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There is a warning on the QRP labs site NOT to use the BPFilters on LPF Power amp clean up duty......
Timothy E. Fidler : Engineer BE Mech(1) Auckland , NDT specialist AINDT UT /RT3 , MT2 CB #2885,
Telephone Whangarei 022 691 8405
----- Original Message -----
Sent:Sun, 27 Jan 2019 13:29:29 -0800
Subject:Re: [BITX20] Spurs/Harmonics fixes for v4 based on v5 board design?
I'm hoping that we can find a cheap way to measure for spurs. I built the 7mhz band pass filter based on the QRP labs kits one and put it on the antenna for testing. I think it cleaned up some of the spurs/harmonics but it's still showing one when transmitting at 7.15MHZ at about 28MHZ range that is only -30db on the scope FFT - since its only 8bit ADC not sure if it's accurate or not.
I wish I knew if the scope FFT amplitude was accurate. I love the frequency range on it, can view huge swaths of spectrum