WSPR: More Environmental Evidence Emerges

A long time ago, I wrote about (forgive the dead image links!) my experience, during only one QSO, of a comparison between my vertical delta loop and another operator's 3-element SteppIR in south Wales.

I didn't expect many to take much notice of that little exercise and indeed, as expected, one person was sufficiently aggrieved to comment on it being of no consequence.

Since then, things have moved on significantly.  WSPR provides a wholly human-free means of testing antennas (unless you're one of the very few who transmit more power than advertised!).  WSPRlite then came along and gave us accurate (within about +/- 11%) QRP outputs, with most choosing to transmit 200mW.

Last night, I received an email from an operator about 37 miles from me, living within 1 mile of the Irish Sea.  Like me, he has a fairly quick drop-off to the coast, although that land is, unlike mine, densely developed, albeit mostly with fairly low domestic buildings.  He wanted to know a bit more about WSPR SNR reports.  I gladly assisted.

Unlike me, though, the operator in question has a very fine multiband 2-element quad at 12m up.  Interestingly, he was comparing his antenna with another station fairly close by, running a three-element Yagi.  Both directional antennas were beaming the US at about 315 degrees.

Now, my antenna for 14MHz is and always has been a vertical delta loop, with a perfect match through a 6:1 balun. A lot of people, especially Americans, claim the antenna is 'only' a simple wire and is 'too low' to be very effective, and 'certainly' can't match a multi-element beam.

This certainty probably makes them feel good.  But they are very wrong.  They are ignoring, above all, the environment from which the antenna works.  Ground conditions given by an old copper mine, a clear, elevated and undeveloped horizon in all directions, and the sea being about 1.5 miles way at closest, all add together to give great performance.

Now I had the details of the quad in use at GW0ADC, I could see how well my delta could do.  The time of day and propagation conditions meant that almost all signals being received were from the US (largely eliminating any performance 'boosts' that may otherwise come from the omnidirectional nature of my antenna).

Firstly, here's the HFTA terrain plot for both GW0ADC (blue) and myself (red).  The terrain is measured on a digitised Ordnance Survey map, and then manually entered into HFTA:

Here's the plot of overall distances achieved by both over a part of the day:

Not bad, eh?

How about simultaneous spots and reported SNR?  Surely, my delta must do really badly?

Can you see that difference at the bottom left?  A 0.28dB difference - i.e. essentially no difference at all - between my single element (plus its ground image) vertical delta loop and a full-blown 2-element quad at 12m height.  No human bias involved!

To be fair, these spots include the very few that were coming in from the EU, away from the beaming direction for the quad.  If we eliminate these by limiting the spots to those from beyond 3400km, the quad does better, beating my omnidirectional delta by 2dB.  That's a small improvement in SNR given the complexity and expense of a 2-ele quad on a tower over a simple fishing pole vertical delta wire!  At about 4000km, the difference was only about 1.5dB, but it increased to the same 2dB beyond about 5000km.

 

The comparison with the 3-element Yagi was even better.  First, the terrain plot, blue being GW3TMP, red being me:

Next, the system gain figures (again, blue is GW3TMP, red is mine):

And finally, the resultant simultaneous spot strengths for spots beyond 3400km (again, to eliminate all 'off-beam' spots, limiting them to only those from the US): 

Simultaneous spots for GW3TMP (3-ele Yagi) and MW1CFN (vertical delta loop), limited to US-only spots.

The poorer terrain for GW3TMP's Yagi yields a nearly 4dB advantage for my delta loop, even though it's omnidirectional.  This example clearly shows the importance of very low angle take-offs.  So much for the old addage that a vertical antenna simply 'radiates equally poorly in all directions'!

So, what's that I'm saying?  That a single element vertical delta loop can be almost as good as a 2-element quad at 12m high, and better than a 3-element Yagi also at 12m up?  Yes!

Am I crazy?  No!  The results speak for themselves.  The reason why my delta is nearly matching or beating the performance of much 'manlier' antennas is that the environment is better, at least in that beam direction. 

If you are still shaking your head and tutting, let's return to the computed system gains (i.e. antenna plus ground), for the 2-ele quad at 12m and a dipole (HFTA can't compute vertical antennas) at 6m (the equivalent mean height for my vertical delta loop, which may be a valid comparator antenna):

System gains at two different locations.  2-ele quad (blue), vs vertical delta loop (red)

Now my claims are supported by HFTA evidence.  The crucial area is the very low angle region.  Here, the total system gain (i.e. antenna plus ground gain), despite the very different antenna types, is only 1dB different.  Obviously, there is a very much bigger difference for higher angles, but those are normally less important for longer DX.  The story is the same with the Yagi comparison.

Unfortunately, because of HFTA's limitations in relation to not computing vertical antennas, we can't be sure this is the whole story.  But the logic - and results - seem to hold up pretty well using a horizontal dipole at equivalent effective height. 

The quad's pattern looks like this model from MMANA-GAL modelling software.  Notice how, at 1 degree elevation, the gain is minus 8.5dBi, though the sloping ground at GW0ADC may tip this pattern over clockwise, to the right slightly. 

Yagi elevation pattern.

My delta looks a bit more like the plot below, partly due to sloping ground, and partly due to high conductivity ground.  The pattern has been confirmed with an RF meter here, where peak gain is at, or even very slightly below the horizontal.  Notice that the peak gain at the horizon is plus 7.4dBi:

Vertical delta loop pattern is more like that for perfect ground at this QTH.

And as a last piece of evidence that the environment is indeed better at my location (red) than at GW0ADC (blue), here are two modelled dipoles, both at 12m at each location, with a focus on the 300-315 degree beam heading. In fact, this shows a very slightly better low angle gain at GW0ADC, which may again suggest the US stations receiving us at the time were coming in at angles of about 3 degrees, or above:

Theoretical dipoles at 12m at each location.  Red is my QTH, blue is GW0ADC.

The story is, again, the same (and more marked) for theoretical dipoles at GW3TMP - the Yagi QTH (blue) - versus my QTH (red).  For The Yagi, though, the bit of high ground at about 10,000 feet distance has a significant impact on system gain; except for a small blip, it stays below mine until the mid-twenties degrees, where it is of little DX use.

So the WSPR results first showed something amazing was happening with a simple antenna.  Then the outcome is supported by terrain modelling.  Anybody continuing to argue that there is 'no way' this can be true is simply falling victim to the thing I have strenuously removed from all my work: human bias and prejudice.  I do keep repeating it, but Les Moxon certainly didn't fail to recognise the importance of antenna environment, and he was no idiot.  His colleague, G2JKF, once told me that Moxon always sought a hillside location when moving home.

Presumably, if the quad and Yagi could be moved here, they would beat my delta at that point.  In fact, running the HFTA model again shows the quad would have about 2.5dB more total gain if located here.  Not that a huge multiband 2-ele quad would survive our terrible winds, anyway.

So there we go.  Yet more objective evidence that the environment is really very important to antenna performance.  It doesn't feature very much, if ever, in antenna articles I read.  But it very much should.  Indeed, the failure to discuss antenna environment might be the last remaining human bias in antenna testing, because very few authors have such a good environment, and may never have had the chance to evaluate a better one - or even realise they exist.  Worse, they may be wilfully ignoring the environment because they can't change their lot!