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5.21 - I/Q Spikes, Reversal and I/Q Balancing (IQ)
This spike will appear sometimes as a result of the I/Q signal processing by an SDR being out of DC voltage balance. This is not unusual. You can zero it out by simply tuning to a nearby zero signal portion of the spectrum, then pressing Z or →Left-click
ZE, and waiting about ten seconds — watch for 
ZRO to stop flashing. The spike should quickly disappear.
If you're still having problems, particularly in the case of a soundcard based SDR like the FCD, right-click on and see if adjusting the phase and balance controls in that dialog can improve the situation. Make sure that 
On near the bottom of the dialog is checked.
With any SDR, and notably with those made from mass produced SDR components, there may be DC and phase imbalances between the I/Q signals output by the device. Right-clicking on provides access to phase and balance correction tools that can be switched in and out with the associated checkbox. If you do not check On , no balance or phasing correction is applied, regardless of the settings. These settings affect ALL devices and recording playback as well. COR lets you know if correction is on.
5.21.0.1 - Reverse IQ, Reversed Sidebands, Reversed Tuning
If you find that your SDR setup has the I/Q signal components swapped, you can compensate for this by →Right-click and checking L-R Swap . I/Q reversal is made obvious by the upper and lower sidebands acting as if they were the opposite sideband; other strange things can happen too, but that's the most obvious tipoff. This affects all devices.
Reversed sidebands and tuning direction can also occur when you sample an IF feed from a radio and the signal has been inverted from its normal low-to-high frequency state by the mixer signal being on the odd side of the signal. Again, the solution is →Right-click and check L-R Swap .
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