenience over Performance.?
Every antenna “Works”, you can make contacts… but how well???
I have found my end fed half wave to be a really convenient antenna, it covers all bands on HF although I use a little bit of my ATU on 2 or 3 bands just to improve it a bit. I like using my ATU as I can see the meters move and that tells me power is getting out. If I see the reverse power meter moving I know the wire has fallen down or something is wrong. I found a loose connection in my transformer box once so it is always a good idea to continually check how any antenna is behaving; not just the SWR but also is it hearing signals and are people hearing you.
So, I have been really happy with my EFHW and I set out to bag a hundred countries on FT8, just to see how it was performing. FT8 is particularly convenient because (a) you don’t have to talk to anyone and (b) linking the Gridtracker application to WSJT-X allows you to build up a map of who you worked, and you can click a button and quickly see who has heard your transmission. I feed my logging program Log4OM from Gridtracker and it gives a more detailed map of the station you’re working. A nice setup, although I am still learning… (always true!)
I had thought about repeating the 100 countries target on all bands to more fully test the antenna but currently have only used 17m. I also installed LOTW and use it to get confirmation. But I have come to some conclusions, even after only using 17m and thought I would share them with you.
The performance on 17m is a testament to the effectiveness of FT8. I have made many contacts and got my 100 countries in 5 or 6 weeks. I have only LOTW confirmations from 91 so far but have 115 in the log. I now spend little time on the band unless a new country comes up. I do call CQ occasionally as this is only fair to the other stations wanting Northern Ireland, it’s a bit immoral to just lurk on the bands and grabbing what you want without giving back.
The map in figure 1 shows the distribution of countries, and I was delighted to bag Alaska, New Caledonia and the Falklands of course. Note that a quirk in Gridtracker is that not all contacts are plotted, if you tail-end a station that has just sent RR73 instead of waiting for a CQ then Gridtracker will miss the gridsquare, but log the contact. I am not an experienced operator, although I suppose FT8 hides this from people.
I noticed that I had not many contacts from Norway, Canada or the African continent. Conclusions from data can be, well, inconclusive! I don’t how many hams were active in these countries but I “have a feeling” I should have picked up more. In hindsight I should have simultaneously monitored the online SDRs at http://websdr.org/ and http://kiwisdr.com/public/
So I got to thinking, the EFHW is really convenient for me, my shack is at one end of my property and feeding the antenna at its end is handy. Also a single thin wire is almost invisible and being inconspicuous is important, Shirley, my wife, runs an AirBnB cottage beside us and keeps an exceptional garden, not to be tarnished by ugly antennas.
Figure 1: Most of my FT8 contacts on 17m over a 6 week period (Yellow squares)
What is the performance of the EFHW on each of its bands? It is just a half wave antenna on 80m, albeit fed from the end. Once the current is in the wire it acts like a half wave dipole, the well known figure of eight, smeared out a bit because it is only at a height of 10m (probably 9m at the tips and drooping to 7m in the middle – I haven’t tensioned it very tightly). On the higher bands you get extra lobes, the easy to use antenna modelling package MMANA-GAL (from http://gal-ana.de/basicmm/en/ ) can plot these.
EFHWs can be difficult for modelling packages and it is important to add a small counterpoise of 8 feet or more so that the feedpoint works in the software, in real life I have a choke 8 feet or more down the coaxial feedline. In addition you have to change the feedline impedance in the software from 50 Ohms to a very high value, EFHWs use a 49 to 1 impedance transformer (with 7:1 turns ratio) so a value of 2450 Ohms is appropriate.
I won’t labour how to use MMANA-Gal here as I have used it in several other articles in Contact. The four main screens of the software include the “GEOMETRY” Tab which gives a table of measurements of the wires and the feedpoint, you can nearly visualise the antenna from this in the table in Figure 2. Note you should alter the 20m a bit to tune either the CW or SSB parts of each band, mine ended up as 132 feet, a few feet short but that is the length of my narrow garden.
Figure 2: Part of the “GEOMETRY” tab in MMANA-GAL
Figure 2 shows the “VIEW” tab which draws from the table in Figure 2.
Figure 3: The “VIEW” screen, you can rotate, pan and zoom this with your mouse.
The red dot is the feedpoint – described as W1B as it is at the beginning of wire 1
You use the “CALCULATE” tab to run the model on a particular frequency and it will give you its impedance and SWR as well as allow you to view the antenna’s directivity using the “FAR FIELD PLOT” tab. The calculate tab allows you to specify additional height, the type of earth and wire. I used no additional height as I had drawn the antenna as it is installed, I picked “real ground” and copper wire. If you want to run the model yourself and don’t want to draw it, save the lines in figure 4 as a text file with an .maa extension and just load them into MMANA-GAL
Figure 4: the text of the .maa file needed for MMANAN-GAL to work
Here are the results at different frequencies; figure 5 is for 80m (3.550MHz)
Figure
5: Plots for 3.55MHz (80m).
The right hand plot is from the side, you can move a cursor (red dot) around to see what the gain is at a particular take-off angle, at 20 degrees it is 0.9dBi. Actual gains do not matter except to compare with other parts of the plot, if you transmit 100W then a bit goes this way and a bit goes that way. You can slice the right hand plot and view it from above in the left hand plot- the default on the left hand plane is to show the view from above. The plot pane has an “ELEVATION” button to allow this. Take off angles are important, you get good DX at angles of 5 to 7 degrees. The plot varies as you raise the wires, so get your antenna up as high as you can – half a wavelength is great but only achievable on the higher bands unless you are very rich.
.jpg)
Figure
6: The 40m Band, note the null at the “waisted in” part of the
plots
We can also display a 3D picture, although it is easier to see (and rotate!) when its on the PC screen rather than the paper here. Any stations that lie in the direction of the nulls might be 100 times weaker ( > -20dB )
Figure
7: The 17m band on a 80m EFHW (40m long!)
And a 3D plot at 17m;
.jpg)
Figure
8: a 3D plot at 17m for the 80m EFHW
Now, as my antenna runs SW-NE I can see that some of my nulls point at Norway and this explains why I get few contacts in that direction. I’ll keep the EFHW for convenience but I am now building a CobWeb out of thin fibreglass rod and thin wire to minimise visual pollution. I will use thin sprectra line to “stay” the rods. As a sailor, this is how we keep masts up in gales, I hope I can make a superlight weight Cobweb that is almost invisible when erected. I also have some bamboos and might make a clunky portable version. More later…
Ian, 73 de MI5AFL
Blog at http://MI5AFL.blogspot.com
References and Reading:
1 Online SDRs at http://websdr.org/ and http://kiwisdr.com/public/
2 MMANA-GAL (from http://gal-ana.de/basicmm/en/ )
3 Callum’s Youtube channel ( https://www.youtube.com/@m0mcx ) - look at his playlists for antenna modelling, he has three introductory videos there.
4 https://mmana.home.blog/ has some good examples, including a cobweb
5 https://sz1a.org/en/featured-articles/end-fed-half-wave-efhw-antenna-modeling-with-mmana-gal/ is an interesting read on modelling an inverted-V EFHW
