O/PI modulator for 6 GHz signal, easy?

[badaboum]

Hello everybody,

first of all, i would like to thank you for reading this.
My, let's say, "problem" is very simple:
i would like to create a 0/PI modulator in order to modulate a RF signal (6GHz), that is to say, inverting the RF signal (+1 -1 like a ASK modulator) with a frequency between 500 Hz and 1 kHz.
1) Ok for creating the square wave generator (1 -1) with 500 Hz of repetition, if needed.
2) I've got the RF signal (6GHz)
3) and now...mixing...and that is my question. I don't really know how to choose the good design and which kind of component use:
- amplifier with G=1 and inverter amplifier with G=-1 driven (power on/off?) by the square wave, (not sure that is a good idea...)
- some transistors (FETs?) as switch driven by the square wave
- and otherwise, how can i realize the mixer? (schottky diode).

Thanks a lot!

 

[jiripolivka]

Hello everybody,

first of all, i would like to thank you for reading this.
My, let's say, "problem" is very simple:
i would like to create a 0/PI modulator in order to modulate a RF signal (6GHz), that is to say, inverting the RF signal (+1 -1 like a ASK modulator) with a frequency between 500 Hz and 1 kHz.
1) Ok for creating the square wave generator (1 -1) with 500 Hz of repetition, if needed.
2) I've got the RF signal (6GHz)
3) and now...mixing...and that is my question. I don't really know how to choose the good design and which kind of component use:
- amplifier with G=1 and inverter amplifier with G=-1 driven (power on/off?) by the square wave, (not sure that is a good idea...)
- some transistors (FETs?) as switch driven by the square wave
- and otherwise, how can i realize the mixer? (schottky diode).

One way to modulate your 6 GHz signal is to use two PIN switches and insert one and three-quarter wave line sections , one after another, by the modulation signal. There are such phase modulators available as MMICs, see "www.hittite.com".
Usig mixers is also possible, I-Q mixers are also available as MMICs at Hittite. Lower-cost devices are available at "www.minicircuits.com".

 

[badaboum]

Hello everybody,

first of all, i would like to thank you for reading this.
My, let's say, "problem" is very simple:
i would like to create a 0/PI modulator in order to modulate a RF signal (6GHz), that is to say, inverting the RF signal (+1 -1 like a ASK modulator) with a frequency between 500 Hz and 1 kHz.
1) Ok for creating the square wave generator (1 -1) with 500 Hz of repetition, if needed.
2) I've got the RF signal (6GHz)
3) and now...mixing...and that is my question. I don't really know how to choose the good design and which kind of component use:
- amplifier with G=1 and inverter amplifier with G=-1 driven (power on/off?) by the square wave, (not sure that is a good idea...)
- some transistors (FETs?) as switch driven by the square wave
- and otherwise, how can i realize the mixer? (schottky diode).






One way to modulate your 6 GHz signal is to use two PIN switches and insert one and three-quarter wave line sections , one after another, by the modulation signal. There are such phase modulators available as MMICs, see "www.hittite.com".
Usig mixers is also possible, I-Q mixers are also available as MMICs at Hittite. Lower-cost devices are available at "www.minicircuits.com".

Hi, thank you for this reply. Indeed, I was thinking of using IQ modulators but there are some internal amplifiers at the RF input in order to saturate the mixing signal and thus obtaining a good IQ modulated signal at the output. This is a problem for me because i want to keep the envelope of the RF signal (that is to say obtaining a ASK modulated signal but with the envelope of the RF signal). So, as you said, if i find a IQ mixer (1-6 GHz) without any internal amplifier, it could work....

 

[FvM]

I don't see what the problem has to do with I/Q modulation. A basic balanced modulator is all you need.

 

[biff44]

go to mini circuits, buy a $1 double balanced mixer with a DC coupled IF port, put a 100 ohm resistor in series with the IF port, and put +/- 1 volt on the IF port thru the resistor. You will get almost perfect 0/180 degree phase shift

 

[badaboum]

Hi Biff44,
thanks a lot for this precious help.

 

[biff44]

the only problem is you will have maybe 6 dB of loss with the Double Balanced mixer approach, but the phase should be spot on.

 

[badaboum]

yep, but if i understand well, the aim is to use:
- the IF as the input for the square wave (PRF about 500 Hz),
- the LO as the input of the RF signal (6 GHz)
- the RF input as the output.
Does it sound good? that's mean i've to take care about my RF signal level in order to enter the LO input with sufficient power (depending on the choice of the level mixer).
thanks.

 

[tony_lth]

make sense, but one point needed focus is that square wave may need LPF when as IF input.
Banlanced IF needs +/-1 and -1/+1 as input.