Tag Archives: multi-band

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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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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MegaLoop Antenna

XXT Meage LoopI’m currently writing an article outlining the characteristics of the Mega Loop antenna we use for Dorridge Scouts. If you would like a preview of this white-paper, please let me know.

The XXT Mega Loop is the name given for the application of a horizontally mounted delta-loop that has known gain dependant on wavelength size and height above ground.

At quarter wavelength above ground and above, Mega-Loops start exhibiting gain that is proportional to its wavelength and height. A whole series of articles is currently being written by the author, however for the time being, these few articles may help you determine how we operate the Mega-Loop at Dorridge Scout Group HQ.

Firing supports over trees:

The 160m Loop

GB1DSG Special Event Mega Loop Project

Aidan M6TTT

Picture shows Aidan, M6TTT running his first pile-up from the Hut. First class Aidan, you really got the swing of this on Sunday. Fabulous effort.

We put nearly 800 QSOs (contacts) in the log and there are so many highlights, I can’t begin to mention them all. My personal highlight was working VK3FT at lunchtime today with a land-line quality copy on the 20 meter band. Keith spotted us which probably accounted for flurry of VK stations immediately afterwards from Australia. Thanks Keith.

We got spotted 25 times over the weekend which is certainly our personal record. Thanks to those stations that helped us maintain the pile up!

As usual, we used the MegaLoop (delta-loop) antenna, see this page for details:

Cheers all!

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.