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Topic: 2.1GHz RF sig gen/control (Read 1 time) previous topic - next topic

Piplodocus

Hello!

I want to make a small CW sig gen that transmits at 2.122 GHz, with quite accurate frequency. How would I go about that? I figured there might be a way to use some kind of oscillator chip, give it a high frequency input + another tuning signal from and arduino (and/or possibly provide test data patterns). The level accuracy isn't too important but would be nice to be controllable up to say 50 to a few hundred mW output?

Any ideas how feasible this is? Any pointers to similar projects or ideas on line? Or general guidance on what path I should go?

Cheers,

Phil.

MarkT

What band is that frequency in?  I don't recognise it.
[ I won't respond to messages, use the forum please ]

Piplodocus

European 3G (UMTS FDD band 1) downlink

terryking228

#3
Nov 01, 2012, 12:33 pm Last Edit: Nov 01, 2012, 01:38 pm by terryking228 Reason: 1
Hi, I think you are looking for a DDS (Direct Digital Synthesizer) chip / Module. Fortunately today there are some at that frequency. See:

http://www.i0cg.com/ad9912___1_ghz_dds.htm
http://www.analog.com/static/imported-files/data_sheets/AD9956.pdf

Google "DDS 1.2 Ghz" etc...   (Yes, meant 2.1 Ghz)  What's a few cycles between friends?? :)
Regards, Terry King terry@yourduino.com  - Check great prices, devices and Arduino-related boards at http://YourDuino.com
HOW-TO: http://ArduinoInfo.Info

Piplodocus

Thanks. I assume you mean 2.1ghz not 1.2ghz (unless I'm missing something and I should use some kinda frequency doubler)

MarkT

So the first step is to get a licence for the frequency?
[ I won't respond to messages, use the forum please ]

Piplodocus

Not if it's being used in a screened room! :)

oric_dan

What the OP wishes to do is learn about "cell phone jammers".

Piplodocus

Kinda! I want to make sure NOT to jam or degrade any of the UMTS band, except while stopping something connecting to a certain cell by jamming the downlink frequency it close range (within a few metres). Just a manually tunable fixed frequency narrowband signal would probably do, I'm just not sure how feasible that is.

Basically this principle/method works fine using a Rohde and Schwarz 20 GHz sig gen I have here, giving 15 dBm into a poorly tuned antenna. I can't have this here and use an expensive bit of test gear we need for other stuff, just for this though.

If I can make an oscillator that doesn't drift much and stays at 2122.4 MHz without varying out of it's 5 MHz channel bandwidth, then the simpler the better to be honest! All RF chips of this frequency seem to involve a certain amount of complexity and control for synthesis that I've found. 

retrolefty


Kinda! I want to make sure NOT to jam or degrade any of the UMTS band, except while stopping something connecting to a certain cell by jamming the downlink frequency it close range (within a few metres). Just a manually tunable fixed frequency narrowband signal would probably do, I'm just not sure how feasible that is.

Basically this principle/method works fine using a Rohde and Schwarz 20 GHz sig gen I have here, giving 15 dBm into a poorly tuned antenna. I can't have this here and use an expensive bit of test gear we need for other stuff, just for this though.

If I can make an oscillator that doesn't drift much and stays at 2122.4 MHz without varying out of it's 5 MHz channel bandwidth, then the simpler the better to be honest! All RF chips of this frequency seem to involve a certain amount of complexity and control for synthesis that I've found. 


Well in the good old analog days if one wanted a simple stable RF signal at a specific frequency in the microwave band they would use a simple crystal oscillator (possible with a tunable 'padding cap' to be able to tweak the freq a little) followed by a harmonic generator stage (so called multiplier class C amp stages) followed by possible higher power amp stages and lastly a good bandpass filter for the final frequency desired. This was a common requirement for building a LO (local oscillator chain) for up or down conversions.

Lefty

brightbell


I recently received Radcom the journal of the Radio Society of Great Britain for November.

There is a discussion within which describes the LMX2541, there are different versions dependant on frequency but the
specifications can be found here

http://avnetexpress.avnet.com/store/em/EMController/RF-and-Microwave/RF-ICs/PLL/_/N-100245?action=products&cat=1&catalogId=500201&cutTape=&filterButton=true&hbxSType=New Search&inStock=&langId=-1&myCatalog=&npi=&proto=&regionalStock=&rohs=&storeId=500201&term=LMX2541&topSellers=&categoryLink=true

Mention is made also of a previous article in April 2012 which discussed the LMX2470. this requires a crystal oscillator at a stable frequency or a GPS source is also suggested.  Tuning can be controlled by a PIC but I would say an Arduino would be more suitable.
These circuits are described as fractional N synthesisers which give virtually continuous tuning over a certain range.
Look them up and see if they can help you. 
The article is written by Andy Talbot G4JNT with an interesting website at http://www.g4jnt.com/.

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