G4ILO Whispering with 20 mW and 1 mW

This is an other analysis of the data collected from the
WSPR database for spots of Julian G4ILO.

Julian transmitted with a power of 1 mW and 20 mW.

The table shows, that the spots that were made with 1 mW, 

were about 10 dB weaker than the spots made with 20 mW

The table shows a selection stations that received spots made with both 20 mW and 1 mW

To compare spots over different distances, I use the 

Calculated electrical field strength, E, in microVolt per meter.

For details see the WSPR Propagation Analysis page of this Blog.

The lower the electrical field strength the better the propagation.

A power ratio of 10 means 10 dB. 

Please notice the the value for E is given in Volt/m, so a Voltage ratio of 10 means 20 dB. 

Which is indicated at the top of the table.

A Voltage ratio of 10 is a ratio of 100 in power.

The table shows stations that received the signals, that were transmitted with 1 mW and 20 mW.

Notice the difference in field strength in spots made with 1 mW or 20 mW.

The difference in field strength between the spots of 1 mW and 20 mW is about two steps in this table.
This is about 10 dB.

This is no surprise because, the difference in power between 1 mW and 20 mW 

is  10 log (20 / 1) = 13 dB.

The differences in propagation are huge. 

The field strength of the spots made with 20 mW, received by ON7KO over 600 km, 

show a value of 0,3 microV/m to 0,03 microVolt/m. 

The ratio in voltage is 10 and the ratio in power is 100, which is 20 dB. Wow. 

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)