Tag Archives: Vertical

Working 15m band on a 40m vertical antenna

Note: This article discusses the merits of a 3/4 (three quarter wave) vertical -vs- a 1/4 (quarter wave) antenna.

You can build a 40m vertical quarter wave antenna and ground mount it with 16 x 4m radials and operate it at the third harmonic; 21MHz.

Actually, all my experimentation has shown that if you multiply the quarter wave resonance by 3.03, you’ll have the next available usable band. In this case, if you tune a 40m vertical to 7.00Mhz, you’ll have the whole of the 15m band to play with with a centre-point of 21.300Mhz. Oh, and you’ll still have the whole of 40m band under 1.3:1.

Now here’s the controversy:

Most people who read antenna publications or the ARRL handbook believe that if you actually make this antenna, you’re creating a cloud-burner on 15m.

Technically correct (sort of) – but for DX, wrong.

On the surface, the 10m long 40m vertical that’s used on 21.225MHz does indeed look like a cloud burner. Here it is. 15m band in green -vs- a pure quarter-wave in red).

quarter-vs-three-quarter-wavelength-vertical-antenna-plot

(click to expand quarter-wave in red, three-quarter wavelength in green)

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Solarcon Imax 2000 Review 5/8ths Vertical Antenna 10m

Dsc_0002I always fancied a low-angle vertical for 10m band and after doing my research, came across the Solarcon Imax 2000. It was a toss up between this, a Sigma 4 copy or the Sirio 827. The Sigma 4 is now called the Sirio Vector 4000 and I discounted this one because of the size of the radials which seemed excessive for my plot , Same with the Sirio Vector 4000 which is just too tall. Even so, the Sirio Imax 2000 is still 24 feet in length. But read on, it’s actually fairly stealthy for such a tall antenna.

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Salt spray detunes wires on fibreglass antenna poles

I use a lot of fibreglass poles with wires strewn up the sides, normally in a lazy helical fashion so that they don’t flap about too much.

I have great success with these poles as regular readers know however I have noticed that certainly wet weather can detune them ever so slightly. Effectively, they become slightly longer and I fathom that as the fibreglass supports become wet, I am achieving some slight inductance with the water that drips from the surface and gets between the wires and the poles. As soon as they are dry again, the tuning comes back to normal.  Continue reading

3 Element 40m Vertical Parasitic Array (VPA) Vertical Yagi

Essentially, this is a single 1/4 wave vertical antenna with ground radials, complimented by a pair of parasitic verticals; a reflector and a director. It will deliver around 6db of additional gain over a standard vertical with a beamwidth of around 70 degrees. I have built mine pointing 300 degrees so that I can work the US easily at night.

I call this the M0MCX VPA (Vertical Parasitic Array).

 

Hours of planning and modelling with MMANA has finally produced an excellent and extremely economical method of producing gain in one direction, although the front-to-back ratio isn’t superb, it still has some rejection.  Continue reading

Multi-banding 10m long 1/4 wave 40m vertical antenna for 15m band

I’m always curious to discover if a mono-band antenna will work efficiently (or otherwise) on another band. I recall that when I first studied antennas, it was explained that a dipole antenna will be resonant on every third harmonic. That means a dipole for 7.1 MHz should also work on the frequency three times bigger, in other words 21.3 Mhz. Actually, experience tells me that the real resonant frequency will be a little higher.

58 -vs- 14

1/4 wave vertical for 40m band can also be a 5/8th for 15m band

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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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Vertical Antennas for Marine SSB

This article discusses in layman’s terms how an antenna transmits its energy and the various factors that might affect its performance. The target audience is Foundation students and marine sailors since I discuss the positive impact of the sea as a ground, particularly those sailors with fibreglass boats who have vertical antennas mounted up high off the waterline. This debate started in the Yahoo Group, NordhavnDreamers.

Dipoles and Vertical Antennas

ecoflex-15

Coax showing centre-conductor and ground / braid surrounding

The energy from your transmitter is sent via its coaxial cable and connects to the “feedpoint” of your antenna which will radiate electromagnetic energy. Most modern transceivers expect to “see” a 50 ohm load at the point where the coax connects to the transmitter. It’s this reason why coax cable suited for transmissions is more often than not quoted as 50 ohm cable.

Antennas are a little bit like piano strings. If all the piano strings were set at the same tension, the longer strings would play a lower note and the shorter strings will play a higher note.

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40m Quarter Wave Vertical, Cornwall

40m vertical

Quarter Wave Vertical 9.6m in length

I’ve tried many verticals and never had good results APART from this one.

This is a 9.6m long fishing pole and the length of radiator is the same. I fixed 16 x 10m long radials to an insulator that I had lying around. I would have preferred this to have been aluminium but I already had three of these. Most of these bits were salvaged from the three-element vertical array with raised verticals that James and I made back in 2009. Each bolt was bonded together with some copper wire that is out of shot, underneath the insulator and the radials were politely scattered in an approximate radial system on the ground. SWR is 1.0:1 according to my electronic controller on the Acom 2000.

The results have been amazing but I do realise that I had two things on my side; location by the sea and almost no electrical noise. Bliss.

As I write this, I’ve worked 48 DX entities over about 7 hours operating time on 40m. Quite incredible. I’m a convert.

Nested Quarter Wave Vertical Antenna 20m and 10m

20m 10m verticalWith my recent success at building fan dipoles that are more “nested” than “fan”, I saw no reason why I couldn’t put up more than one element on my 20m band vertical to achieve a match on 10m. I ran up a 2.4m length of D10 comms wire up the side of the pole, around 2 inches away from the 20m quarter wave element. After trimming a few centimeters here and there, it tuned it at 1.3:1 SWR and all was well.

To make sure everything really was good, I applied a QRO carrier and watched in amazement as the SWR hovered for a few seconds before moving up and down and finally going off the scale with the Acom shutting down with an alarm (what a great amp that is!).

It took a while to track this down but it turns out the D10 military comms wire had melted at the guying point about half way up the 10m vertical element. I had tensioned it around one of the bolts on the steel three-way guy point to stop it flapping around and it decided to try melt the insulation and finally and weld itself onto it before blowing itself apart. The joys of QRO.

Antenna -v- High Wind

Movie IconWas I QSB this afternoon on PSK31? Probably!

(Can’t get video to play? Right-click and save it to disk first! Don’t ask :)

In the main, we’ve all heard that wind normally beats antennas when it comes to staying up. In case you haven’t ever seen a cheap fishing rod blank in high winds, have a look at this. I call it a 10m vertical, in fact this one is only 8m. The matching is done at the feedpoint with an SG230 and 9 raised radials. It’s a temporary antenna. I’m just testing it out for fun. The 12m beats this by a fair margin on the 40m band.Anyway, enjoy the little film!

By the way, don’t be fooled by the helically wound look. It is hardly that. Here’s a real helically wound vertical from a couple of years ago – and this one does tune on the 40m band without help from an SG230. It is directly fed with coax:

73

Callum.

12m SpiderBeam Vertical Pole Antenna

I’ve really been impressed this weekend over the quality of 160m SSB operators who I found were courtious, patient and keen to accept my call. I’ve done single-band entries before on 40m where the tight frequency allocation and numbers of operators mean that there’s a pretty agressive tension in the air – not so 160m. There seemed to be space enough for the big runners to hold a frequency and enough of them to allow the casual Search and Pounce operator to have a couple of hours fun from time to time.

12m SpiderBeam Pole

Regular readers of this site know that although I’m a keen contest operator, I love building and testing antennas. This weekend allowed me to build something a little different to squeeze in a 160m vertical into my back garden where I only have 10m x 15m to play with (in old money, that’s only 30 x 50 feet).

Pictures tell a thousand words so I won’t go into the heavy details other than I used up the full 12m SpiderBeam pole and put up 8 radials ranging in size from 6 meters through to 12 meters (telephone wire, spare from an old reel). The Feedpoint was 2 meters off the deck and the radials were parallel to the ground. I fed it at the feedpoint with an SG-230 powered by a car battery housed in the shed. 30 meters of low-loss, double-shielded Westflex coax fed the tuner.

My only trouble was that after a few hours, the pole started to telescope into itself with the strong wind which required me to take it all down and hose-clamp (jubilee clip) each section after using liberal amounts of plastic tape so that I wouldn’t damage the fibreglass. SpiderBeam do a clamp-set with small rubber shields and if you are thinking of getting one of these, do buy the little clamp set, it’ll make your life easier. Even then, one of the sections moved a few inches in the night. It’s settled now – but you can see the vertical telephone wire that I used as the antenna has become slightly loose.

Results were quite encouraging and with only three or four ventures onto 160, fitting in dinner, bedtimes and some family TV, I scored 51 QSOs with the USA being the biggest potential DX. I didn’t work them though. My footprint covered the near Atlantic islands (Madeira etc), North Africa through East Mediteranean and up around European Russia and Finland. I genuinley didn’t believe that such a small antenna would work that well particularly at only 100w. I think getting all the RF into the antenna instead of wasting power heating coax may be the key here – and it’s the SG-230 that takes the blame for this :)

Final relaxed score was 51 QSOs, 24 Countries for 6,144 points.

REF Contest: Not content with one contest this weekend, I also entered the REF contest. Conditions were terrible though. I’ve had much bigger runs into France on 40m but not this weekend. It kept me out of trouble but certainly nothing to write home about. 20m was off the score card because I could rarely find any propagation into France on 20m – the same on the higher bands too.

It did give me a chance to use the vertical though for general purpose DX and occassional tests with James (M3YOM) who had also put up a similar antenna this weekend – also using an SG-230! For me, some mixed results although the vertical normally won the competition barring 80m where the higher levels of radiation inter-UK suited the full-wave NVIS loop better.

I’m left with one question: Why did the vertical work on 160m locally – but not on 80m locally where the loop was required? There’s some propagation going on here that I don’t understand. More experiments are required.

Overall though, a great experiement though.

Cheers and beers.

Callum.

 

Helically wound 40m vertical

Helically Wound 40m verticalChris (G0EYO) kindly modelled my 40 meter vertical with loading coil (http://www.m0mcx.co.uk/?p=44) and mentioned that he felt the take off angle may be higher than I would like it.. He suggested experimenting with a helically wound vertical. Chris recalls a team event last year where they needed to get on 40m fast so a fishing pole and about 10 meters of wire were produced along with 2 elevated radials. The problem was that the fishing pole was only about 7 meters long. The team simply wound the 10 meters of wire on to the fishing pole and hit the TUNE button on the rig to swallow up any mismatch.

I tried the same experiment with my 8 meter fishing pole and 10.6 meters of wire. Why 10.6 meters? Simply because I cut the wire a bit long intentionally. Using 4 elevated radials, I found the resonant 1:1 frequency with a near 50 ohm match was 7.7 Mhz. Way above my requirement however the SWR bandwidth curve was very strange with a flat 2:1 SWR all the way from 7.2 Mhz right up to 7.6 Mhz. Indeed, the TUNE button easily swallowed the incorrect size of this antenna for the whole of the 40m band. I needed to make this longer though so I could run high power in a comfortable manner.

Stripping off the 10.6 length, I found a 100 meter roll of 6 core telephone wire and chopped 15 meters off it. I wound this on to the fishing pole which gave me 6.8 Mhz. A couple of attempts later and about 50cms of wire short, the vertical tuned in to 7.05 Mhz with a very large bandwidth, certainly better than the loading coil version.

Later in the evening I heard VE1KF managing a European pile up from his QTH in Nova Scotia. My vertical broke the pile in one shout. He emailed me later, “Your signal was a nice strong 59“. Thanks for the report Brent.

I give a thumbs up to this antenna; I believe I am getting a lower angle of radiation. It’s the best 40 meter vertical I’ve made yet but remember – these only work from about 1,000 miles upwards. If you want lots of QSOs, you’ll need a dipole or a loop to compliment this.

More pics: http://www.m0mcx.co.uk/gallery/index.php?/category/40

Postscript: I recommend using a 1:1 choke balun on this design to stop the feedline radiating and to ensure that all the RF goes where it should. See here http://www.hamuniverse.com/balun.html for some regular designs.

73, Callum.

20 meter quarter-wave vertical antenna experiment

Not content with attempting to understand and build 40 and 80 meter verticals, I’ve decided to build a 20 meter version tonight. This has 4 x sloping radials at 45 degrees with a feedpojnt up at about 7 meters in the air. On receive, it’s actually pretty good; only for extremely weak or barely readable signals is it beaten by the 40m loop or my attic mounted half-sized G5RV.

For the record, it performed straight out the box with dimensions of a whisker under 5 meters for both radiator and radials.

Picture below shows typical far-field plot for a quarter-wave vertical.

vertical-gain-at-30-degrees

Dedicated 80m Vertical

80 meter loaded vertical

I didn’t document fully last weekend that my 40m vertical experiment gave me a rather good match on 3.8Mhz. This gave me the idea of building a better 80m vertical this weekend by loading up both the vertical – and the radials. As I type this as I discover that first time up, I’ve achieved a resonance (of sorts) at 3.456 Mhz however, I’m not getting 50 ohms. The SWR is at best just under 2:1. I have reduced the legs of the radials a bit because of the loading coils (which all have 68 turns on my favourite 40mm plumbers pipe). I shall now adjust only the vertical coil. I know I should in theory adjust all the coils to keep them in unison however, the actual length of the radials is not precisely known; only that they are ‘about’ 9 meters plus a loading coil – and in any case I can just shorten the radials for fine tuning.

Here’s the resonant coil adjustment chart for the vertical coil:

  • 68 turns: 3.456 Mhz
  • 67 turns: 3.470 Mhz
  • 63 turns: 3.535 Mhz
  • 59 turns: 3.600 Mhz
  • 55 turns: 3.690 Mhz (1:1 SWR dead)
  • 54 turns: 3.691 Mhz (I tightened up the radials which had an adverse effect so that the resonant frequency hardly moved)
  • 52 turns: 3.740 Mhz (SWR rising a whisker now)

I finished on 53 turns in the end. I’ve started keeping a couple of turns or more spare, never cutting off all the ‘dead ones’ as I take them off so I can wind them back on if I overshoot. My ‘best’ spot frequency is now 3.715 at 1:1 SWR with a 2:1 SWR curve starting at 3.6 and going all the way beyond 3.8. In fact, 3.8 has an SWR less than 1.5:1.