Yesterday, I looked at data gathered from the inland direction (i.e. signals coming from mainland Europe and somewhat beyond), and those coming in over the sea from North and South America.
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| Sea and coastal ground - all good for RF! Image (C) MW1CFN |
The median difference for signals coming in from the rear (land) direction was +3dB. For the sea path signals, it was a median of +9.5dB. So the sea itself yields +6.5dB additional 'gain'.
The run of data capture could ideally have been longer, and at some point, I will make that effort.
But the emerging picture is that the seawater-saturated sand underneath my antenna at the coast is acting as we would expect from theory. Being a near-perfect RF reflector, the sand-water mix almost eliminates ground losses and creates a similarly near-perfect second virtual element in the ground that yields this doubling of RF power received.
I wonder if the quieter location at the coast is also a factor? Would that account for that 3dB advantage in signals coming from the land/rear?
ReplyDeleteAre all of your measurements based on receive only? I wonder if you did transmit tests as well. Will the receive and transmit advantage readings in dB match up?
It's a fair question, and one that needs a proper investigation. Any suggestions for a simple way of measuring RF noise at HF? I think the Lelantos software from RSGB measures the noise floor as part of VDSL noise assessment, but I'm not sure of the detail.
DeleteHome has always been RF-quiet, but it does have electrical circuits around it, and local voltage transmission lines nearby.
On the other hand, there are two large solar PV farms not too far away from the beach location.
Oh, and yes, I have done lots of TX experiments. RX only is just the latest activity, spurred on by the need to develop a lightweight, low power portable receiver. TX confirms the typically 10dB enhancement seaward, but often much greater (up to 27dB seen so far on very rare occasions). I will have to look at past results to remind me of TX in the landward direction. It all sounds simple, but the data analysis quickly overwhelms you when you try to be as accurate as possible!
DeleteI've been wondering about this and I think the easiest way to do it would be something like a SDRPlay receiver. As far as I know, the signal levels in it are in dBm and you could look at the respective noise floors.
ReplyDeleteI agree, John. I have the RSP1a all ready to go in the backpack, and can take both direct measurements and, via WSJT-X, take .wav recordings to run through various software for analysis back home. Bit windy for the next 36 hours, but I'm sure I will need some exercise by then...
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