# VCO modulating voltage input

#### electronicNovice

Jul 26, 2015
11
I have RF VCO module. I have 2 inputs Vcc (Power supply at 5V). Then I have modulating signal 0-4.5V. What should I do with the modulating signal? Can I short it to the GND (The GND on the VCC)? What is the modulating signal for? It is 1.2GHz VCO module. I need the VCO to be in the Box. It is not for a bench testing. If anybody have a reference for VCO book or manual that would be great.
Thanks

#### bertus

Moderator
Nov 8, 2019
2,797
Hello,

Do you have a datasheet or other detailed info on the module?
I would take two resistors to make a voltage divider, to fix the modulation input on a fixed value, inside the range of the mentioned 0-4.5 Volts.

Bertus

#### electronicNovice

Jul 26, 2015
11
I do not have a datasheet. But what is the modulating signal for? Should be ac or DC?? I can bring DC signal to it no problem. With a separate battery or same battery with voltage divider as you suggested.

#### bertus

Moderator
Nov 8, 2019
2,797
Hello,

Where did you get the VCO module?
What is the frequency range?
The modulation input is likely to shift the frequency of the module, like FM modulation.

Bertus

#### electronicNovice

Jul 26, 2015
11
Hello,

Where did you get the VCO module?
What is the frequency range?
The modulation input is likely to shift the frequency of the module, like FM modulation.

Bertus

Ok. If I ground it then should be fine also right?? Because then the modulation will be zero (like f + delta (f) = f )

#### bertus

Moderator
Nov 8, 2019
2,797
Hello,

I would expect the voltage be the half of the range, so about 2.25 Volts.

Bertus

#### electronicNovice

Jul 26, 2015
11
Hello,

I would expect the voltage be the half of the range, so about 2.25 Volts.

Bertus
ok thanks

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
12,903
Do you know what a VCO is?
A VCO is a voltage controlled oscillator. Meaning that you change the frequency by applying a control voltage. When you fix the control voltage anywhere within the allowed range (0 V ... 4.5 V) the frequency will be fixed, too.
You will find the relationship between control voltage and oscillator frequency in the VCO's datasheet.

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