QRPpppppppppppppppppppppppp...

Yesterday, with a lot of non-radio things to catch up on, I set the 14MHz vertical delta loop to work at the lowest power I've yet tried.

My WSPRlite units only go down to 5 milliwatts.  I used a 10dB attenuator to achieve 0.5 milliwatts (500 microwatts).

5mW out into a 10dB attenuator.

I thought I was doing quite well to be achieving 1676km to Italy during the afternoon.  As greyline approached,  I was very happy to be heard by EA8BFK at 2864km, well above the detection limit at -22dB.

I left the transmitter going overnight, and when I checked this morning, I was amazed to see 0.5 milliwatts had confidently crossed the Atlantic, to make -22dB at WA2TP!  This is a kilometres-per-Watt equivalent of 10,588,000 km!

Reception reports for my 500 microwatt 14MHz WSPR transmissions, 11:52UT - 06:34UT 22-23/9/2020

At these QRPpppp levels, the receiver has to be in a quiet environment.  So this experiment really does sort out the 'men from the boys' in terms of who really is operating an optimum receive station, and who isn't.  

Sample of reception reports.  Note: reported power is limited by WSPRlite parameters.  Actual power was 0.0005W (i.e. 10dB lower than reported)

 

At an achieved -22dB from home with this power level, there are 12dB 'spare'.  That indicates a power output of 32 microwatts would theoretically just be detectable across the Atlantic with my vertical delta.

But from the beach, there is an environmental gain of about 10dB available.  So the theoretical power output limit from this kind of omnidirectional antenna for detection in the US, ignoring any propagation enhancements, is about 4 microwatts. 

Inevitably, I will have to try this experiment at a west-facing beach this week, to see what happens there.  At least I have a well-defined time window, between 19 and 22UT, where propagation is strongest, to limit my standing around in the cold and the dark, unless the magnetic field changes!