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Antenna Performance Measurements


#1

An earlier lengthy discussion here of whether a vertical or horizontal antenna is better on a hilltop seemed to get no-where, being based on:

  • anecdotal information;
  • unsupported opinion;
  • modelling.

No-one seemed to want to actually do any tests to measure anything.

This year I am keen to at least make a start towards an answer. As a result I have drafted an outline methodology. Before actually doing anything, I would be grateful for comments on why it won’t work so that I can refine the method such that at least a few might accept any results.

A PDF can be downloaded here.


#2

That appears to be an invalid pdf

Colin

Ah, he’s fixed it - works now


#3

I can read it.
(Firefox on Linux)
73,
Rod


#4

Yes, it opens correctly for me in Chrome on Windows…

I like the experiment, and the results will be interesting.

The only point that occurs to me is that the “red” area seems to be closer to the escarpment than the blue.

I don’t know whether that would make any difference, but if it might, then perhaps the experiment could be repeated with the antenna locations reversed…

73
Adrian


#5

A very interesting plan, Richard. I wonder if the rather sharp edged ground profile gives a serious skew to the results for the dipole. It seems to me that a flattish area of fairly uniform ground would provide a more repeatable situation. I notice that Adrian makes a similar point; I think the vertical is compensated for by the radials.

73,
Rod


#6

How close are the antennas? I suspect the answer is “too close” the elevated radials on the vertical are going to affect the Inverted V.

Colin


#7

You could try to balance effects of the different locations by performing two tests, the second with the antennas in the other locations, but you’d need two locations suitable for both antennas…


#8

Personally would have thought what ever you can throw up in the location your at depends on what you can put up.
I run a 40m 1/4w vert and if possible and the location allows a 1/2w inverted L to which requires more room to which some locations just won;t allow. Both get me out nicely even with small output of 10w.

Love to go up summits with a 40m loop but bit much. Hence the simple antennas i use for portables.

Karl


#9

Please quantify with justification.


#10

I think I would prefer it if the dipole legs were inline and you found an alternative method to support the pole. Perhaps this is the way you normally erect an inverted V on a summit; maybe I am unusual in erecting mine inline as much as possible? What will be the inverted V angle?

73 Andrew G4AFI


#11

The inv Vee pattern is going to favor receivers in a broadside direction versus the end-fire direction. This is going to complicate comparative data analysis. I’ve modeled the in Vee antenna for 20M and the end-fire direction will be 5-10dB down from broadside, depending on the takeoff angle from the summit.

Barry N1EU


#12

I can’t tell from your drawings how far apart they are. But I was always taught that having resonant wires (i.e. your 1/4 wave radials and vertical) within one wavelength of a dipole would cause interaction, which will occur in both senses (each affecting the other) of course.

Colin


#13

Thanks for that Colin (albeit rather anecdotal). I think I will perform a mutual coupling measurement between the antennas before starting the experiment.


#14

Good idea. I’ve been thinking recently about pairs of phased verticals and four-squares, although they are closer together (typically a 1/4 wave) there is obviously a lot of interaction, since that is the whole point of doing it.

Colin


#15

It depends on the summit Karl, I have used a 40m horizontal loop on VK2/HU-093 Mt. Elliot. It worked very well until some kid ran his bike into one of the masts!

Ed.


#16

Hi Richard,
Can I request that you use the same length of coax on both antennas, so that the loss from the coax (albeit minimal) is the same in both cases. Your PDF states you will use 5m on the vertical and 12m on the Inverted-V.

Ed.


#17

I too looked at that; the extra length is essential for the dipole as the feedpoint is at the top of the mast instead of the bottom.
73,
Rod


#18

7m of RG-174 has a loss of 0.38dB @ 50MHz, the lowest frequency for which I have data. Somebody might have loss data @ 14MHz which will be negligible (for amateurs) or could be easily accommodated for in final field-strength results (for purists).

RG-174 Cable data

73 Heinz, OE5EEP


#19

I think that number may be off Heinz, and it’s more like 1.5dB. Here’s the loss chart I find for 100ft/30m of RG174:

73, Barry N1EU


#20

Yes understood the Inverted-V needs 12m - but theres no reason that the vertical can’t have 12m on it as well - to make a fair set-up. As I said the difference in loss will be minimal however why “fix” the data afterwards when you can simply use equal lengths of cable on both antennas.

An additional question - with DXPlorer.net - are measurement possible, “Closer-in” (i.e. NVIS) as well as from DX receivers? Using WSPR, I would expect it is - one question I would love to have answered is which antenna is better for contacts closer in - My belief is that the dipole will be better, as the vertical has a lower angle of radiation but it’d be good to have that proved please Richard.

Ed.