Vector signal generator basic question - Page 1
Forum section: electronics / testgear

author: tkamiya
author_rank: Super Contributor
timestamp: November 09, 2018, 09:31:23 pm
content: So far, everything I do has been in scaler domain. I have an understanding on how wave is a "circle" and angle formed between sine and cosine will form its vector.But what I am not understanding is, there are MANY signal generators, like Keysight EXG, that it has only one output port. How can it form a vector without something else to form an angle with?I know it's vague but my understanding is so limited, this is the best I can do.

author: DaJMasta
author_rank: Super Contributor
timestamp: November 09, 2018, 10:29:24 pm
content: You can still have a signal with vector information, even if you don't have a reference signal available in the same way you can receive data over an antenna with phase information without having a locked phase/frequency reference.What makes it a vector signal generator is that it can create signals with phase information - almost any kind of complex modulation technique requires it, so any generator with an option to generate complex modulated signals must inherently have an architecture that allows for vector control.https://www.radio-electronics.com/info/t_and_m/generators/vector-signal-generator-vsg.phpIn essence, answering your question of how it makes a vector without an external reference output: it can form a vector against its own carrier tone, so if you compare the output signal against the phase of its own carrier, you can extract relevant phase information.

author: tkamiya
author_rank: Super Contributor
timestamp: November 10, 2018, 03:23:41 am
content: Paraphrasing what you said:Then, in order for phase shift to occur, you must have a carrier (of course) that is MODULATED? Just an modulated signal cannot have a phase shift.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 10, 2018, 04:00:26 am
content: Quote from: tkamiya on November 10, 2018, 03:23:41 amSure, you can modulate with the phase alone. For example:https://en.wikipedia.org/wiki/Phase-shift_keying

author: joeqsmith
author_rank: Super Contributor
timestamp: November 10, 2018, 04:01:20 am
content: Maybe you could find a copy of the ARRL handbook. This may make a good reference for you.

author: DaJMasta
author_rank: Super Contributor
timestamp: November 10, 2018, 04:54:20 am
content: You have a carrier tone that is your reference, then you can use a modulation scheme that changes its phase to convey information. Yes, it involves another signal in the generator architecture, but it comes out as the same modulated tone on a single output, and it's only the phase data you are modulating in, the carrier is effectively the same as any old RF signal source. On the receiver end you either need to listen to the signal for a while to figure out what the un-changed phase is, or you need a phase shift pattern to indicate the start of the data or another sort of reference point, but then your zero degree phase is effectively defined, so any variation from that can be interpreted as meaningful information, which means that phase information encoded into the signal is your modulation scheme (though, it can be combined with other schemes for more complex modulations).

author: tkamiya
author_rank: Super Contributor
timestamp: November 10, 2018, 06:16:14 am
content: That is very true.But as I see it, it is still a carrier modulated by a second signal, which modulation scheme happens to be that of a phase shift. I guess the good old FSK is this way.I do have a few ARRL manuals. Never thought to look there.

author: georgd
author_rank: Regular Contributor
timestamp: November 10, 2018, 07:56:14 am
content: Here is a good explanation of vector or IQ signal generation in today's popular video form:Georg

author: joeqsmith
author_rank: Super Contributor
timestamp: November 10, 2018, 04:48:58 pm
content: Quote from: tkamiya on November 10, 2018, 06:16:14 amPSK and FSK are different. An example of FSK:https://youtu.be/Mkec-Eyhg7c?t=342