Using a 5W Linear Amplifier with a 200mW WSPR Beacon
I’m a big fan of WSPR for many reasons, normally operating a Sotabeams WSPRLite beacon TX on 40m at 200mW 24x7x365 and also RX using my Elecraft KX3 connected to a Windows 10 laptop running WSPR v2.12 as much as I can using call sign M0VGA - software crashes depending (sorry K1JT)… both using individual OCFD wire antennas from Aerial-51, locator IO93fx.
This experiment was to see how an increase in power from 200mW to 5W would increase the distance of spots received. WSPR is a very efficient protocol but 200mW isn’t a lot of RF power with a modest antenna setup - 5W represents a very substantial increase in the WSPR world given WSPR is all about weak signals.
I purchased a 5W linear amp from Hong Kong via eBay for £30 and a 20dB SMA attenuator for the input (thanks to Richard at Sotabeams for the advice). The quality might not be amazing but it’s good value for the occasional experiment. I configured the beacon with my spare call sign M6WFM using 40m for 24h for this experiment.
The linear amp got quite hot even under no TX load despite a fairly substantial heat sink so I sat the amp on top of a USB powered fan to keep it cool. This reduced the peak case temperature from 48°C to 31°C during the test period.
When using only 200mW power my usual spot pattern is a large part of Europe on 40m, with occasional North America spots and very exceptional spots from more exotic locations. I was very pleased to see that with 5W RF power I was able to be spotted many times in North America, South America and Australia over a 24h period.
There’s more experimentation to do of course, but interesting to see how the RF power increase made such a difference.
Comments welcome :)
6th September 2017