KX4AZ WSPR with 10 milliwatt

Last week I received a very nice e-mail from Bruce KX4AZ. He searched the net with "WSPR 10 milliwatt" and found the page on "WSPR with 10 milliwatt" on my PA1B website. hi.

Bruce KX4AZ is a operator that makes very interesting WSPR spots with just 10 milliwatt.

Believe it or not. A WSPR station with 10 mW will be spotted, but ONLY when the propagation is very good. Please study the diagrams below, to convince your self.

Lowest Possible Power diagram
To show the propagation, I developed the Lowest Possible Power diagram. You can immediately see how good or how lousy the propagation is, for each individual spot.
The better the propagation, the lower the Lowest Possible Power.

2019-04-19 I visited the WSPR old database and collected some interesting spots.

Time slot 1 
In the time slot of  17:46 UTC ND7M spotted 7 stations.
4 stations with 5 W, 1 station with 1 W, W6CLB with 100 mW and Bruce KX4AZ with 10 mW.
Luckily for Bruce, the propagation from the stations with 5 W and 1 W, to ND7M was not that good, so Bruce's signal was not over shouted by the 1 W and 5 W signals. Something that can easily happen, even with a power of 100 mW.
In the first diagram Bruce was spotted by ND7M with a SNR of -29 dB. It's the spot in yellow, on the line of -29 dB and the line of 10 mW. So in this time slot Bruce needed the full 10 mW. Hi.
In this time slot the best propagation is shown by the spot of W6CLB with 100 mW and a SNR of  -15 dB. This spot has a Lowest Possible Power of 5 mW. Thus about 3 dB better than the spot of Bruce.

KX4AZ with 10 milliwatt spotted by ND7M over 3100 km

Time slot 2

The second diagram shows the next spot of KX4AZ by ND7M. 

In this time slot the signals of W6CLB with 100 mW has a SNR of -12 dB.

The signal of KX4AZ has a SNR of -22 dB. please notice that both spots, show the same propagation, which is very good. The Lowest Possible Power of both stations is 2 mW. The signal of Bruce is even about 7 dB stronger, than in the first time slot.

KX4AZ with 10 milliwatt spotted by ND7M over 3100 km

PA0K spotted by W4HOD

Here is an other analysis of a spot made by Paul PA0K on February 1^st 2019. He was spotted by W4HOD over 7200 km with a SNR of -23 dB. This spot reveals, that the propagation, between Paul's station and W4HOD, was not good, at that moment. But never the less, Paul's signal was received, with a bit of luck, as we will see.

Spots sorted by propagation
The table shows all the stations, that were received by W4HOD in Alabama in the time slot of 13:12 UTC. I have sorted the spots by propagation, using the Lowest Possible Power (LPP). The lower the Lowest Possible Power, the better the propagation. The propagation to W4HOD was good, or even very good, for the first 9 stations in the table. This are the stations that have been spotted with a LPP of 50 milliwatt or less.

PA0K
The propagation from Paul's QTH to W4HOD was poor with a LPP of 500 mW.

PA1OSF
W4HOD also received PA1OSF over a distance of  7200 km from The Netherlands. PA1OSF was received with a LPP of 20 mW. The propagation from PA1OSF was 17 dB better than from PA0K. The distance between PA0K and PA1OSF is 71 km (44 mi). The difference can be caused by propagation, antenna direction and the antenna.

Spots received by W4HOD

The propagation between VE3KAE and W4HOD shows the best propagation with a LPP (lowest possible power) of 0.5 mW. Luckely for Paul, VE3KAE used 100 mW. Believe it or not, if VE3KAE had used 5 W, in stead of 100 mW, this signal would have used a large part of the dynamic range of the receiver of W4HOD and Paul's signal would probably not have been spotted.

Frequencies
I noticed that W4HOD received twice the number of spots compared other stations. In an analysis of frequencies that were used, I saw, that W4HOD can receive two signals a few Hz apart. This suggests that there are more than one WSPR receiver or detector at W4HOD.

Dynamics
The dynamic range of the SNR is +1 -(-26) = 27 dB.
The dynamic range in LPP is 1000/0.5 =2000, which is 33 dB.

PA0K spotted by EU2AAH

Here is a further analysis of spots made by Paul PA0K on February 1^st 2019. The propagation was not that good. But Paul's signal was earsplitting into Belarus. He was spotted by EU2AAH over 1500 km with a SNR of -3 dB. This spot reveals, that the propagation, between Paul's station and EU2AAH, was very good, at that moment.

Lowest Possible Power diagram
I developed the Lowest Possible Power diagram, to compare spots, that are made with different power. The Lowest Possible Power diagram shows instantly, how good the propagation is.
A spot is placed on the diagonal line of the power, that is used by the transmitting station. The height of the spot in the diagram is determined by the SNR of that spot. You can read the Lowest Possible Power of a spot, on the horizontal axis.
The better the propagation, the lower the value of the Lowest Possible Power.

Spots by EU2AAH
This diagram shows all stations, that were spotted by EU2AAH in the time slot of 13:52 UTC. It can be seen instantly that 3 station were received with good propagation and 2 with very good propagation. The letter gives the DXCC of the spot.
Paul's signal (PA0K) was the strongest signal, with a SNR of -3 dB. The arrow to the horizontal axis points to a  Lowest Possible Power of 5 milliwatt. The LPP of 5 mW is in the area of  very good propagation.
The propagation between F6KOP (F in the diagram) and EU2AAH is even better, with a LPP (lowest possible power) of 2 mW.

Lowest Possible Power diagram of spots received by EU2AAH

The line of 10 milliwatt
The dashed line in the LPP diagram is the diagonal line for a power of 10 milliwatt. PA0K and F6KOP could also be spotted if they would use a power of 10 milliwatt. If PA0K would reduce from 2 Watt to 10 milliwatt, his signal would be received with a SNR of -26 dB. F6KOP would be received with a SNR of -22 dB with a power of 10 milliwatt.

Table of spots received by EU2AAH

This is the table, that I used to draw the LPP diagram.