10m FT8 shoot-out: Delta vs. Magloop.

For some time, when needed, I've used my 14MHz vertical delta on its first harmonic, for 28MHz operation.  With an excellent match for both bands, this cut down the need for yet another, separate antenna for 10m.  Feed to the delta is by 300 Ohm twin to a 6:1 balun, then direct via ~4m coax to the rig, no matching box then necessary.

I was well aware that the harmonic use meant a less-than-ideal radiation pattern.  Less than ideal, but by no means 'useless'.  

The 14MHz vertical delta used on 28MHz for this test.  Apex height ~8m.

 

Here's the predicted pattern for the 14MHz vertical loop used at 28MHz, using real ground values (remember, I am on the flanks of an old copper mine).  Lots of horizontally polarised cloud warming, but also useful, vertically polarised lobes at low angles:

MMANA-GAL prediction for 14MHz vertical delta at 28MHz.

 

In any event, you can look at a wire loop and come round to thinking that, as it's so big, it must do pretty well, because of its capture area and excellent matching.  Surely, it must be better than a set of four 10mm copper rings, just 45cm in diameter and 2m above ground?  There are still plenty of angry white men who shout, loudly, that magloops are just 'dummy loads'.

4-loop array, with ovoid primary loop.  External diameter of loop = 45cm.

But is that kind of conclusion correct?  The radiation pattern for the loop to keep in mind is this:

Much better, vertically polarised pattern at low angles for the magloop, with moderate cloud warming also.  24MHz, single turn prediction.

I set up my parallel, 4-magloop array at about 2m base height, using a traditional primary loop arrangement, rather than a pseudo-gamma match this time.  I found the primary loop, fitted between the second and third secondary loops, yielded a quicker matching solution, and that pulling it into an oval, with a fair amount lying outside the secondary loops, brought fine matching control, eventually giving 1:1.

 

I did need to use different rigs to gather the data.  The delta used a FT-450, and the magloop a FT-818.  Both systems used ZLP interfaces and the latest WSJT-X.

I used FT8 to gather data quickly, and from a wider range of stations than WSPR at 10m typically provides.  On WSPR at the moment, most stations are in Germany, with only a small number elsewhere.

Whilst FT8 does indeed provide lots of quick data, processing it can require good spreadsheet skills, or hours with paper and pencil to time-match 15 minutes of captures.  I can tell you I regretted using the latter approach!

The summary is that the magloop was indeed generally better than the wire delta.  Indeed, there were notable, modest-distance DX stations (see last few plots at the end of this post) that the magloop heard repeatedly and consistently, whilst the delta either did not hear them at all, or only heard them occasionally.  4LQL and UA6XES were important DX cases in point.

A note on the plots: the x-axis denotes just the sequential number of simultaneous spots.  I haven't noted the time, because it's not really useful here, and the data analysis was already very hard-going!  The test was between 09:25 and 09:43UT on 31/05/2021.

Let's start with very close stations - 2I0UIR, which is close enough (roughly 200km) to be ground (actually, mostly sea) wave, plus a bit of Es-scattering, possibly:

2I0UIR received FT8 spots, 28MHz.  Median delta = -9.5dB; median magloop = -13dB

Moving out 1127km to Germany, DO5SB provides the first useful comparison, and an indication of better performance by the magloop array:

DO5SB. Median delta = -5db; median magloop = -2.5dB.

The greater number of spots from DO2SBS (1255km), convincingly confirms the magloop's better performance:

DO2SBS: median delta = +0.5dB; median magloop = +15.5dB

Moving 897km to the south, to EA7ALL, the magloop returns a slightly weaker response from this direction's horizontal polarisation:

EA7ALL: median delta = -4dB; median magloop = -7dB.

Italy, the bread-and-butter 'first hop' for British stations, with IO2LXV not too different in both antennas, at 1318km:

IO2LXV: median delta = +6dB; median magloop = +7dB.

Moving back to central Europe, SP9UPH at 1005km provides a good result for the magloop again:

SP9UPH: median delta = +3dB; median magloop = +9dB.

Now on to two Slovenian stations, first S50XX at 1528km...

S50XX: median delta: -9dB; median magloop = -1dB.

 

...and S56GD at 1554km:

S56GD: median delta = -6dB; median magloop = +3dB.

Now some modest DX, from RK4FF at 3213km, where the delta is better on average:

RK3FF: median delta = +6dB; median magloop = +1dB.

Same story for R3PK, at 2672km.  The dramatic change for the delta at spot 4, as in other cases, indicates a shift in arrival angle and/or polarisation for the signal in question:

R3PK: median delta = -7dB; median magloop = -10dB.

Now for the really interesting results, from reasonably good distances.  First, 4LQL at roughly 3700km, which was heard consistently, and at good strength with the magloop, but missed repeatedly by the delta (I don't know why the spreadsheet coloured this differently!):

4LQL.  No medians, as it's clear the delta isn't hearing the station most of the time!

Then UA6XES, at 3635km:

UA6XES.  Again, the delta almost always didn't hear him.

And finally, the same story with E73DN, at a closer 1966km: