Analysis of G3XBM's 40m WSPR spots with 5 mW

G3XBM left WSPR running with 5 mW on 40m for 24 hours.
Roger concluded that his signal was in the noise most  of the time.
He also concluded that he would need 2 W.
http://g3xbm-qrp.blogspot.nl/2014/01/40m-5mw-summary.html
The analysis below shows that the conditions changed dramaticly after the 7 spots with 5 mW.

The header of the table shows the Calculated  Lowest Possible Power in mW (Click for info), 
which is calculated from the used power (Pwr Sent  in mW) and the SNR.

The better the propagation, higher the SNR and

the lower the Calculated Lowest Possible Power will be.

The analysis
9 UTC gives the spots that were made in the hour from 9:00 till 9:59 utc.

This first line shows, that the power that was needed for the spots was 1 W down to 2 mW

In this hour, half of the spots that were made with 2 W could be made with 100 mW.

The white circles indicate the power with which half of the spots could be made.

The lower the power needed, the better the propagation.

From 9 utc till 14 utc on the 18th there are 11 spots with a calculated lowest possible power of 5 mW or less. So it was possible to make spots with 5 mW.

WSPR with 5 mW
From 14 utc Roger reduces further to 5 mW and over 24 hours only 7 spots were made, shown in the yellow coloured part of the table. In the red part of the table there are no spots since the power that was used is 5 mW. In the red part I show the receiving stations and their SNR.

Back to 2 W
You would expect more spots, since the 24 hours before showed many more spots that could have been made with 5 mW. But the conditions changed dramaticly.
The last part of the table shows spots that were made with 2 W.
At 20 utc on the 20th at least 500 mW is needed.
And at 5 utc and 7 utc spots could have been made made 5mW

G4ILO Whispering with 20mW and 1 mW

Julian G4ILO did an interesting experiment with WSPR. 
He used a power of 20 mW and 1 mW and was heard over large distances.
I made a table of the spots with both 1 mW and 20 mW.
I left out the few spots that were made with 50 mW.

The table below shows an interesting phenomena.
When 20 mW is used, the  calculated lowest possible power is 20 mW or less.
When 1 mW is used the calculated possible power is 1 mW or less.

The Lowest Possible Power is calculated from the used power and the SNR.

The SNR for a solid copy with WSPR is -29 dB.
When a signal is received with a SNR of -19 dB, this signal is 10 dB stronger, 
so the power could be 10 dB reduced and still be solid copy, but then with a SNR of -29 dB.
The Lowest Possible Power is 20/10 = 2 mW 
22 Spots were made with a Lowest Possible Power of 2 mW.

The tables below show the distance, the receiving station and the power that was used.

WSPR Propagation Analysis

Changes in propagation give huge changes in signal strength. 

WSPR has a SNR that can act as an S-meter. 

But if you want to compare WSPR spots, you also have to take 

into account the output power of the transmitter. 

WSPR Propagation Analysis

I use the calculated lowest possible power

in milliwatt of each WSPR spot, when

• the spots are all made over the same distance
• the spots are made with different power.

The lower the calculated lowest possible power, 
the better the propagation.

Solid copy

The SNR of a WSPR signal can be as low as -33 dB.

But a WSPR signal that is received with a SNR of -29 dB will be a solid copy.

Calculated Lowest Possible Power
A signal with an SNR of -19 dB is 10 dB stronger,  can be reduced with 10 dB
(1/10th of the power) and still be solid copy, but then also with a SNR of -29 dB.

The better the propagation, the stronger the signal and the higher the SNR will be.

The more the power can be reduced and the lower the Lowest Possible Power will be.

But the frequency must be clear, to actually receive a signal with the Lowest Possible Power.

G4ILO Whispering with 20mW

Yesterday Julian G4ILO wrote on his interesting Blog about his advantures with WSPR with low power:

Many people who operate the weak signal mode WSPR use too much power. 
If you don't use very low power (QRPp) you'll never find out what this mode is capable of. 
So to remind myself I thought I'd do some whispering on 10m using 20mW of power. 
It's easy to use low power with the Elecraft K3 as the power level is adjustable in 0.01 watt increments. 

The power of 20 mW that julian used to WSPR can be compared with 400 mW in CW. (13 dB --> 20x)

Today I visited the WSPR database to make the following analysis.
In each spot I calculated the lowest power what could be used, to be received with a SNR of -29 dB.
The stronger the signal, the lower the lowest possible power.
The stations that received the strongest signals are ON7KO (600 km), LA9JO 1900 km) and ND6M (6600 km)

Beeldenlaan

Het lange pad.

Moet je eens kijken, 

het is nu vijf voor vier. 

T'is het maar tien minuten lopen

van daar naar hier.

Gisteren ben ik met de eFiets naar Rhijnauwen geweest om te wandelen.
Het was heerlijk zonnig weer.
Aan het eind van de Beeldenlaan van Oud Amelisweerd naar de Vossengatsedijk, realiseerde ik mij dat ik over dat pad slechts tien minuten gedaan had.

Aanvulling:
De foto heb ik genomen na mijn bezoek aan de tentoonstelling van Armando
in Oud Amelisweerd vorig jaar in oktober. Presentatie in Prezi.
Halverwege de Beeldenlaan had ik het zo warm, dat ik mijn jas heb uitgedaan.