Friday, November 3, 2023

Gamma Dog - Assisted Squelch Auto-Set (ASAS) / "Smart Squelch" System

One of the main features of the Gamma Dog project is the unique Squelch System controlling the audio output.

The Gamma Dog's Squelch System works by detecting a differential between the Natural Radiation Background (NRB) and the current detected rate coming from the scintillating detector. The Squelch system mutes the audio and sets a threshold level at the same rate as the NRB and when the currently detected rate exceeds this threshold level, the audio output is enabled.
In other words, the current rate is treated as a relative rate to a pre-set reference point (the Squelch Level) and the absolute value is insignificant for the Squelch System.

Gamma Dog will sample the NRB rate on startup or any time when the user activates an "Auto-Set" by pressing and holding the blue Squelch button or using one the Gesture Control triggers. 
When Auto-Set is activated, Gamma Dog will use one of 3 methods to determine the Squelch Level (the method used is selected by Menu Item #20):
    1. Single Sample - Squelch Level will be set to the currently detected rate, using a single sample at the moment when Auto-Set is triggered.
    2. SD5 method (default) - The Gamma Dog will average the rate over the last 5 seconds, calculate the Standard Deviation and then use the upper bound of 1-sigma threshold to set the Squelch Level.
    3. SD10 - same exact method as SD5 but rate is averaged over the last 10 seconds before Standard Deviation is calculated. The 1-sigma Upper Threshold is calculated by summing the average rate and SD.

A critical aspect to the operation of the instrument is a properly set Squelch Level.
This makes the squelch system responsive to small fluctuations detected just above the background level.
The "sweet spot" is when the current background rate only occasionally opens up the Squelch System but not too often - up to 3-4 times per minute.

The Squelch level can be Auto-Set (by sampling the Natural Radiation Background rate) or adjusted Manually, when the user is modifying the already set level with the GD Squelch Level +/- controls.
In either case, if the Squelch Level is incorrectly set against the NRB level, this could result in missing possible specimen finds or less-than-optimal Squelch functionality. 

One of the problems Charles and I encountered in the field while surveying and prospecting different areas is the Squelch response to highly localized Natural Radiation Background Levels.

For example - when surveying a REE deposit in Southern New Mexico we realized that the NRB is extremely localized - there are very well defined areas of the pegmatite exhibiting very high Natural Radiation Background ("hot zones") and just a few yards away, other areas with comparatively very low NRB ("cold zones"). This meant that we had to constantly sample the NRB rate and reset the Squelch system manually, every time we crossed over from one zone to another. On the other hand, both zones in this pegmatite produced very nice Euxenite crystals.

In this situation, if we focus only on moving through the terrain without paying attention at the current squelch level, we can enter an area where the NRB rate is much lower than what the squelch is set to and any small peaks or fluctuations, possibly indicating the presence of a specimen will be masked and hidden by the squelch system (that is if the rate is not promptly re-adjusted). 
It could be some time, before one realizes that the instrument has been quiet for too long due to a Squelch rate set too high for the current NRB Level.
The opposite is also true - crossing from an area with low background rate to an area with high NRB will cause the Squelch system to stay constantly open which defeats the purpose of having it in first place.

To resolve this issue, we came up with the "Smart Squelch" System or Assisted Squelch Auto-Set (ASAS).

The purpose of ASAS is to constantly monitor the current rate, compare it to the state of the Squelch System and detect conditions which can indicate that the Squelch rate might be incorrectly set for the current background. 
Once ASAS determines that the Squelch Level needs an adjustment, it will trigger an Auto-Set action, same as if the user pressed the Auto-Set button and it will re-sample the NRB.
This allows for very easy, smooth and worry-free operation - ASAS System does all of the necessary adjustments when they are needed, and the user can focus on the terrain and not on the instrument. 

The implementation of ASAS is different between the one I designed, and the one Charles is using in his GD version. The main difference is that in my version, due to the availability of display, menu system and persistent configuration parameters, I can configure many internal aspects of the ASAS behavior and make it customizable and more flexible.

This is how ASAS monitors the state of the Squelch System.
Out of the 19 Configuration Menu Items, there are 4 menu items dedicated to the ASAS system.

In my implementation, there are 2 separate timers configured with a single menu item, setting the period for a condition to be present continuously, before an Auto-Set is triggered.
One timer is reset every time the Squelch is Open, while the other timer is reset every time the Squelch is closed. Basically, I monitor the state of the Squelch System and cross-reference the state with the currently detected rate.
The timers can be set for 15, 30, 45 or 60 seconds.

One functionality I added to ASAS is the ability to "decide" if Squelch Auto-Set is needed while the squelch has been open for a long time.
When the user needs to pinpoint the location of a specimen, it often helps for the squelch to stay open so variations in the pitch of the audio tone can be monitored closely and in this case Auto-Set should not be triggered.
In my implementation of ASAS, I have a menu item which specifies a second, virtual threshold level which, when exceeded, it will prevent the Auto-Set from activating due to continuously open squelch by resetting the Open Squelch Timer.

The logic behind this is that if a specimen is found and the user is now trying to localize it, the detected rate will be vastly higher than the NRB / Squelch Rate and not just slightly above it - the ASAS system will identify this large difference in rates and it will not trigger an Auto-Set, thus allowing the user to listen to the audio tone. 
The ASAS Reset Lvl, determines the height of the virtual "localization rate" as a percent of the current rate above the squelch rate. This value can be configured as 37%, 50%, 62%, 75%, 100% and 150%.

For example - if ASAS Reset Lvl is set to 100%, the Squelch Rate is set to 200 CPS and the detector reports a current rate of >400 CPS (or exceeding the Squelch rate by more than 100%, ASAS will not trigger an Auto-Set assuming the user has found a specimen and just tries to pinpoint it. If the rate drops below 400CPS then the continuously open squelch condition will trigger an Auto-Set when the timer for it expires.

Another functionality in my ASAS System is adding a "padding" (called ASAS Tolerance) between Squelch level and current rate while the squelch is monitored for continuously closed condition. The amount of padding or tolerance is adjustable with a menu item (ASql Toler) and specifies in CPS how low the current detected rate must drop below the Squelch Level before the timer of the continuously closed squelch activates an Auto-Set action.
This differential can be set from just below the current Squelch Level to a few hundred CPS lower and it is intended to add adjustable damper for the response to constantly closed squelch.
The options are 100 CPS, 150 CPS, 200 CPS, 250 CPS and 500 CPS

By default, the ASAS System is deactivated and can be toggled ON/OFF by double-clicking the GREEN Button.
The last menu item of the ASAS System configures whether the system is activated automatically at the startup of the instrument, or the user activates it at a later time.

The ASAS System in action. 
When the ASAS is active, the "Sql" indicator above the Squelch Level is replaced with "(A)". The timeout is set to 15 seconds in this demonstration.
The two bars on the display shrink, while showing when a timer is about to expire - the top bar is for Open Squelch conditions and the bottom bar is for Closed Squelch conditions. A full width bar represents the maximum time and dot is displayed for the trigger point.

Charles searching for REE in Petaca, NM while using the "Smart Squelch" System.
The Gamma Dog produces distinctive beeps every time when the Automatic Squelch System is triggered to re-sample the Squelch level.