PureSignal 2.0 Release Notes & Operation
Posted: Tue Mar 05, 2019 10:17 pm
First, read the document called PureSignal.pdf that is installed alongside of Thetis.exe, in C:\Program Files\OpenHPSDR\Thetis (or Program Files x86 if you installed the 32-bit version). It is attached below for convenience.
Also read the PureSignal sections of Laurence Barker's manual, which can be found in the same folder alongside of the PureSignal.pdf.
Some additional notes on basic PureSignal operation:
For PureSignal (PS) to function at all, the ALC output MUST peak essentially at 0dB so that the TX signal traverses the entire DAC range. This is always a requirement and has nothing to do with the amount of analog feedback provided through the feedback network and receiver (other than obviously as peak TX output goes up so does peak analog feedback level). Read more about feedback levels below.
The ALC algorithm in Thetis (and PowerSDR mRX before it) is an intelligent, look-ahead, soft-limiting algorithm. This makes it quite safe to adjust audio levels such that peaking 1 to 3 dB higher than 0dB ALC will not have any audible effects and doing so provides for much more positive and consistent PureSignal measurement frequency. For some digital modes this may not be optimum, but for phone the effects are essentially inaudible.
It is easiest to use the "ALC Group" metering mode. ALC mode only shows ALC ≤ 0dB. ALC Comp mode only shows ALC ≥ 0dB. ALC Group combines both metering modes conveniently into one.
ALC not reaching 0dB has always been a very common cause, if not the most common cause, for PS not working.
Analog feedback levels (colors refer to the original color scheme, this can be reversed in the settings if desired):
ADC Overload indicated on the spectral display status line: if you are in ADC overload, you will likely get disastrous PureSignal results as the feedback will be terribly distorted – this is totally unacceptable for operation.
Feedback indicator blue: overload to 6dB below overload. In this range you MIGHT get a little degradation in IMD performance with PureSignal, depending upon the passive intermodulation performance of the filters, transformers, etc., preceding the ADC.
Feedback indicator green: if you’re in this zone, you are close to using all the ADC dynamic range and PureSignal performance should be great, assuming no other impeding factors.
Feedback indicator yellow or red: your feedback signal is getting weaker and weaker and Puresignal performance is degrading accordingly as you use less and less of the ADC dynamic range for your feedback. The less dynamic range you use, the worse your performance is likely to be. These should be considered the caution and unacceptable values for feedback level on the low side.
More technical detail on how to calculate feedback levels, including coupler and attenuator selection, can be found in this topic: https://apache-labs.com/community/viewtopic.php?f=20&t=2384
Also read the PureSignal sections of Laurence Barker's manual, which can be found in the same folder alongside of the PureSignal.pdf.
Some additional notes on basic PureSignal operation:
For PureSignal (PS) to function at all, the ALC output MUST peak essentially at 0dB so that the TX signal traverses the entire DAC range. This is always a requirement and has nothing to do with the amount of analog feedback provided through the feedback network and receiver (other than obviously as peak TX output goes up so does peak analog feedback level). Read more about feedback levels below.
The ALC algorithm in Thetis (and PowerSDR mRX before it) is an intelligent, look-ahead, soft-limiting algorithm. This makes it quite safe to adjust audio levels such that peaking 1 to 3 dB higher than 0dB ALC will not have any audible effects and doing so provides for much more positive and consistent PureSignal measurement frequency. For some digital modes this may not be optimum, but for phone the effects are essentially inaudible.
It is easiest to use the "ALC Group" metering mode. ALC mode only shows ALC ≤ 0dB. ALC Comp mode only shows ALC ≥ 0dB. ALC Group combines both metering modes conveniently into one.
ALC not reaching 0dB has always been a very common cause, if not the most common cause, for PS not working.
Analog feedback levels (colors refer to the original color scheme, this can be reversed in the settings if desired):
ADC Overload indicated on the spectral display status line: if you are in ADC overload, you will likely get disastrous PureSignal results as the feedback will be terribly distorted – this is totally unacceptable for operation.
Feedback indicator blue: overload to 6dB below overload. In this range you MIGHT get a little degradation in IMD performance with PureSignal, depending upon the passive intermodulation performance of the filters, transformers, etc., preceding the ADC.
Feedback indicator green: if you’re in this zone, you are close to using all the ADC dynamic range and PureSignal performance should be great, assuming no other impeding factors.
Feedback indicator yellow or red: your feedback signal is getting weaker and weaker and Puresignal performance is degrading accordingly as you use less and less of the ADC dynamic range for your feedback. The less dynamic range you use, the worse your performance is likely to be. These should be considered the caution and unacceptable values for feedback level on the low side.
More technical detail on how to calculate feedback levels, including coupler and attenuator selection, can be found in this topic: https://apache-labs.com/community/viewtopic.php?f=20&t=2384