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[AK4YA]

I have a nice QS1R SDR sitting on my desk here on HDSDR.  It doesnt have an antenna and Im using it to observe my transmitted signals.  Here is a set of pics, the first one is the no-antenna SDR with me not transmitting and the seconds is me calling CQ using FT8.  The power out is only about 30 watts.  Seems kinda trashy to me there.  Now 30w isnt much with this FT897D's max of 100, but even if I cut it down further I still seem to get the same pattern on my SDRs waterfall there.

The noise floor there is -105 (very tips of the noise), and each bar is 5db

[AK4YA]

I forgot to mention that Im not getting any ALC movement at all, which I believe is desired for digital modes.

[W9IQ]

It would be nice if you could show those screen shots with the dB units on the vertical scale and with a narrower bandwidth.

But as shown, any artifacts are -35 dBc so you don't have any significant problems. You might be overdriving the audio a bit.

- Glenn W9IQ

[W9IQ]

It would be good for comparative purposes to show a screen shot with just a carrier (no modulation) at the same output power.

- Glenn W9IQ

[AK4YA]

Ive got the scale on the left now as well.  The bandwidth before was as low as it goes 25ksps.  Here is it at 50ksps with the tune button on WSJTX being used at 30w

[N6YWU]

When testing a transmitter with an SDR on the same desktop, one has to be very careful to make sure they are not just measuring computer cable and power/ground wire conducted RF, rather than what's going out the transmitter's antenna connector to become radiated RF.

Even with both the transmitter and receiver connected to shielded dummy loads, any splatter you measure might just be desktop ground noise.  To avoid this, one could set up the SDR for remote operation from another nearby building or house.

[WA3SKN]

To keep the audio path in the linear portion (read distortion) of the curve (for the FT897), you probably want to limit the output power to about 20 watts max.  What does the distortion look like if you lower you output to 20 watts?  You do not want to use compression, you do not want to trigger the ALC.  This maxs the "signal-to-noise" ratio.

-Mike.