Mini-bog experiment.

Three years ago, I wrote a post about an odd phenomenon that happens just down the hill from my house, where radio signals at commercial VHF are strangely interrupted as one passes over an underground acid mine drainage channel.

This evening, it was sunny and warm, so I decided to take a walk up onto the old copper mine, directly above the underground stream.

The mini-bog site on the copper mine hill.  I didn't know the wet ground existed until today!

Well, the ground here is very mineralised, and it has a better and slightly higher view of the sea than my house, even though it's only about half a kilometre away.  In practice, I will never really be able to figure out which element of the environment makes any difference, if any.  But it's a nice comparison, all the same.

Despite this being an almost universally rocky area, I found an unusual area which was like a mini-peat bog, and consequently quite wet.  As well as providing a rare place to screw my antenna mount into the ground easily, such a site was likely to be excellent ground.

Parys Mountain disused copper mine.  Test tonight from upper centre left, not far from the main road. 

 

I ran WSPR at 14MHz using a 1/4 wave vertical, two elevated radials and my FT818, principally for RX-only.  At home, as usual, I was using a vertical delta loop, typically having 3dB more 'design' gain than the 1/4 wave.

Results were pretty amazing.  The median enhancement of the signal, taking differences in 'design' gain into account, was 9dB.  The maximum enhancement, to the signal from DP0POL lying near Svalbard (an essentially all-sea path), was an astounding +16dB, which is the kind of enhancement I might find when the antenna is actually at the seawater's edge.  

This calls to mind, and surely confirms as correct, the comments about the Fresnel zone for radiation angles <1 degree being "pushed [far] out to sea" that Les Moxon discusses with some excitement in his enduringly-good book, HF Antennas for All Locations.  With some elevation as well, that Fresnel zone for ultra-low angles may well be pushed further out again.

Line of underground drainage channel (yellow).  Blue circle centre was test site location.

Map displayed at Parys Mountain, confirming drainage channel route (top left, crossing B5111 road).

The minimum enhancement was +4.5dB, though that was to a TA station lying to the east, with the hill intervening.  It's not really worth taking a lot of notice of that particular result, other than to note it is still significantly stronger than the delta, which has a clear view to the east.

A total of 5 stations heard on the mini-bog were not heard at all from home.  All but one were good DX stations, being AA6FT, R0AGL, VE2DPF and K7GCB.  M0GUC, heard at a median -27dB on the mini-bog, was also missed by the delta at home.  

Taking AA6FT as an example, heard at a median -19.5dB on the mini-bog, the enhancement must have been around 14dB for it not to be registered at the detection threshhold (about -34dB) at home.  R0AGL's results also suggest an almost identical implied enhancement.

DP0POL's reception of my single 1W test signal, compared to others at around the time, adjusted for power output, can be seen as being very favourable - at least 7dB better than any other UK station, of which there are anyway only two (I was 14dB stronger than the other UK station):

The other good DX station who heard my 1W was ND7M.  Again, hardly any other UK stations making it around that time, with my 1W being, when adjusted for the different power output, a whopping 17dB better than GI3VAF:

-18dB from my 1W to ND7M, compared to just -28dB from 5W from GI3VAF.

This test again shows just how poor a comfortable, at-home station can be, even with a proven, good quality antenna.  The difference is not down to any RFI, because I've already proven that's not the case with a comparison of noise at home and seaside, where there was no difference.

Acid mine water found within Parys Mountain. It's red due to a very high level of dissolved iron, kept in solution by a pH of 1 or less (at above ~pH 5, iron falls out of solution as a red floc).

 

These kinds of amazing enhancements are at or beyond what we would achieve with a world-class tower-and-Yagi system when operated at a typical, non-coastal environment.  The environments that provide them really should receive more study.  I plan to do just that in the future. 

Even more importantly, the majority who have poor domestic radio prospects can easily get out into the outdoors and enjoy extremely effective amateur radio with only very modest equipment and low power; an enhancement of 14dB takes a typical QRP output of 5W to an effective 125W!