WSPRlite and the need for a band pass filter

Set the WSPRlite for use in the 80m band  at a 100 mw transmit level and connected it up to a Spectrum Analyzer.



 Sotabeams recommends a Low Pass Filter when using the device on the lower bands.     Its always good practice to limit the amount of interference you transmit.  

Looking at the intermod levels compared to the desired carrier seemed high at first but when you look at the levels they are pretty low.

The above statement is not correct ,  Richard from Sotabeams commented on Youtube " Thanks Ron. However, the outputs are harmonics - not intermod products. The waveform is a square-wave. Low pass filter required! 73 Richard G3CWI "

Freq                                                       O/P dbm     watts
80m  3.592 MHz  ( the desired freq )   21.8 dbm  = 151 mw
40m  7.0386 MHz                                   2.8 dbm  =     2 mw          
30m  10.8 MHz (outside the ham freq) 10.5 dbm  =   11mw
20m  14.4 MHz                                         4 dbm =   2.5mw
17m  18.0 MHz  (outside the ham freq) -1.5dbm = 0.7 mw