Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

500 - 3000 MHz Signal Generator

500 - 3000 MHz Signal Generator

500 - 3000 MHz Signal Generator

What is the simplest circuit for generating a sine wave or a square wave from 500 up to 3000 MHz? The signal does not need to be modulated; just a simple sine wave or square wave.

I would prefer the power output to be greater than -10 dBm at 50 ohms, but I can add an amplifier if needed.

The output frequency to be controlled by a voltage (using a potentiometer or a DAC) or digitally via I2C, SPI, etc.

I have looked at VCOs, but I have not come across any that can cover such a large frequency bandwidth.

Thanks in advance!

Operation Radiation: http://www.mrkenneth.com

RE: 500 - 3000 MHz Signal Generator

Agreed, VCOs do not cover the bandwidth directly - but here's a standard way of getting almost any frequency span:

Use a fixed frequency reference oscillator to feed one input of a mixer. A VCO feeds the other input of the mixer and the output is the difference of the two frequencies.

If you use high enough frequencies for both the reference oscillator and the VCO, the mixer difference output gives the required variable frequency span for a (relatively) small change in the VCO frequency.

RE: 500 - 3000 MHz Signal Generator

Mixing two VCO's together is a great idea.  You do end up with a lot of harmonics and spurious products, however.  Also, If you need low phase noise, that is probably not the way to do it.

RE: 500 - 3000 MHz Signal Generator

I've got a sweep oscillator that uses that very principle.

It's about 50 years old.

Uses the mains as modulation by varying the magnetization of a core in one oscillator and thus varying the inductance.

All thermionics of course...

RE: 500 - 3000 MHz Signal Generator

The simplest is : Mix a fix osc. and a VCO.

Depending your application, you may be able to
use the result without filtering.

How fast do you have to change the Fr.? Is step
change acceptable? Range switching (manual/auto) ?

Would mechanical tuning be OK? perhaps with motor ?
If square wave acceptable, you can tolerate harmonics?
What about other noise e.g. mixing artifacts?

<nbucska@pc33peripherals.com> omit 33 Use subj: ENG-TIPS
Plesae read FAQ240-1032

RE: 500 - 3000 MHz Signal Generator

I used for up to 200 MHz a regular ( TV IF type) pentode
connected as reflex klystron.( plate=reflector , 1/4
wave transmission line pair connected to gr3 and gr2, gr1 was AM)

<nbucska@pc33peripherals.com> omit 33 Use subj: ENG-TIPS
Plesae read FAQ240-1032

RE: 500 - 3000 MHz Signal Generator

Thanks to all for the quick replies!

I still do not quite understand the concept behind how a small change in the VCO frequency can produce a large change in the output frequency of the mixer. If the mixer takes the difference of the two inputs, would not a change in one of the inputs result in the same amount of change in the output of the mixer?

Example: Input 1 is at 1 GHz and input 2 is at 1.5 GHz. I assume the output is 0.5 GHz. When input 2 is increased to 1.6 GHz, then the output would be 0.6 GHz. So a 0.1 GHz change at the input still produces a 0.1 GHz change at the output.

I am surely misunderstanding something. :( Is the example above correct? I have tried searching on Google for similar applications/circuits (using a mixer, a VCO, and a fixed oscillator) to no avail.

The frequency change does not have to be quick. A second for 100 MHz is no problem. I would prefer to tune the frequency using a DAC in the final application.

nbuska, what do you mean by mechanical tuning? I would prefer everything to be controlled by a microcontroller.

For my application, I would like to generate a sine or square wave of a single frequency, so harmonics should be as low as possible. (Sorry, I do not have a quantatitive requirement, but perhaps -10 dB maximum for the harmonics?)Phase noise or any other artifacts should not be a problem.

By the way, nbucska, was your last post intended for another thread? I did not understand it at all...

Thanks in advance for the help!

Operation Radiation: http://www.mrkenneth.com

RE: 500 - 3000 MHz Signal Generator

It is all about percentage bandwidth.  It is pretty hard to make a 0.5 to 3 GHz VCO (140%).  It is easier to make a 10.5-13 GHz VCO (21%) and mix it down with a fixed 10 GHz signal.

RE: 500 - 3000 MHz Signal Generator

"Zeitghost == spirit of time" . The post was for anyone who may be interested in it.

You could switch the range
Let say F1= 10 GHz, F2=11 to12 gHz -- the difference
Fout=1 to 2 gHz. i.e. a 10% input change causes
100% output change.  ( The change in frequency
is the same but the ratio of the change to the
nominal frequency changes with the nominal freqency.

<nbucska@pc33peripherals.com> omit 33 Use subj: ENG-TIPS
Plesae read FAQ240-1032

RE: 500 - 3000 MHz Signal Generator

Thank you for the explanation.

Where can I find such a VCO that generates such high frequencies? I have not seen any over 3 or 4 GHz...

Are there other methods? What do commercial signal generators use?

Thanks in advance!

Operation Radiation: http://www.mrkenneth.com

RE: 500 - 3000 MHz Signal Generator

Evidently you don't know how to specify the generator.

Perhaps you could tell us what do you want to use it
and under what condition ( e.g. hobby, amateur building
or repair, manufacturing etc.)

<nbucska@pc33peripherals.com> omit 33 Use subj: ENG-TIPS
Plesae read FAQ240-1032

RE: 500 - 3000 MHz Signal Generator

I am just building this for fun, and will probably only produce one or two of these circuits.

I can only make this on double-sided FR-4 printed circuit board, so I am not sure whether I can use frequencies as high as 10 GHz without much loss...

Would using multiple VCOs to cover the entire bandwidth be easier? If so, how would I connect the output of all the VCOs together?

Thanks in advance!

Operation Radiation: http://www.mrkenneth.com

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close