Oscillator design (High speed)  - Page 1
Forum section: electronics / rf-microwave

author: Rickpercy87
author_rank: Contributor
timestamp: July 13, 2016, 10:22:35 pm
content: Hello I'm looking to make an oscillator which can sweep between 1.5 and 1.6ghz.Some of you may be aware this is in the GPS frequency. You are correct.I'd like to make a small jammer (I'm aware these are illegal in many countries) but will not be used maliciously.Im simply curious.I've made some oscillators before using 555 timers and wien bridge (albeit simple designs), but the frequency is nowhere near what I need.What is the standard for designing circuits capable of high frequency including those in the microwave bands?Thank you

author: tggzzz
author_rank: Super Contributor
timestamp: July 13, 2016, 11:01:25 pm
content: Quote from: Rickpercy87 on July 13, 2016, 10:22:35 pmEven if not malicious, such a device can be lethal.A friend of mine relates the tale where his GPS said he was above a (military) runway. He wasn't; he could see it was a approx a mile away. Now use your imagination.

author: uncle_bob
author_rank: Unknown
timestamp: July 14, 2016, 12:51:25 am
content: HiWell, having had gear we make taken off the air by GPS jamming in the UK ... sorry ... not something that seems like a really good area to investigate.Bob

author: StillTrying
author_rank: Super Contributor
timestamp: July 14, 2016, 03:20:07 am
content: The US Military have used this type of stuff, and they own the gps satellites system, so have you tried dropping them an email. They might even offer to pop roundwith some of their surplus equipmentfor you.

author: qn1993
author_rank: Newbie
timestamp: July 14, 2016, 03:34:29 am
content: Hi,In my opinion, there is no short and easy way to get your jammer up and running, no matter how small it is. The reasons are:- RF and high speed (>= 1MHz) circuit behave in a different way compare to "low speed" circuit. At such extreme frequencies, things like skin effect and reflection become serious and need special design. Those techniques are not usually well understood.- To overcome such challenges, RF engineers need to have access to special equipment (vector network analyser, precision frequency counter with atomic or GPS-disciplined clock, spectrum analyser, field solver and special simulation software). I don't think that the general public have those "weapons" available to them.If you still insist that you want it (which is the right attitude when you face any problem), may I suggest:- 1st: get the oscillator running on a single frequency only. Wide band design adds one more level of complexity over on something that is tough enough. A crystal plus a clock generator (like Silicon Labs any frequency in any frequency out IC) should do the trick.- 2nd: OK, suppose you have a 2.5GHz sine wave already. You need to emit it out with enough power, which mean you need an antenna and a driving circuit. There are many reference meandered antenna design out there, you should be able to grab one. The driving circuit can be a RF driver like ADL5321. Also, do pay attention on impedance matching. If you don't understand how to do it, nothing will work.- 3rd: power mangement. Seem silly, but RF circuit have special demands towards power supply circuit.- 4th: there will still be a lot of traps. Most consumer passive components aren't suitable for RF circuit. FR4 based PCB starts to become lossy at 2 GHz so be careful.- 4th: whatever you do, be sure not to affect anyone else other than you. I don't want ot be your partner in crimeHope this helps.Quang.

author: grouchobyte
author_rank: Regular Contributor
timestamp: July 14, 2016, 04:31:48 am
content: Quote from: Rickpercy87 on July 13, 2016, 10:22:35 pmEasy......Google microstrip oscillator. Been there, done that. 6 Ghz is pushing FR4-08 but 1.6 G is a piece of cake. You might need Rogers or Arlon dielectrics at those scarier (2GHz and above) frequencies to keep losses minimized. Its fun, enjoy!. I used spice to model this design, believe it or not@grouchobyte

author: rfbroadband
author_rank: Unknown
timestamp: July 31, 2016, 01:53:54 am
content: I would start by simulating a single transistor oscillator, but if you are new to discrete RF design you need to come up a learning curve (what simulator to use, models..etc).If you just want to prototype it the question is how to you verify the performance and what kind of equipment do you have?If it oscillates it is easy to verify freq. and tuning range with a spectrum analyzer or a very fast scope.If it does not...how do you debug it, you will have to break the feedback loop and use a VNA for loop measurements, or as I said you should try to simulate it first. Especially if you are new to this, you will learn a lot if you simulate the circuit first, even if the measurements don't match the sim completely.To get you started I attached an NXP appnote that describes a 1GHz discrete VCO design using the BFR92A. This will get you started.

author: German_EE
author_rank: Super Contributor
timestamp: July 31, 2016, 08:43:17 am
content: Could I design this, yesCould I build this, yesCould I tell you how to build this, yes, but I'm not going to. What you're doing is illegal and it means that everything from the local taxi to the ambulance service won't be able to use their GPS systems when they are near your jammer. I like my liberty and I like having a ham radio licence, so I'm not going to lose either of them by aiding you in this illegal exercise.You want to break the law and possibly put lives in danger because you're curious, dumb!