TCIskimmer Lite - quick start
DDS
The first parameter a TCIskimmer Lite user has to get familiar with is DDS (Direct Digital Synthesizer frequency). Many SunSDR/ESDR3 fans have never even heard of it, although it has been part of the TCI protocol since day one.
Up until now an ordinary ESDR3/SunSDR user never used DDS. But with TCIskimmer Lite the situation has been changed, because DDS is one of the key TCIskimmer parameters.
Where DDS is documented: https://github.com/ExpertSDR3/TCI
What DDS is and what it is for in TCIskimmer
When the skimmer requests a slice of the RF panorama stream from ESDR3, it specifies the width of that slice (48000 by default).
And DDS is the centre of that RF panorama slice.
When TCIskimmer is connected to ESDR3, the exact DDS frequency is shown among the information in the top left corner. And the line below it shows the actual decoding range.
How to control the DDS value in ESDR3
- Option 1: point the mouse at the panorama, press and hold the right mouse button and drag the panorama left and right
- Option 2: point the mouse at the VFO frequency indicator and change the value
- Option 3: ON/OFF Use IF in E-Coder
By changing the DDS value you change the TCIskimmer decoding limits at the same time
Signal decoding window
The second parameter a TCIskimmer user has to understand is the signal decoding window
The TCIskimmer signal decoding window is NOT the ESDR3 band-pass filter width. These two parameters are NOT related in ANY way.
How the TCIskimmer signal decoding window is applied
At start-up the skimmer takes a 48000 kHz wide RF panorama stream and slices it into 'bins' 75 (or 50) Hz wide. Each bin is decoded individually if the decoder has found a CW signal in it.
Noise Threshold
The third parameter a TCIskimmer user has to understand is the Noise Threshold level (default value +10dB). It is a kind of decoder "sensitivity" (not exactly so in fact, but this is the closest term).
The decoder decodes a signal above the noise level - everybody knows that. The Noise Threshold level sets the signal level above the noise level at which decoding can start at all. That means that if a signal has never crossed the threshold set in Noise Threshold, then this signal will not be decoded (but there is an exception, more on it later).
The default Noise Threshold value (+10dB) in TCIskimmer assumes that Preamp/ATT in ESDR3 is set either to 0dB or to +10dB - it is in this case that the default Noise Threshold value of +10dB works as intended.
If you had to switch ATT to -10dB, then you will have to move the Noise Threshold value "down" as well (not necessarily by 10 "down", but by 8 for sure).
Keep in mind that the Noise Threshold parameter is strictly individual and it is likely you will have to tune it a little for your antenna and your conditions.
The dependency of the Noise Threshold value is direct: the lower the value -> the more "sensitive" -> the more "noise" bins are passed to the decoder -> the higher the CPU load.
Minimum number of repeats
The fourth important parameter - the minimum number of repeats sets how many times in a row a callsign has to be decoded before it appears on the panorama and in the bandmap.
The default value differs between decoders: for Decoder 1 it is 1, for Decoder 2/3 it is 2. It is because of these default values that Decoder 1 may look like it "spams" much more. If so - change the value to 2.
Video Tutorials
Quick start and basics (Link 1)
Quick start and basics (alt Link 2)
