Friday, August 7, 2020

40m wire antennas compared

Before going on holiday I managed to get some life into my old C-Pole using a new home made choke. I re-tuned the antenna (with some challenges) but did not get a chance to use it. 

In the past I did use it quite a bit and was pleased with the results but as always - this does not tell you a lot. HF conditions vary too quickly and dramatically to base any evaluation on single antenna experiences. You really need simultaneous A/B testing.

A gap in my schedule allowed me to go out and do some testing of different wire antennas for 40m. I ended up testing a C-Pole versus an end fed halve wave more or less vertical and the same C-Pole versus an inverted V dipole.


Test setup

I used two identical WSPRLite beacons that transmit with 200mW on the WSPR frequency. 

  • The C-Pole was set up so that the feedpoint was at approx 2m above ground (that would be your typical setup with a 12m pole, like the Spiderbeam I have - with the top of the antenna at 11m). 
  • The EFHW was attached to my 18m pole and therefore almost vertical. The last 3-4m I set up sloping so that the feedpoint was at approx 1.5m above ground.
  • The Inverted V was set up so that the feedpoint/apex was about 13m high. 

The test period was the end of the afternoon. Not the best time for 40m and certainly not the best time to test DX performance. However it was the time I had available. 


C-Pole meets EFHW vertical

The first run was the C Pole vs the EFHW vertical. I let the beacons run for about an hour. After that time I had:

AntennaTransmissionsSpottersSpots
C-Pole1560328
EFHW1560392

On first glance the EFHW vertical seems to fare better. It has been heard more often. However both antennas reached the same amount of spotters. So nothing too dramatic here.

Now looking at the SNR reported by the spotters there is more to say about the difference.

Let's start by looking at the raw data of reports by the spotters (plotted by the distance from my test location).

The orange dots seem to go higher (SNR in dB on the Y axis) at every distance (in KM on the X axis) but with all the individual dots it is still a bit messy. 

I then averaged the reports per spotter to decrease the amount of data points. Again it looks like the EFHW performs better.

Finally I calculated the average difference in signal strength per spotter of the EFHW over the C-Pole. This clearly shows the EFHW beats the C Pole on almost all distances and sometimes by a fair margin. The outlier is S51RS at 950km. That is the only spotter favoring the C-Pole significantly.

So if you have enough height available the EFHW is the one to choose out of the two at least for the ranges tested today. This is what I expected from the theoretical analysis I did some time ago.

An interesting followup would be to see how the EFHW would perform with the same top height (sloping from the 12m pole or tree branch). With a slingshot one can easily get a vertical wire up 20m, so I would normally aim for that height with this antenna.

C Pole meets inverted V dipole

Now how about the inverted V? This one adds another element to the game as it is horizontally polarised (as opposed to the vertical EFHW and the C-Pole).

I chose a height around 13m (not fully extending the 18m pole). In retrospect I might as well have gone 2 meters lower to compare the antenna if set up on the same 12m pole as I used for the C Pole antenna. Here we have a slight advantage for the inverted V.

Running the beacons for just under an hour I had:

AntennaTransmissionsSpottersSpots
C-Pole1045202
Inverted V1146219

The inverted V got one extra shot so it is hard to tell from this first glance which one performed better.

The raw data again gives a picture that is hard to interpret quickly:

So moving on to the average per spotter. This shows that the Inverted V seems to beat the C-Pole on most occasions. 

Moving one step further the indication is confirmed. The Inverted V wins almost everywhere. The biggest outlier again is S51RS.

Conclusions

I did not test the inverted V against the EFHW vertical directly. However looking at the differences per test, using the C-Pole as "a reference antenna", there does not seem to be a lot of performance difference within EU. I would have expected the inverted V to do slightly better than the vertical on the shorter distances (with its higher radiation angle) but that might be only noticeable on even shorter distances.

So, this time I learned that within EU the C-Pole loses against an inverted V at more or less the some top height and loses against a vertical EFHW with the feedpoint at more or less the same height. 

One question remains - as the antenna's have different radiation patterns - would any of these clearly beat the others on multi hop DX? The simulations I did previously would suggest that the C-Pole would have an advantage over the inverted V because of more low angle radiation.

If it turns out the C-Pole does not "deliver on promise" there, then I cannot see a lot of situations where I would choose it over one of the other designs. Only if the footprint needs to be minimal and height is restricted (*).

This last question requires a new test around gray line time - when I can't use my favourite test ground as it is only accessible in daylight. Something to put on the "to do list".

*) Another one: would the C-Pole beat a shortened 40m EFHW of equal height - so approx. 12m? I have such a wire with spool that I used in the past for my 10-20-40m EFHW.

7 comments:

  1. Interessant Lars, heb een tijd terug een H-pole getest. Kwam zo een beetje tot dezelfde conclusies. Ik heb ook een 3 band endfed en vind dit aan een 12m hengel verticaal een erg goede antenne. Op 40m doet hij zeker niet onder vergeleken met mijn 2x20m inv-V. Echter dat is op TX en niet op RX, dan ontvangt de inv-V toch een stuk beter. 73, Bas

    ReplyDelete
    Replies
    1. Tks. Ja een directe vergelijking tussen de EFHW en de Inv V is ook een leuke. Ik heb wel met de C-Pole en de EFHW een ontvangsttest gedaan met mijn radio (voordat ik de beacons aansloot) en daar zat niet heel veel verschil tussen. Misschien een halve s-punt in het voordeel van de EFHW.
      Maar ander tijdstip ga ik zeker ook nog een keer doen. Hele korte afstand of jij hele lange zou nog wat verschil moeten opleveren (theoretisch).
      Ik zou wel een tuin willen van een paar hectare om dit structureler te kunnen doen....

      Delete
  2. Leuke test !! Ook interessant om een "ordinaire" kwart golf vertical eens te proberen. Die past nl. in zijn geheel vertikaal langs een 12m Spiderpole. 2 elevated, tuned radials zijn voldoende. Ik verwacht dat die het voor de langere afstanden (veel) beter doet dan zo'n C-pole. Tunen gaat ook veel sneller. Eerst de radials afspannen op de gewenste hoogte en die als dipool aansluiten en tunen tot X=0. Daarna het vertikale deel afstemmen zodat de gehele antenna in resonantie is. Z is dan vaak in de buurt van 50 ohm. Laatst gedaan voor 30m. Half uurtje werk max.

    ReplyDelete
    Replies
    1. Zeker ook een leuke ja. Ik heb nog een (draad)vertical met 4 radialen liggen voor 80m. Die zou ik met een koppelstukje multiband kunnen maken (als in: 40m met verlengstukken voor 80m). Naast tijd moet ik hiervoor nog een goede plek in de buurt zien te vinden waar ik na zonsondergang aan de slag kan. Ik had een mooie open plek bij een industrieterrein maar die is helaas volgebouwd.

      Delete
  3. Iam not sure about the details of the analysis. I think you should select a number of known good-performing receiver stations, and use only those for comparisons.

    ReplyDelete
    Replies
    1. Hi, I don't think I understand your point. What is a "good-performing receiver station"? Especially in the range where both antennas are heard I like to have as many receivers with as many data points as possible. 73, Lars / PH0NO

      Delete
  4. Hi, Lars!
    I didn't understand anything, but the pictures and diagrams are beautiful!
    :-D

    ReplyDelete