Modulation Toolkit Question

[Patrick78]

Hello,

I am playing around with the modulation toolkit currently and have two questions:

In the attached example I ASK modulate the bit sequence "1010" and graph the output of the "MT Modulate ASK" block. With M=2, Symbol Rate = 1khz and Samples per Symbol = 16 and Pulse shape filter disabled I get this output:

1. Questions: Why do I only get 8 samples for the first bit?

When I change the Samples per Symblo to 32 (all other parameters unchanged) I get this ouput:

 

2. Questions: I would have expected to see 32 samples per symbol now. Instead it changed to 16 sampels for a "1" and 48 samples for a "0". What is happening here?

As said I am still learning and trying to understand the fudamenrtals so I would appreciate if anyone could explain that behaviour to me.

Thanks,

Patrick

[cochenob]

It's been awhile since I've used some of the Modulate VI's in the Toolkit...but I seem to remember a setting where the first few samples of a stream would be deleted on the presumption that it would include transients of the pulse shaping filters the first time you ran bits through them.  There's probably a boolean value somewhere that you can set that controls this behavior, and whether or not you keep those first few samples that are influenced by the group delay, or chop them off.  I also think this happens even in your case when you don't have any pulse shaping (the pulse shaping filter isn't actually bypassed, it's just a square), but I could be mistaken.

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Brandon

[Patrick78]

Thank you Brandon. That makes sense. I can't find any parameters to change this but maybe it is not intended to make this user configurable.

I also figured out what was going on regarding my second question. The pulse shaping filter samples per symbol needs to match the samples per symbols used in the system paramters, even if the filter is set to "none".

Thanks,

Patrick