HB9SL – An effective antenna for portable QRP on 14 MHz
The antenna described here is ideal for long-distance communications on low power, it wins over a quarter-wave vertical with dozens of radials, an end-fed half-wave vertical and a high dipole. Developed by HB9SL (Fritz Demuth, SK) it’s called the ” Vertical Polarized 2 Element ” VP2E antenna.
The HB9SL antenna has the following features: it emits at a low angle towards the horizon, about 26 ° (effectively 20 – 40 °), it has vertical signal polarisation, and the antenna gain is about 3 dB! The antenna does not require a Balun and, most importantly, high masts. The radiation pattern is almost circular, a small maximum exists away from the feed point. For this version of “Vertical Polarized 2 Element”, a mast a 4.2 Metre fiberglass pole was used as the mast.
For 14MHz a run of wire with a length of 20.8 meters is fixed to the top of the mast exactly at the midpoint. Wires go down and are fastened with cords to pegs with antenna ends raised off the ground. On one side, a distance of 6.3 meters from the end of the antenna, a break is made, a plate is inserted to form the insulator and a 50-ohm cable is soldered there, no Balun is necessary, the centre core of the coax is connected to the longer section and the braid to the shorter one. In this build the length of the coax was approximately 7 meters (avoid the coax being a ½λ long). The HB9SL antenna design was tested with the program MMANA, which showed that sometimes the feed point is better moved a little higher than in the author’s design. Since the weight of equipment is important when portable, chose a wire which is light, flexible, and does not tangle or break easily. Due to the fact that the HB9SL antenna does not need a high mast, it is wind-resistant, in practice it turned out to be sufficient to use one extra guy rope (the antenna wires formed the other two) . Please note that the mast of this antenna should only be non-metallic. A fiberglass mast fits this role perfectly. The red arrows in the diagram show the angles of maximum radiation.
Measurements of the SWR using an MFJ-259 analyser gave the following readings: 1.5 – 14.0, 1.1 – 14.1, 1.7 – 14.3 MHz. The resonance is quite sharp, so after constructing the antenna, it must be trimmed to the required frequency within 20m. Sizes for other bands. For 7 MHz, you need a mast height of 6 meters, the total length of the antenna wire will be 41.8 meters. The length of the wires to the middle 20.9 meters. The feed point is located at a distance of 15.4 meters from the lower end. The lower ends of the wires must be raised one meter above the ground. Everything else is as described above. For the 3.7 MHz band, a mast height of 7 meters is needed, the total length of the antenna is 79.8 meters. The length of the wires to the middle are 39.9 meters.The feed point is 32 meters away from the lower end of one of the elements. The lower ends of the wires must be raised 1 meter above the ground.
Nadir EY8MM (Tajikistan) – in Jan 2007 built a Vertically polarized 2 Element (VP2E) HB9SL 160m antenna
L1=L2=0.495 x WL
L3=0.3 x WL
H1=0.18 x WL
H2=0.0285 x WL
He used all standard dimensions except the height. In his case H1 was 55 meters. Top band conditions were not very good. He only had a few QSOs, the highlight was being called by SU9HP in Egypt for a new country for him. He states that the antenna showed reasonable directivity (see diagram above). Then he tried the antenna on 80 with an antenna tuner and worked over 80 North America stations! Including OK, MS and KY states. Setup was an IC756ProIII driving an Acom 1000 amp (800W output due to low mains supply voltage).
Click vp2e-calculator to download my Excel calculator to insert your own frequencies.
Tests 17th. January 2019
Once the snow had started to melt and before the next storm front arrived, I managed to set up the antenna temporarily in my garden. The centre was supported by the flag pole and the ends tied off to two trees. Not an ideal set-up but good enough to test. I have deliberately cut the wires long and my first check had the antenna resonant at 13.395MHz after first folding back and then cutting off about 6” from the longer length of wire and 3” from the shorter one, I got the resonance to be around 14.285 MHz as I wish to operate SSB QRP with this antenna. That said at this setting the antenna is less than 2:1 across the whole band as proved by my test using a WSPRLite unit running 200mW. I was quite happy with the results:
Consistently into the US south east, Ireland, Iceland and also Greece. The antenna was running roughly NNW-SSE unfortunately I don’t have enough room to be able to turn the antenna around to check it directive abilities. That will have to wait until I can get it onto a large open SOTA summit.
Directional Testing – Friday 1st. February 2019.
Well I finally decided to give up trying to find a wide open space in the country to test out my new antenna. The amount of ice and snow around means that the places I would like to use are simply not accessible.
I decided to test to see if there was ANY directivity from the antenna at all in my garden. With limited space and buildings all around this was never going to be a conclusive test and bad propagation conditions also meant the number of stations receiving my 200mW signal from a WSPRlite transmitter was going to be low as well.
Rather than hope for a better location and better conditions however, I decided to go with what I have. So using the convenient flagpole I raised the centre of the antenna up and then ran the long side (i.e. the side without the feed-point in it) across our common car parking and garage access area, fastening off the cord on the fence on the other side and then hanging a yellow cloth on the spot where someone coming out of the houses might walk into. Luckily no one came out or went in during the tests as, as well as possibly de-tuning the antenna there may have been some time taken up while I had to explain what I was doing and why.
The other side of the antenna sloped down from the flagpole almost (but not quite) in-line with the other side of the antenna, under (but not touching) my tilted over VHF steel mast and the cord tied off to the fence.
The positioned the antenna wire roughly from West to East, with the feed-point on the eastern side, meaning the antenna supposedly will have some gain to the west.
I now connected up the WSPRLite unit, synchronised its start against an atomic clock App and let it run for about 10 minutes before stopping it and then moving the ends of the antenna around. The end that had been across the car park pointing to the west moved into the garden and ran out to a tree in a northerly direction. The eastern end of the antenna now should move to the south. Unfortunately there is no enough space in the garden to fit this in and the compromise was that it ran SSE rather than due south and then the end of the wire hung down in the tree after going over a branch. This was the side of the antenna with the feed-point in it, so the antenna should now have some gain in a “sort of” northerly direction. After the 10 minute break to move the ends of the antenna I ran the WSPRlite for about 10 minutes again.
Here are the results from the WSPRnet site:
As the data is in reverse sequence, the top six entries are from when the antenna was “beamed” ‘sort of’ north and the bottom five entries from when it was “beamed” west.
Luckily we have reports from Iceland in both batches and so we can compare those.
Averaging the readings into TF while the antenna was “pointing” west we get an average signal of -18dB comparing this to the average of the signals when the antenna was “pointing” NNW-ish which was -12dB gives us a difference between the end-on direction and the side-on direction of 6dB. That is more than expected and could be caused by Iceland being in one of the side nulls of the antenna pattern or (more likely) by the various obstructions around the antenna.
These results suggest the antenna is directional to an extent but the results are not conclusive and a test in a truly unobstructed location is really needed. It is also possible that in the 10 minutes taken to “rotate” the antenna, band conditions could have changed.
While packing away the antenna, I measured the short and long sections of the antenna as previously trimmed to give resonance on 14.285MHz using an antenna analyser and the short section is 6.32m long as compared to the calculated 6.30m and the long section is 14.75m long as compared to the calculated 14.48m – so fairly close. The actual length is affected by the velocity factor of the wire used, however I am fairly confident that should an antenna be cut exactly to the settings found using the calculator, it would indeed be “close enough” to work.
Bill of Materials
– parts from Sotabems.co.uk (parts for any one band 10m – 80m)
- Thin light antenna wire (100m reel) Price € 9.22 (Hi-Viz yellow recommended).
- Centre wire support for top of mast Price €2.18 (5 pack)
- “invisible hardware” (Feed-point T + 2 x end insulators) Price €3.26.
- Coax feed-line (10m RG-174A no plugs fitted) Price €8.88 (add required BNC or PL259 plug yourself (a BNC plug costs €2.18 from SOTABeams)).
- Guying pegs (metal) Pack of 3 Price €1.68
- Cord (Hi-Viz recommended) Price €9.50 for 50m (need < 10m).
TOTAL COST OF COMPONENTS: € 36.90.
OR …… Simply buy the Linked Dipole kit at €17.04 and add the mast top insulator (nr. 2 above) €2.18, antenna wire (nr. 1 above) €9.50, feed line coax (nr.4 above) €8.88, and a BNC plug €2.18. Total cost € 39.78 and you get two winders to keep the antenna tidy and If you want to try to make a multi-band version you already have the link pieces and crocodile clips.
– supply your own mast or buy the appropriately sized one from SOTABeams (Tactical, Tactical-Mini or Mini-Mast). Or hold up with a rope over a tree branch connected to the centre wire support.
So what now ??? – Multi-band.
Well while awaiting the weather to improve so that I can get out to a SOTA summit to test the antenna out and especially to see how directional it actually is, I wondered if a linked version of the antenna would be practical. In a similar way that you can have a linked dipole. So I got busy and came up with a calculator to give me the needed lengths for the sections of the antenna to possibly make it into a 5-band antenna.
To start with I decided to build a second antenna with just one link in each side so that it would operate as either a 17m or 20m antenna. This would prove whether a linked version is practical at all.
The initial build was simply a 17m version of the antenna and I would add the “extensions” for 20m once I knew the 17m was working correctly. The build was straight forward and I thought it was going to be “easy-going” – hey even the snow had stopped, so I could get out into the garden and hoist the middle of the antenna up the flagpole. I attached the Rig-Expert antenna analyser and trimmed the antenna to get it resonant on 18.1MHz about the middle of the 17m band. The problem was that the SWR was somewhat high at 3:1 because the impedance was only 18 ohms. How could that be? The 20m version didn’t have these problems!
I had seen something similar years ago and believe it or not, it’s the length of the feeder! the RG-58 coax was about 8 metres long forming a half wave on 18MHz – crazy but true.
So I took everything down and that evening added a new longer length of coax – this time the small RG-174 type and when I tried the following day …
At this point it started snowing again, so I decided to pack up and come back another day …
I removed and resoldered the plug on and also prepared the 20m extensions as I knew the 17m antenna section was the correct length. Although I had needed to trim the antenna to make it resonant on 17m, I went with the dimensions from the chart for the extensions and …
I put the WSPRlite on this antenna to compare its performance with the non-linked version but the bands were not cooperating and I got no reception reports at all on 20m. On testing later on the main station antenna, it also got no “spots” the 20m band was totally “dead” at just the wrong time!
Before packing the antenna away I saw some strange readings
What I think has been proven though is that it should be possible to build a 5-band (20, 17, 15, 12, 10m) version of the VP2E with links to switch bands. It should also be possible to add traps but at 1.7dB loss per trap this is probably not a good idea when using the antenna portable with a QRP rig!
Final garden tests – linked VP2E 13/02/2019
At last some sunshine and after replacing the BNC plug with a PL-259, I put the antenna up on the flagpole again:
As you can see, it’s still 2:1 SWR because of that 34 ohm impedance – Perhaps I have the ratios wrong (driven element to reflector) perhaps the fact that it’s “Squished” in the garden over a metal fence and snow has something to do with it. For now it’s working and not erratic on the analyser. In fact I then connected my SOTABeams WSPRlite and got the following results immediately:
The next step is to try the antennas from a SOTA summit later this week. If that still gives a 2:1 SWR I’ll look at what happens when I move the feed point higher up the wire, this may be the issue as both examples that I have at the moment show the same SWR and this has be suggested in articles on the web.