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Antenna Performance Measurements


#21

Hi Barry, Heinz gave a loss per 7 metres - that would make a loss of about 1.62 for 30m (100ft) as we normally see it. so at 14MHz (rather than 50MHz) this would give 1.4 to 1.5dB (per 100ft/30m) and is about the same as you say.

Here are the comparison of the proposed lengths - 12m

and 5m

(calculator used is at http://www.qsl.net/co8tw/Coax_Calculator.htm)


#22

Part of me thinks that most people would use a vertical with a short run of feeder compared to the Inv V. The setup allows you to reduce the coax loss because you don’t need it. So the different lengths of feeder may actually be more representative of reality.

As long as we know the setups then I don’t think it matters.

My $0.02 worth.


#23

But that is not logical; you can actually use the vertical with 2m feeder (possibly less) - you can not do this with the dipole so the extra 6m is an essential part of the dipole setup.

Actually I am more concerned at the idiosyncratic ground conditions which I think make the test valid only for this hill.
73,
Rod


#24

Mulling this over on the walk home, a few more thoughts -

If it were me conducting this experiment, starting from my limited knowledge, I would interpret the result as showing the difference between these two specific antennas, on these two specific locations, with these ground conditions (wet / dry / frozen). Also with this dipole orientation, and with the antennas at these heights above ground.

On top of that, I would have to define what I mean by “better”. For me, my objective is to achieve at least 4 contacts as quickly as possible. As Ed implies higher up the thread, this means getting signal to an area populated by Radio Amateurs, who are likely to be awake at the time.

Others with greater knowledge might well be able to discount some variables, or at least quantify their significance.

The experiment should produce a lot of data for individuals to interpret, I think it will raise a few more questions too :o)

73
Adrian
G4AZS


#25

Richard,

I think that’s an excellent experiment and I will be interested to see the results.

Fwiw I have compared similar antennas but without the measurement system provided by the WSPR network, reporting system and analysis by the dx explorer site.

Andrew VK1AD and I set up a dipole and a vertical configured very similarly to your proposal. Though the dipole was straight. That was when we activate Bowning Hill, vk2/st-042, just under 800m ASL. The 20m band was used and we asked (mainly European stations worked) for signal reports when switching between the two antennas using the same radio. As I recall it the antennas gave similar results with some variations for vk stations at different directions from the EU orientation. We had oriented the dipole to favour the LP/SP directions for Europe.

However I think using WSPR will allow the signals to be compared using common components and software that is intended to measure signal levels, rather than the somewhat subjective audibility reports from ears backed up by signal meters of unknown quality but known inaccuracy, amongst varying QRM.

There are many other comparisons that would be worth making. But let’s see how this one goes.

73 Andrew VK1DA VK2UH


#26

Hi Richard,

Please do not lump modelling in with “unsupported opinion”. They are like cheese and chalk.

We must have passed the centennial of the first horizontal vs vertical field evaluations. Even in 1914 radiation patterns were computed to compare with field testing, albeit slowly and by someone of professorial rank.

You could improve the comparison of your proposal by comparing the averaged signal strengths as reported by the (same) receiving stations. I assume both WSPR transmitters are running in the same time slots.

73
Ron
VK3AFW

Post edited by author


#27

Hej Adran,

the linked pdf states the wspr data will be accessible to ham public. So anybody can tell by the data, time, and direction which of the antennae fits their personal needs. It would be sure better to get data from different locations/summits to make the measurements more objective. But hey, you can’t complain unless you go out and measure for yourself. :wink:

Love Kant.

Ahoi
Pom


#28

I usually love to explain why something won’t work :), however this looks like a really good plan.

I support the idea of having different cable lengths for the two antennas as it’s a closer representation of what the typical arrangement will be for an activator. Daytime is also typical for SOTA activations.

We need to keep in mind that the results won’t necessarily apply to the 7MHz band (or lower), as it will be much much harder to keep the same antenna height in wavelengths - the challenge grows exponentially.

Really glad we now have the tools for experiments like these.

Razvan.


#29

Thank you all for your thoughts. I will redraft the methodology and respond to the various constructive criticisms next week. In the meantime I am happy to receive more comments on the thread here.


#30

While that could work with Einstein’s cats two Schrödinger’s cats so close together might lead to problems since the observer becomes entangled with one or both of the dead or alive cats.

73, Jaakko AC1BB/OH7BF


#31

Did someone say Schrödinger?

Heisenberg and Schrödinger were driving along the freeway/autobahn/motorway and Heisenberg was speeding along. A traffic cop saw them and chased and stopped them.

Cop: "Do you know how fast you were going?"
Heisenberg: "No officer."
Cop: "You were doing 100mph!"
Heisenberg: "Well that’s brilliant, now were completely lost."
Cop: "Uh? Anyway what have you got in the boot/trunk?"
Schrödinger: "There’s a cat in there."
Cop: “Show me…” Heisenberg pulls the remote release, cop goes around the back.
Cop: [Shouting from the back of the car] "Hey! Hey! This cat is dead!"
Schrödinger: [Sighs] “Well it is now!”


#32

Hi Richard,

I will also be interested on your results. Thanks for the tests. I use to do tests but carrying & installing two antennas in a summit sometimes is difficult…

Could I ask you to add in your PDF info about orientation of the Dipole Legs? (i.e. North-South deployment?) We know in advance that Dipole will have some sort of Directivity, so it does worth to add info on the direction of the legs to take that into account.

Thanks and I’ll try to receive your signals from here (if I can read 200 mw!).
73 de Ignacio


#33

…it is already there!


#34

Oh yes! Figure 3, the dipole is beaming Northwest… Thanks


#35

With limited elevation AGL (which is good, because it mirrors actual use), I think you’ll find that soil composition and moisture content will impact performance.

One thing which has become clear to me is that summits are different from each other. I frequently read things such as, “there are always rocks I can use” or “I can always push a stake into the ground” or “with the slope, the antenna ‘sees’ itself as if it were atop a tower”. Some summits are solid granite; some have a rich loam soil; some have arid, sandy soil; some are sharp peaks; some are more like elevated fields.

You’ll get results which apply to the summit where you test. Agreed that testing on different summits is a different test, but I’ll bet you’ll find more difference between those antennas on summits where the soil composition is relevant. Of course, you could always prove me wrong by testing them on very different summits!


#36

I have compiled the comments and have made responses thus:

Criticism: the hill chosen may favour one antenna over another due to its shape [G4AZS, M0JLA]
Comment: accepted
Mitigation: new hill selected (Gun SP-013).


Criticism: the antennas may interact [G8TMV]
Comment: accepted.
Mitigation: measure mutual coupling on site. Ensure that it is less than -40dB (happy to accept considered opinion on other figures).


Criticism: carry out the test twice with antenna positions reversed to remove position bias [M0LEP]
Comment: accepted (in respect of original site).
Mitigation: new site should remove the need for a repeat. I may carry out another test for position bias.


Criticism: the dipole legs should be inline [G4AFI]
Comment: the antenna configuration is chosen to represent what is typically in use for SOTA.
Mitigation: none.


Criticism: an inverted vee is not omni-directional [N1EU]
Comment: accepted. It will be orientated to be broadside on to the DX location most likely to provide useful data (USA).
Mitigation: none.


Criticism: the length of co-ax should be the same for both antennas [DD5LP]
Comment: the systems have been chosen to be representative of real SOTA systems.
Mitigation: none.


Criticism: the experiment should include close in performance too [DD5LP]
Comment: that’s another experiment, for another time. The data from this experiment will be available for alternative analysis.
Mitigation: none.


Criticism: the results will only be valid for these antennas on this hill [G4AZS]
Comment: Quite possibly; however I can only do one thing at a time.
Mitigation: none.


Criticism: modelling is better than opinion and anecdote [VK3AFW]
Comment: accepted. However, modelling needs to be backed up by practical experiment to ensure its validity. It seems to be widely accepted (here at least) that modelling alone was no more able to give an unambiguous answer in this case than other methods.
Mitigation: none.


Criticism: the results will not apply to 7 MHz [YO9IRF]
Comment: accepted. They probably don’t even apply universally to 14 MHz.
Mitigation: none.


Criticism: we should be using cats [OH7BF]
Comment: getting radio amateurs to agree on anything is like herding cats.
Mitigation: none.


Criticism: soil composition and moisture content will impact performance [K4KPK]
Comment: accepted. It will be one of several variables that will be impossible to account for in a single experiment. However, the soil composition and moisture content will be similar for each antenna.
Mitigation: none.

I will now amend my method statement.


#37

Looks like a good plan to me. And you have the tools. Yes, there are minor little variables involved, but no activation is without them. So, I do not see where any of them are significant. The only thing I would suggest would to be in your setup configuration for the two WSPRlites - you would want them to transmit in alternating time periods.


#38

Why alternating time periods? Why not same time, different frequencies?


#39

Seemed to me that if they both transmitted at the same moment, even if they were on different 20 meter frequencies, that there could be some interaction . . . . Just a thought . . . . Maybe not a meaningful thought . . . But if I were going to sit out there all day while this runs, I guess I would try to do everything possible to insure that nothing abnormal affected the results. Jody - K3JZD


#40

I’d be curious to know how this turned out. Has the test happened? Is there data available?