SmartSDR v4.2.18 | SmartSDR v4.2.18 Release Notes
SmartSDR v3.10.15 | SmartSDR v3.10.15 Release Notes
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Small UI bug/string in 4.2.18
I am not too sure how many new "hams" will know what PACTOR is - I presume commercial users will of course, but this was DIGITAL MODES if I remember correctly pre this version?
Also - not sure where to post bug reports - as a search for "bug" was too noisy.
73 Steve G0RFC
Comments
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Obviously wait for Flex to respond but I believe this is not a bug. It is a correction. It was called Digital Modes but users were checking it to on for all DIGI modes which was the wrong thing to do.
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Hi Steve,
Eric is right, this box should not be ticked for normal operation of digital modes. When you tick this, it replaces the RX filters in DIGI modes with a low order wide IIR filter that has terrible adjacent channel filtering and also has undesirable roll-off within the passband. But what it does offer in exchange is very low latency that is required for PACTOR like modes.
The latency of the normal filters (without this box ticked) is absolutley fine for all other digital modes and you really don't want all the downsides to enabling this unless you are using PACTOR.
73 Jonathan
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Hi Jonathan,
That’s really helpful, thank you.
It’s an interesting shift in how the feature is framed. I completely understand the trade-off around phase distortion and group delay, particularly in higher speed HF modems. With modes such as STANAG 4285/4539 or other MIL-STD waveforms, where coherent demodulation and tight symbol timing recovery are critical, excess filter latency and non-linear phase can start to impact equalisation performance and overall decode reliability.
In those cases, reducing group delay through lower order filtering can be beneficial, especially where the modem is already working close to the edge in terms of SNR or dealing with selective fading. That said, the compromise in adjacent channel rejection is quite significant, so it becomes a balancing act depending on band conditions.
PACTOR does feel like a slightly unusual headline use case here, given its relatively robust ARQ design and tolerance to channel impairments. I might have expected this to be positioned more broadly around phase-sensitive or high symbol rate modes where latency directly affects demodulation accuracy.
Appreciate the clarification, it makes sense in context.
73, Steve G0RFC
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It was originally added for digital modes that have a fast RX/TX changeover like Pactor with the trade off that the skirts are wider.
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Thank you @Mike-VA3MW that clears that up. Did some work many years ago on a hardware/software modem suite and all the nuances of the varying requirements around each mode has come flooding back 😂😂😂
73
0
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