PureSignal 2.0 Release Notes & Operation

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w-u-2-o
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PureSignal 2.0 Release Notes & Operation

Postby w-u-2-o » 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
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w-u-2-o
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PureSignal 2.0 Release Notes

Postby w-u-2-o » Sun Oct 27, 2019 1:46 pm

The primary objectives for PureSignal 2.0 are:

* Make the algorithm more robust. Improve ease of automatic calibration and improve operation (1) for "difficult" amplifiers, and (2) for amplifiers being driven into heavy gain compression. ("Difficult" amplifiers are generally those with significant memory effects, typically poor plate/drain and bias voltage regulation.)

* Streamline the user interface. In particular, (1) place Auto-Calibrate OFF/ON control and the 'Feedback' and 'Correcting' indicators on the main console, (2) reduce the screen real-estate required for the 'Linearity' window, and (3) separate 'Advanced' controls that only need to be accessed for diagnostic purposes or special situations.

SIGNAL PROCESSING

In the 'Advanced' controls section, the 'Calibration Information' panel is visible, and, there are four new controls that were not in PureSignal 1.0. These new controls represent new functionality that has been added and they should normally be left at their default settings. The controls are:

** 'PIN': Applies a priori knowledge of the required amplifier gain and phase correction in situations where the collected samples are insufficient for optimal calibration. This need can arise when the radio is not being properly driven to allow sample collection over the entire operating range, or due to some other fault or incorrect operation. This is very useful when there is a significant voltage regulation problem in an amplifier and, therefore, the gain and phase of the amplifier appear somewhat "unstable" as PureSignal collects feedback for calibration.

** 'MAP': Changes the sample-collection requirements to allow easier calibration in situations where the amplifier is detected to be in heavy gain compression. This is done by mapping the collection intervals to a different set of intervals based upon the level of compression. Note that this relaxation in sample-collection requirements MIGHT cause some degradation in high-order IMD. This is adaptive; the extent of the remapping depends upon the level of compression. If there is no compression, this function has no effect.

** 'STBL': Substantially separates the "static non-linearity" of the amplifier from the memory effects before computing the correction. This is a step toward further work on memory effects in a future release. When this is enabled, the "blue" and "yellow" displays on AmpView will show the extracted static non-linearity.

** 'TINT': A largely experimental feature allowing selection of the size of the upper interval within which samples are required to be collected. The dB value reflects the reduction from full-scale. For example, 2.5dB means ~75% of full-scale voltage or ~56% of full-scale power. This should normally be left at the default setting of 0.5dB (~94% of full-scale voltage and ~88% of full-scale power). This feature can be useful in situations where an external processing system, for example a Digital Audio Workstation, is used to precisely control the audio drive amplitude. Note, however, that Auto-Attenuate should probably be disabled when not driving to full-scale as there may not be enough information to accurately calculate its setting which can result in instability in the attenuator value.

NOTE ON AMPLIFIER GAIN COMPRESSION AND TUNING. For modes requiring linear amplification, it is NOT recommended to drive amplifiers into heavy gain compression or "flat-topping." Doing so will increase IMD significantly when PureSignal is NOT active and may increase it slightly when PureSignal is active, due to heavy reliance on the MAP function. Driving into heavy compression will not increase your peak output power by any meaningful amount and, when using PureSignal, it will not increase your average power at all since PureSignal will remove the compression in the output signal to restore linearity. For vacuum-tube amplifiers with 'Tune' and 'Load' controls, if your amplifier has excess power capability compared to your desired output level, you can generally avoid heavy gain compression by tuning the amplifier for a higher power level than your desired output and then backing down the drive level to achieve the desired output. The down-side of this tuning approach may be a slight reduction in amplifier efficiency. It should be noted that there are "proper" ways to increase your average transmit power; those include the use of the Compressor and the CESSB Overshoot Control algorithm.

USER INTERFACE

PureSignal Auto-Calibrate mode can now be used without opening the "Linearity" window. Simply click the "PS-A" button in the upper-left region of the console to activate PureSignal Auto-Calibrate. The "PS-A" setting will also be remembered in the database. Indicators for Auto-Calibrate functionality will appear immediately below the panadapter display area, on the right side. "PureSignal 2.0", when displayed in green, indicates this functionality is active. Immediately to the right of that, the "Feedback" indicator will flash each time there is a new automatic calibration and the "Correcting" indicator will light when correction is being applied. Note that the color-scheme of the PureSignal items will not follow the color scheme of the other below-panadapter information. This is because, for PureSignal, color is used to indicate the status of the various items:

OFF/ON - Blue (Auto-Calibrate OFF), Green (Auto-Calibrate ON)
Feedback Level - Red (too low), Yellow (marginally low), Green (just right), Blue (too high)

Correcting - Green (correcting), Yellow (attempting correction but with marginal feedback level), Black (no correction being applied)
Note that the "PS-A" button is dominant over the "Disable PureSignal" check-box in Setup. In other words, if you click "PS-A" to turn-on Auto-Calibrate, if "Disable PureSignal" was checked, it will become Unchecked. While "PS-A" is active, you will NOT be able to check "Disable PureSignal".

The "Linearity" window has been stream-lined. You can click "Advanced" to expand the window to show the advanced signal processing controls and indicators; however, it is expected that the typical operator will leave settings at defaults and has no need to open this section. The width of the "Linearity" window has been expanded to match the width of the "AmpView" window, making it easier to stack the two on the screen.
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DL1KD
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Re: PureSignal 2.0 Release Notes

Postby DL1KD » Mon Mar 28, 2022 5:47 pm

Hello Scott,
after the 2.8.11 release of Thetis, as far as I know, Richie made some more modifications to PureSignal 2. (As of today 21K9)

Can you add/explain these changes here in this thread?

For example:
"Quick Attenuate Response"

See attached screenshot
puresignal2.png
puresignal2.png (17.4 KiB) Viewed 18150 times


Thanks
Alex DL1KD
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w-u-2-o
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Re: PureSignal 2.0 Release Notes

Postby w-u-2-o » Mon Mar 28, 2022 6:30 pm

See here:

viewtopic.php?f=9&t=3817&p=14610&hilit=quick+attenuate+response#p14610

Quick attenuate response option added in PS Advanced linearity window. When selected feedback level is sampled at 20ms instead of 100ms
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rbduck
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Re: PureSignal 2.0 Release Notes

Postby rbduck » Mon Mar 28, 2022 7:19 pm

DL1KD wrote:Hello Scott,
after the 2.8.11 release of Thetis, as far as I know, Richie made some more modifications to PureSignal 2. (As of today 21K9)

Can you add/explain these changes here in this thread?

For example:
"Quick Attenuate Response"


I'm not going to attempt to explain them. My terminology is greatly lacking sufficient accuracy. I find it easier to understand a lot of the changes by breaking them out of the list and group them.
There is nothing wrong with the way he did it. If I had a memory like Scott and Richie have I'd be ecstatic. I'm creating my own lists of sorts. Here is the list I made from what I found in update 21K9b. There are a couple of others that had mention of PS. I did not find any value in those and did not list.

1. fix: PS 'Correcting' should show again on main ui if PS-A is toggled and PS is in correcting state
2. fix: PS client side state machine prevented from turning off autoCal when it needs to stay on. Fixes issue with PS not calibrating when PS-A button is cycled outside TX
3. add: quick attenuate option added to ps form. If PS auto-atten is on and this is enabled, ps feedback calculations will be made 5 times more often
4. add: quick attenuate response option added in PS Advanced linearity window. When selected feedback level is sampled at 20ms instead of 100ms
5. change: PS client loops do not run if power off
6. change: 31dB TX attenuation is now only applied when PS-A is off, and mode is CW when tx'ing
7. change: PS loop(s) are now in own thrfix: background colour fix for Advanced button in PS formead instead of a UI timer(s)
add: right click ps-a button opens linearity form
8. fix: PS enabled with DUP off will now show in correct position in spectral display
73
Ruben
NB4R
Apache-Labs Anan 7000DLE MKII Black -- Thetis 2.10.3.6 dev_2 -- Windows 11
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DL1KD
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Re: PureSignal 2.0 Release Notes

Postby DL1KD » Tue Mar 29, 2022 9:03 am

Thanks Ruben!,
if you are not constantly on the ball and read all threads crosswise, it is almost impossible to understand the background and also technical reasons for the changes. I think that's how many others here feel as well.
But with your summary Ruben, is already helped me for the time being.

73
Alex DL1KD
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ramdor
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Re: PureSignal 2.0 Release Notes

Postby ramdor » Tue Mar 29, 2022 12:25 pm

and one more....

add: PSpeak will be saved if you adjust it, default button to reset it (linearity form)

The PS peak value is related to firmware version, which in all actuality is chosen based on protocol in use. Some more info in this thread... viewtopic.php?f=20&t=4097

Richie.

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