Careful how you test antennas!

I was out well before sunrise at the east-facing beach this morning, during a flat-calm, clearing sky.

This mission was to test out a single turn magnetic loop of 10mm microbore copper, which was recycled from a successful 'figure-of-eight' project a couple of years ago.

The loop is only 2.5m in circumference, or a little under 800mm in diameter.  It's fed with a 'pseudo gamma match', via a 4:1 balun.

Mounting things securely in the field is one of the biggest headaches with this antenna type.  I found a timber stand blew down without guy ropes.  Ropes are not ideal in the field, as they take time, space and represent a trip hazard for other beach-goers.

So, last night, I drilled two holes in the L-section steel I have, which was made initially for a 10m fishing pole.  With bolts and a couple of wing nuts, the permanently-fixed loop, capacitor and balun just slip onto the steel really quickly.  Tuning with my homebrew remote system proved very quick, stable and gave a perfect match for 14MHz:

L-section steel driven into the ground makes a sturdy support.

Now, when it comes to analysing the 14MHz WSPR results, this antenna is tough going!  Why?  Because it is both directional and has a relatively narrow beam, notably with vertical radiation (i.e. to the left and right of the loop above).  So simply looking up every station isn't going to work - especially when, as in late November, the path from places like VK and ZL is variably long and/or short path, which serves to complexify things a lot!

Here's a pretty rubbish video I made with the current meter showing how the radiation changes quite quickly with position.  Note also that, perhaps surprisingly at the beach, that the near-field radiation pattern is not especially low.  Singal is peak when the needle is at the bottom of the meter in this video:

 

And for completeness, here's the radiation perpendicular to the plane of the loop, which is purely horizontally polarised:

Overall, I wasn't able to find non-long path DX stations that were within the reasonable line of fire of the vertical beam.  That said, I did find that this tiny HF antenna at the beach reached ZL1ROT at -22dB, exactly matching the signal achieved by my vertical delta loop back home (which has a much better aspect to the antipodean point, mid-Atlantic, which is not a favoured direction for today's beach location).

RZ3DVP was reasonably close to the peak beam in the vertical plane.  The magloop was 3.5dB weaker than the vertical delta loop at home, despite having the sea to help it.  The exact-same difference was seen with OH3FR, and pretty much the same (-4dB) for RX-only JMBNSWED in Sweden.

I'm now starting to wonder whether the loop might actually work better if it is closer to the ground, than about 1.5m above it?

In fact, my inveterate antipodean eccentric counterpart, VK3YE, got to this question a long time ago, and seems to answer it quite conclusively, albeit by moving the damned loop far too quickly for us to get a good grip on what's happening.  In his video, it seems the received signal is better at around waist height than over his head or much closer to the ground, although it's a question as to whether he is receiving with vertical or horizontal radiation when he holds the loop vertically - both radiation types are in effect in that orientation.

Inevitably, I will have to test this out again, perhaps from my west-facing coast, where the long path is clear and assisted by the sea.