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Wire pyramid for SOTA activation


#1

Hi SOTA Fans!

Why not a wire pyramid for SOTA avtivation?

It needs no more than a 7m or longer fishing pole, a few meters of string, 4 spikes, 40m of #15 to #18 wire plus about 10 meters of light-weight coaxial cable, e.g. RG-58/u. The 4 sloping lines have double role as those are not only radiating but also fastening the holder fishing rod. In possession of some experience a single person too can erect it in a few minutes.

As far as it can be judged reading Karl Rothelmer’s Antenna Book, it will work fine at 7 and 14 MHz, but not at 10,1 and 18,1 MHz. As it is a full wave wire at 40m, the main SOTA band, it provides somewhat more signal compared to a half wave dipole. Being a closed loop, it is less sensitive for static charging, thus it provides more silent reception. It has a circular radiation pattern and this is an advantage for activators especially in the LX-HB9 strip. Finally it provides a low radiation beam elevation angle that may be advantageous for inter-continental connections. That is, there are more pros than cons as it provides a solid performance… at least according to technical papers.

Has anybody out of you collected practical experiences with a wire pyramid during SOTA activation?

73: Joska, HA5CW


#2

In reply to HA5CW:

Its an interesting antenna. At the design frequency it seems to be two inverted v dipoles 180 degrees out of phase, similiar to a pair of crossed dipoles but end fed instead of using a phasing line.

Nigel. G6SFP.


#3

In reply to G6SFP:

This isn’t the same as the G3ENI pyramid antenna that was in RadCom TT in 2003 or so is it? The TT article was for 60m working but the designed can be scaled.

Andy
MM0FMF


#4

In reply to MM0FMF:

I dont know Andy. I found an 80m version here:

http://f6arc.free.fr/pages/12_1.html

Nigel. G6SFP.


#5

In reply to G6SFP:

Looks very, very similar.

Andy
MM0FMF


#6

In reply to HA5CW:

It needs no more than a 7m or longer fishing pole, a few meters of
string, 4 spikes, 40m of #15 to #18 wire plus about 10 meters of
light-weight coaxial cable, e.g. RG-58/u. The 4 sloping lines have

In this case the bottom of the two triangles is touching the ground and *NEC will calculate high losses which will probably lead to an overall gain much less than for a dipole far off the ground. I know this since I am using triangular loop antenna 40 - 17 m on the ground with ATU and have been modeling it quite a lot. Still did not bother to use the dipole yet, since my antenna seems to work too, is compact and has some safety for statics or lightning. The interesting thing is that on an Alpine summit you are actually on top of some kind of pyramid already :slight_smile:

73, Jaakko OH7BF/F5VGL


#7

In reply to F5VGL:

Dear Jaakko,

The ground loss is an important point, thanks for noting it. Karl Rothelmer suggests 2-3 m (that is 0.025…0.035 WL) spacing for a 80m pyramid. I supposed that the same value (expressed in WL) will work at 40m as well.

I was talking about a 7m or ¤¤¤LONGER¤¤¤ rod. Considering 7m long edges (n.b.: 6x7=42m wire is resonant at around 7 MHz) and 8m pyramid tip height; the horisontal lines will occur at about 1m above the ground. Maybe, you are right and this is insufficient. Than use not 7 but 8m long rod! It will provide already twice as much, that is about 2m space (0.05WL) spacing from the ground! That should be sufficient.

As the test of the pie is eating, the testing of an antenna theory is building it, working with it, comparing it to other antennas, that is ask not only standard 599, but exact signal reports. Switching between antennas, asking another report. This can be done either in your back-yard, or out in the nearby field, that is you need not climb any hill or mountain carrying batteries, RIG, etc.

Has anybody played with this? And this is, what my question was about!

73: Joska


#8

In reply to HA5CW:

Hi Joska,

You are right about the pyramid trigonometry. From mechanical engineering point of view I can see one possible problem though. The tension on the wires and guy lines will result in vertical force to the top part of the rod and this has tendency to bend the tube. Thus it might be good idea to start with something stronger than a simple fishing rod and maybe also add other guy lines. Good luck with you experiments.

73, Jaakko OH7BF/F5VGL


#9

In reply to HA5CW:
Hallo dear Joska ! Yes i played with this antenne , some years ago in my garden with very good results , it is not the best antenne for DXing but the signals from EU and near DX stations were good , i received mostly 579 up to 599 from stations in a distance between 600 - 2000 kilometres . I used a middle mast from 8 meters high . Unfortunatately i have no more fotos of this antenna
Best regards and iw ish you good results when you will testing this interest antenna . Thats it what ham radio is !
73 de Ben DL2DXA


#10

In reply to DL2DXA: Hello Ben!

Thanks, this is, what I was interested in!

You are absolutely right, the more tension you apply in order to avoid the wires hang loose, the more vertical load the fishing rod will have to bear, thus it will band, or accidentally break. This is the reason why I was talking about relatively thin (no more that 1,0…1,5 mm diameter, possibly non-insulated or enamelled) wires. It is prudent to forget about the tip section of a telescopic fishing rod and use only the 5 mm of larger diameter sections. This means, in practice, that you need to buy at least one meter longer one, than you actually need to erect your piramid.

Did you notice any degradation in performance due to terrain features (e.g. you, sitting close to the piradid! :slight_smile: ), or due non-horisontal ground surface? Did you use 1/4 WL 75 ohm feed-line to match it to 50 Ohm? (Someone wrote about 90 Ohms feed-point impedance.) How did it perform at the 1st harmonic, that is at 14 MHz? How much the 1:1,5 SWR bandwidth was? Had you been able to use it both in CW (7.032) and SSB (e.g. 7.118 MHz)? Did you need any antenna tuner at all?

I think, I will test this design somewhere at a nearby peak providing a reasonable size hozisontal glade free of terrain features and tall vegetation. :slight_smile:

Have a pleasant week-end and make many SOTA QSOs!

73: Joska, HA5CW