Tag Archives: horizontal

Bidirectional switchable 40m wire yagi

I switched on the other evening and heard a very quiet DX caller on 7.142. It was YC0LOU from Indonesia and I could only pick up parts of his call. He called and called and had no takers. In fairness, he was extremely quiet but as the sun was gradually moving around the sky, he finally became audible and it was worth giving him a shout. 400w off my inverted V at 7m height got his attention but I needed a few blasts for him to get my call right. I put him on the cluster and he had a pile up.

Now, the point is, had I had more gain, I’d have not only heard him better, but he’d have heard me quicker too.

So I could add more height to my Inverted V but the difference between 7m and 10m isn’t actually that much at 5 degrees off the horizon – not even a db. Hardly worth writing home about.

40m-wire-yagi-drawingAnyway, this was the QSO that made me sit up and take stock of what I could do. I was seriously considering phased verticals for DX when I thought up the idea of having a switchable wire yagi. Either firing East or firing West.

Like me, you may already have an inverted V dipole up for 40m, all you need to is build another one about a quarterwave in front – or behind your existing dipole but out of a single wire. You don’t need to feed this with coax, it’s a parasitic element, like a 2 element yagi.

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Marine SSB Antenna Vertical or Horizontal

The diagrams included in this article were modelled with a program called MMANA. If you are inclined to give this a go, its a free download and I have produced training films on YouTube

NOTE: I have intentionally modelled the vertical antenna with a bad ground to replicate the findings of some fibreglass yacht owners who run a 15 to 20 foot copper ground strap to Dynaplates. I have modelled the horizontal antennas over sea-water.

This article follows my paper on raised feedpoint vertical SSB antennas for fibreglass boats. In this article, I look at an alternative; a horizontal dipole antenna which I will call an offset doublet and a Mk2 version, with a vertical component at the rear. We will continue to use the ATU matching device (often supplied by Icom) which will remove all the hassle of mono-banding and tuning. Marine SSB relies on a number of frequencies so an ATU to dial out the mismatch is vital.

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80m vertical -vs- 80m horizontal loop

Vertical vs Horizontal:

Overview: The first thing that I noticed was that during daylight hours, the vertical was utterly hopeless. Inter-G signals were virtually unreadable, to the point I thought it wasn’t working. Indeed, being daylight, I couldn’t hear a thing, just noise. Switching my NVIS loop in to circuit brought the band to life with usual weird discussions of carrot growth and weather. As nightfall fell, the vertical started performing but nowhere near the performance of the loop. By 22:00 UTC, the Russian and nearby European stations started coming in stronger, but again sounded better on the loop and it didn’t seem to matter what antenna I used to transmit on either. One German noted on comparison tests absolutely no difference on TX.


I called for RP3PRP on the loop (he was loud) and he had some problems receiving me so I switched to the vertical and we exchanged reports and my confidence rose. Again with 9A7KM, I started the exchange with the loop because that’s where he sounded so good but flipped to the vertical to complete. Confidence grew higher. Then UP0L in Khasakstan for a 3,500 mile hop again on the vertical. But this isn’t the whole story. Don’t think the vertical performed better on TX than the loop everytime – this isn’t the case. This particular vertical is one heck of a compromise; remember, only about one ninth wavelength and only three meters above the ground.

My loop on the other hand is a proven high performance antenna that’s got a history of DX to the Far East and North and South America. After a couple of hours and 48 QSOs across 20 countries, I realised that for 90% of the QSOs that you make on 80m, an inverted V, a regular dipole or perhaps a delta loop (like mine) at around 30 feet will be fabulous – and you’ll have the advantage of being able to have a QSO in your own country. Occasionally, having the flexibility of switching the vertical in gives you an added interest but it’s hardly worth the effort. A 4-square would be a different story though, and for the uninitiated: a 4-square is 4 x ¼ wave antennas phased in a square, quarter wavelength apart that ‘pushes’ a lobe of RF (db gain) in a specific direction at the push of a button. However it’s hardly an event antennal, more suited to permanent installs.

For me though, I don’t think this test was completely conclusive. I’d like to build a full-size quarter wave with full-sized raised radial set to complete the test with a feedpoint at 5 or 6 meters above ground: in other words, doubling the size of this little twig and maybe I can aim at building it for this year’s NFD. I have a feeling that it was the loaded radials that was restricting my efficiency, not the loading coil in the driven element. My experience of a 40 meter quarter wave gives me some confidence in this arena but I’m also wary of the different characteristics of 80 meters which maybe much more suited to higher dipoles.

There was though one small advantage that I haven’t documented, and that’s the use of a vertical as a dedicated QRM receive antenna. I scored many points by finding distance stations between strong UK stations. I can reduce UK stations by around 40 db by switching in the vertical, whilst at the same time keeping the target station clear in my headphones.

In conclusion, verticals for 20 meters and above may well be good performers and I’ll certainly have a bash at a 20 meter version of this shortly but for 40 meters and below, be clear about what they’ll do for you. I do not recommend them as your primary antenna unless of course you are very restricted on space – and even then, there are shortened alternatives that can be squeezed into small plots.

Shortened / loaded 40 meter dipole for attics

This morning, I removed from the loft, a pair of nested dipoles for 40 and 20 meters fed with one coax feeder. The 40 meter dipole was loaded with some coils so that I could fit it in the attic.

It gave me 40, 20 and 15 with a push because although a 40 meter dipole should give you a resonant 15 meter antenna, in this case – with the coils for 40 – it mucked the maths up and caused the ATU some trouble. On 40m, it worked a treat.

If anyone is interested in making up the “shorty forty”, you may find my experience of interest: Each coil was made from 3 meters of hard drawn BT downlead, coiled around a PVC plumbers pipe of around 25mm diameter and about 30 turns or thereabouts. The actual spec from the dipole centre was as follows:

  • Dipole centre to coil: 3.7 meters
  • Coil to end of dipole leg: 3.3 meters
  • = 7 meters each leg + length of the coil

I replaced the nest was replaced by a half-size G5RV in a “lazy” inverted V configuration, tucked up in the rafters. Good for running a second radio and it gets me on 10m as well as the WARC bands.

Incidentally, when I was testing this original dipole, I started off with 8 meters for each leg and ran it through the MFJ analyser. It was resonant on 6.66 Mhz. An old favorite pirate band that some people may remember. Adding the coils raised the renonant freq from 6.6 to 8.5, so cutting a meter off each side to get the whole thing working for the amateur bands was necessary.

So there you have it, a 45 foot long 40m band dipole.