I&Q Modulator questions....

[Fovakis]

Hi. I cannot understand the I&Q Modulator...:|

I am reading this one of mini circuits..**broken link removed**

It has I and Q inputs...and it write (DC to 5MHz) freq for the input..

1)is this analog signals or bit stream ?If is a bit stream how can it has 5MHz frequency?

2)The I&Q Modulators as i understand make QPSK/8QAM/16QAM etc modulation..so the message I and Q must be bit streams (symbols basic) and carrier analog signal..

30The output of a I&Q Modulator is exactly like the output of a AM-Modulator...USB, LSB , carrier...what is going on here?

George the noob

 

[D.A.(Tony)Stewart]

THE I&Q are analog signals with up to a 5MHz bandwidth used to multiple the LO which may be up to 80MHz. This can be used as an IF signal and upconverted.

The type of I&Q modulation is up to the user.

 

[Fovakis]

Hi SunnySkyguy. What is this?>

https://www.google.gr/search?q=I/Q+Moduator+block+diagram&aq=f&um=1&ie=UTF-8&hl=el&tbm=isch&source=og&sa=N&tab=wi&ei=D7maUZW7MYWsOrDngWg&biw=1280&bih=820&sei=E7maUcKFLc2KOKiLgOgK#imgrc=3A_YCn_-N-1NFM%3A%3BsqC4tsi7xpwFMM%3Bhttp%253A%252F%252Fwww.ni.com%252Fcms%252Fimages%252Fdevzone%252Ftut%252Fdhall_IQerror_fig3.JPG%3Bhttp%253A%252F%252Fwww.ni.com%252Fwhite-paper%252F5657%252Fen%3B537%3B211

5MHz is the fcenter not the bandwidth right? It has not any information about the bandwidth of the I and Q signal inputs.

The type of modulation is up to the user? I don't understand this...the modulator has a USB connector to PC, so i can choose the molulation? As i see no. How is that?


Sorry this modulator i want:**broken link removed**

The coaxial! I and Q ~~~ DC to 2MHz

 

[D.A.(Tony)Stewart]

min DC, max 2MHz

 

[Fovakis]

Re: I&Q Modulator questions....

Can you explain please how the modulation is up to the user? I cannot understand this...

Thanks

 

[mikerf]

IQ mixing is not magic, but it is 100% analogue, forget digits

You can use a pair of DACs to draw your I & Q signals, but they must be analogue when they are mixed.

The idea is to generate two 90 degree offset baseband signals, mix them with two 90 degree offset local oscillator signals then sum the result. The point is the result will look something like this:

MixA out = sinF1 + cosF2 MixB out = sinF1 - cosF2.. so when we add then together the cosF2 signals disappear. Of couse if our signals are not quite equal in size or slightly off in phase then this destruction of the unwanted sideband doesn't completely occur.


example: FSK.

generate 50kHz sinewaves 0degrees and 90degrees on I & Q. mix with 100MHz LO.. generate 100.05MHz output frequency. Now Invert one sinewave and you get 99.95MHz...

voila! you've just made a 1 and a 0 in FSK.

Mike

 

[Fovakis]

Hi Mikerf i like your reply!Thanks... i have some additional questions..

At the output of my DSP i have a 16-QAM analog signal fc=10KHz and BW=20KHz like this one: https://i1284.photobucket.com/albums/a578/fovos1/16QAM_zpse9ee0bf9.png

I have one output port at DSP.

So i can use a 90 degree splitter to create the same 16QAM like above but with 90 degree shift? So i will have I and Q signals

And then use a I/Q modulator to upconvert this one with carrier 100MHz?

George

 

[mikerf]

Ideally you need to be generating two signals from your DSP. One for I and one for Q.. you need, in some way, to create another port.

A passive phase splitter on the above signal would only give a fixed 90 degrees offset.. all your modulation would end up either high or low of your LO.

You could just centre your modulation at a fixed offset (that might be what you've done, I can't immediatly tell from your plot) then use a phase shifter to generate the 'Q' from the 'I' thus giving you an up converted signal permnently to one side of the carrier and an image say 30dB down on the other side of the carrier, you can't do this and get your output to work above and below your carrier.

Mike

 

[Fovakis]

Hi mikerf !Yes i must create another one port but at the time there is a problem so i test only with one port.

Can you please explain the above again as simple you can? I am noob in RF field and last 2 months i am trying to learn things...
thanks a lot !