QRP can get around

One of the interesting things you can calulate from WSPR spots recorded on the WSPRnet web sites is the number of kilometers that each milli watt of power from your transmitter covers.
Using my WSPRLite Classic Transmitter running 200 milli watts into an OCF dipole I made the following contacts.

12-Feb-2018 at 12:28 UTC to K9AN at EN50wc total kilometers 17660.

A calculation to K9AN shows that for each 1 milliwatt of signal the Transmitter covers a distance 88.30 kilometers.

9-Feb-2018 at 20.50 UTC to F5OIH at JN06ci total kilometers 14419

A calculation to F5OIH shows that for each 1 milliwatt of signal the Transmitter covers a distance 72.09 kilometers.

9-Feb-2018 at 22.32 UTC to DJ3KJ at JO30fu total kilometers 14022

A calculation to DJ3KJ shows that for each 1 milliwatt of signal the Transmitter covers a distance 70.11 kilometers.

Since I have been playing with WPR over the last 5 years I have used a maximum of 5 watts with a Yaesu FT-450D on a long wire antenna with a MFJ Tuner. Then I switched to a Flex 1500 and
initially ran it with an output of 2 watts, but then reduced it to 1 watt with almost the same contact results. For further experiments on WSPR I set up a Raspberry Pi running 10 milli watts
through a home made LPF (Low Pass Fillter) which while I got some local spots was not very effective. To this Raspberry Pi I purchased from the Tucson Amateur Radio group one of there
Ticson Amateur Packet Radio 20M WSPR Amplifer and filter Board to fit the Raspberry Pi. This certainly improved my Spots on the WSPRnet web site, but I had one small problem the output
would drift between 1 and 5 hz during the transmittion. Tried heat sink with blower fan made almost no difference. Tried different models of the Raspberry Pi from Pi-1B a Pi-2B and a Pi-3B,
of all the Pi-2b had a little less drift but after some months trying every thing I could think of in both the mechanical setup, as well as changes to the software, I took it of air.

The one thing I did find that the Raspberry Pi did very well was decode WSPR signals, using WSJTX software. Using this software with either a audio feed from a communication receiver or with
a audio feed from my Flex 1500 produce extremely good results. The same Setup also works well to decode Digital SSTV using the QSSTV Version 9.1 software.

Digital transmittion modes have improved the effectiveness of low power transmittions (QRP) to the point where 5 watts or less can get contacts world wide. I will continue to play with more
low power systems just to see what else can achieved.