Problems exposed on uBITx sans filters

Warren WA8TOD, who has now relocated his µBITx to the top shelf (of abandoned projects), but he has provided us with a series of shots of the output of the µBITx on different bands, with no LPF filters in place.  These show the raw product coming out of the µBITx and put in full view the problems with the 45MHz filter and the harmonic generation in the power amplifier.

80,40,20 meter CW
– Power level set on each band individually to 5 watts
– Green display line represents the -43 dBc threshold
– Second harmonic on both 80 and 40 is somewhat problematic as are odd harmonics out to 13th

80,40,20 meter SSB
– Power level set on each band individually to 5 watts CW then 1 kHz tone input level adjusted to produce the same 5 watts
– Green display line represents the -43 dBc threshold
– Second harmonic on both 80 and 40 is somewhat problematic as are odd harmonics out to 9th

17, 15, 10 meter CW
– Power level set on each band individually to 2 watts
– Green display line represents the -43 dBc threshold
– Harmonics can all be removed with a simple 34 MHz LPF. The filter included in the uBitx is more than adequate

17, 15, 10 meter SSB
– Power level set on each band individually to 2 watts CW then 1 kHz tone input level adjusted to produce the same 2 watts
– Green display line represents the -43 dBc threshold
– 17 meter spurs represented by markers 1 and 2 are problematic because only a close spaced, single band BPF can be used to remove them.
– 15 meter spurs at the low end need to be addressed.
– A single filter cannot cover these bands because of the close spaced 17 meter spurs.

Reference

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