What antenna options (that are realistic for SOTA use) will give improved performance compared to an EFHW?
(Carrying masts and large beam antennas is not practical.)
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Hello 9N7AC
As an activator I have always favoured home made link dipoles for HF SOTA over the half wave end fed, whihc I have only used once or twice. Having said that, as a Chaser some of the regular half end wave end fed QRP signals out out by activators in Europe are excellent.
Last year I decided to make two OCFD dipoles up using the cheap 4:1 balun kits that SOTABeams sell with some available wire that I already had. A short one cut for 20/10m, and a longer one cut for 40/20/15/10m, both fed with thin coax RG-174. These are also successful on top of a lightweight 5.5m travel pole as an inverted vee, but I do not use modelling software so I cannot compare theoretical performance with a half wave end fed. All I know is that I made 100s of QSOs with these antennae when I was in Germany activating for 8 days in June /July. Good luck, whatever you decide to use as an alternative to the half wave end fed.
73 Phil G4OBK
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Hello,
Not sure what you are looking for. Directivity in a specific direction, lower radiation angle, reducing losses, better NVIS diagram , front to back ratio etc, to be compared to an EFHW installed vertical, in Vee, horizontal, low, high ? For 10m, or for 40 m ?
73 de Pierre F5MOG
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@G4OBK Thanks. I did try making a standard dipole for 20m using some twisted pair solar battery hookup wire and a knot in the wire at the center, then using the twisted pair as feedline down to a binding post adapter at the radio. Unfortunately the VSWR was terrible. I simply could not get it tuned.
RF parts like toroids are simply not available in 9N so a balun is out of the question!
@F5MOG Reducing losses is a high priority. Directivity would be very nice. NVIS is not much use in this part of the world unless I want to limit my contacts to VU and B. Installation and polarisation are constrained by the need to use whatever “antenna mast” nature and/or local architecture make available. Perhaps I can get a fishing pole.
Single band 20m or multi-band 20-10m.
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Hi, yes, I’ve been caught out by that as well. The problem is that the characteristic impedance of the twisted pair is typically higher than the approx 50 ohms impedance at the centre of a low slung dipole. Using a coax feeder will solve that.
If you just want a single band dipole, though, make the twisted pair feeder an electrical half wave long, then the impedance at the radio end will be the same as that at the dipole centre.
I started out on HF SOTA using this setup on 30m. For 20m, you would need a length of a bit less than 10m (allowing for the velocity factor of the twisted pair). For a short support pole, that might leave quite a lot of feeder on the ground, which is best avoided as it introduces loss…
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Making the feeder 1/2 wavelength is a good idea, I will try that.
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To improve the performance of any antenna, you might want to consider the slope of the ground where the antenna is set-up. Basically you want ground sloping away towards the target area.
Here is a link to a discussion on the topic
Ian
VE6IXD
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I also ran into the same problem using speaker wire in my first dipole kit, and switched to using RG-174 coax instead (which is probably as easy to obtain in 9N as the toroids).
Now I am experimenting with some low loss 75 ohm cable, and am using 1/2 wave on 40m, which is also 1 wavelength on 20m. It works quite well, although with velocity factor correction that’s about 15m, which is rather longer than necessary for portable work. A half wave on 20m will be better, probably in the 6.5m to 7.5m range, depending on the velocity factor.
I have a list of various feedline types (and typical losses) here:
https://practicalantennas.com/feeding/cables/
Note the losses for the various types of “speaker cable” in the second table : this is a problem on the higher bands with plastics that are not designed for RF use. I suspect that the cable you are using may be similar. If you can find a piece of CAT5 or similar computer network cable, the individual twisted pairs are 100 ohms, and have lower losses at HF.
There are some other options, but I need to go get breakfast.
Meanwhile, I will ask a local Nepali friend when he will be heading back home for a visit…
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Interesting you are going in this direction.
I used resonant linked dipoles for 40/20m for many years.
I was then tempted to try an EFHW . following the success of others.
I’ve never looked back!
I use a KX2 with built in tuner.
It easily tunes 40/20/10. It will tune 60m.
I mostly work 40/20 ssb and have never failed to get enough contacts to qualify.
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Without toroidal cores it will be more difficult… You connect a symmetrical antenna to an asymmetrical output (antenna socket)… you should use a balun. (Balun = balanced → unbalanced)
Have a look on the internet for “ugly balun”
The “Bazooka” antennas might be something for you - they are made of coaxial cable.
73 Armin
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Yes, it’s difficult but doable.
For several years I’ve been using LC matched end fed half wave antennas. By definition they are mono-banders. So far I’ve built three antennas for 15/12/10. Idea is not original - I’ve read about it here , but ended up with completely different L and C values.
I’m using iron-powder cores for the inductor, but air wound coil will work just fine. For the capacitor I’ve used a piece of coax cable.
I’m supper happy with results - each activation from EA8/CT8 with 10W CW yields 100+ contacts. I deploy these efhw antennas in a vertical configuration, with 2m coax, no tuner is needed - SWR is sharp 1:1, but it took a while to figure out the length of wire and LC values to achieve this. Some pictures:
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If you have trees at your location you can use those instead of a mast for an inverted V dipole, or even a 1/4 wave vertical.
Getting the ends of the antenna above the ground (EFHW or dipole) should help with performance.
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You have not defined what “improved performance” is for you. This is the crux of the matter - unless you can articulate a specific goal, there is no generally better antenna. (and most goals have non-antenna solutions)
Radio works over a signal range of (say) 60dB. Different antennas have general gain differences of only a few dB from each other. This results in everything working, including the No-tenna, and it being very difficult to even tell if today’s antenna is better than yesterdays, because in practice it is not to a significant amount.
I think that the best antenna thing we could do is to take the effort to put up two antennas with a switch at the operating position. This allows you to choose the antenna that is working best for each contact, and moment to moment.
- Any antenna that is multiple half waves long has lobes and nulls. You don’t really control where they point, and for every band they point in different directions. The lobes are only a few dB strong, but the nulls can be narrow but very deep. If an S2S lies in a particular null, it will be gone
- experiments have shown differential fading (QSB) at HF between similar antennas only a few metres apart can be +/- 5dB i.e. QSB is moving null patterns that are fractions of a wavelength wide.
- incoming waves are polarised, but probably at random, again at some moments the cross-polarisation loss will be big
Plenty of possible combos
- You could just have two similar EFHW’s at (say) 90°, or arranged downslope off different sides of the hill
- You could have a 40/20/15/10m EFHW and a 20/10m EFHW
- You could have two dipoles on different bands at 90° - you would still have RX diversity
- On higher bands (20m up) you could have a vertical antenna which has lower angle of radiation for DX and an EFHW for 40m, and multiband.
- You could have a ferrite rod for 40m (or 60,80) RX only , that lets you null out QRM or strong local chasers. For higher bands RX whips or loops would be options. You are not limited to TX capable antennas.
I am pretty sure that just having live switchable diversity will quite often be worth 6dB in RX signal.
It may let you find out that some antenna or orientation is often working better e.g for DX on15m, which you can never know just trying different antennas on different days.
For making a specific S2S and DX this is probably useful. If you are just making contacts with random chasers it probably doesn’t help, as it really doesn’t matter if a chaser is in the wrong place, you will just work another chaser instead.
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Shouldn’t that be 40, 20, 15 and 10 without a tuner and 60m, 17m with one? That’s what mine does anyway.
Going back to the question. If we’re sticking with simple wires, and not delta loops, moxons etc, then a dipole is less lossy than an EFHW + auto-transformer. However, I’d choose the EFHW 9/10 times simply for ease of use.
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I think it should be good for 15m but on mine the SWR is quite high on 15m (but OK on 10m). Adding a capacitor didn’t make any difference for me.
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I have fiddled endlessly and t’s not possible to get super low SWR on every band, but a good compromise seems to be SWR < 2:1 on each. That should make any rig happy and don;'t forget SWR<>radiation efficiency
Rick
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Hi,
A link dipole will give maybe 1 dB more signal than an EFHW. If you use either in the inverted vee configuration you get some vertical radiation at a useful lobe angle. That’s about as good as it gets in terms of increased performance for a backpacker.
SOTABeams used to sell a range of antennas at a competitive price. I haven’t checked their website lately.
If you want significantly improved signals over a dipole then you need a bigger antenna. That’s how the physics works.
Getting the dipole up 15 or 30 m above the ground helps too but that means increased difficulties in throwing your support cord over a tree.
Don’t fret about a few dB. Variability in propagation will mask most practical differences.
73
Ron
VK3AFW
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An EFHW is the “Swiss army knife” of SOTA. A multiband antenna that you can use quickly with good results. It’s fantastic for on-the-go SOTA where you deploy quickly without needing a tuner. I have made good contacts with my EFHW slung poorly becuase of the summit conditions. It’s not perfect and its a compromise to get the multiband functionality.
If I want DX with improved performance then I take a specific band resonant antenna, like a 1/4wave vertical for 10m, or a dipole for 40m.
Tim
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A flowerpot on 10 m is better than a quarter wave. Fast to deploy and uses minimum real estate. No radials. Works well. Tree branch or squid pole for support. A 20 m one would probably need to be deployed as a sloper or a up and out configuration.
73
Ron
VK3AFW
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