Signal division - Page 1
Forum section: electronics / rf-microwave

author: Blade87
author_rank: Contributor
timestamp: December 21, 2018, 01:44:29 pm
content: Hello everyone,I want to know what is the method to divide an analog signal in frequency domain? Let's say I have an arbitrary 100 MHz signal and I want to divide its frequency by 10 and I want to have exact waveform in lower frequency. I read about Miller frequency divider but I have some problem with it,First, I didn't find any circuit representation of it.Second, It can divide a signal by 2.I also saw HMC983 from Analog Devices. My RF knowledge is not good, so I didn't understand does this chip do the job or not.Does anyone know a method, circuit or any additional info about how to divide an analog signal except using DSP, FPGA or digital methods? Where can I find more info about analog frequency division?

author: PA0PBZ
author_rank: Super Contributor
timestamp: December 21, 2018, 03:31:12 pm
content: Why do you want to divide? If it is just to bring the frequency down mixing is a proven conceptSo mix your 100MHz signal with 90MHz and there is your 10MHz signal with the exact same waveform.

author: Blade87
author_rank: Contributor
timestamp: December 21, 2018, 04:48:30 pm
content: Hi PA0PBZ,Thanks for the quick reply. Frequency mixer is not my answer. I want to map a high frequency signal to low frequency while trying to keep low frequency contents of my signal. If I mix my signal with a 90 MHz signal, the result won't have any frequency contents of original one under 90 MHz. I like to know about a frequency compression because my signal is not pure sinewave.

author: PA0PBZ
author_rank: Super Contributor
timestamp: December 21, 2018, 04:59:12 pm
content: I'm still not sure what you are trying to do but if you divide a let's say 100MHz signal by 10 you will not have any component above 10MHz left. Also, if you divide a signal by 10 you kind of throw away 9 out of 10 'samples' so you will not end up with the same waveform anyway.

author: Blade87
author_rank: Contributor
timestamp: December 21, 2018, 05:22:46 pm
content: Thanks again for your answer. My goal is to visualize a high frequency signal in my old oscilloscope. I want to see its shape. It also crosses my mind to use this method ( if there is one) to visualize even higher frequency to a lower one. In digital it looks simple but when thinking about the processor, ADC, DAC, real-time programming, ..., I think it won't be simple. Isn't there any analog method for this task? If we cascade bunch of Miller frequency divider can we compress the signal?

author: Blade87
author_rank: Contributor
timestamp: December 21, 2018, 06:41:22 pm
content: Can anyone explain about Miller Frequency divider? Is the there any way to increase the division factor? here's a block diagram I saw on Wikipedia.

author: PA0PBZ
author_rank: Super Contributor
timestamp: December 21, 2018, 06:54:31 pm
content: A miller frequency divider is nothing more than a mixer which mixes the input signal with itself, so with that you are back to downmixing.QuoteThe shape of the signal will not change by mixing it with another signal, only if you have components that are higher in frequency than the output signal of the mixer they will get lost. But your scope would not display these signals anyway. You simply can't divide a signal down to another frequency without losing information. If the signal is repetitive you could look at sampling (see sampling oscilloscope).

author: Blade87
author_rank: Contributor
timestamp: December 21, 2018, 07:17:36 pm
content: Can you introduce me a reference for better understanding? And what is the sampling oscilloscope?

author: PA0PBZ
author_rank: Super Contributor
timestamp: December 21, 2018, 07:26:19 pm
content: Quote from: Blade87 on December 21, 2018, 07:17:36 pmBetter understanding of what?QuoteBasically a scope that takes precise timed samples of the input signal so that the waveform albeit a lot faster than the scope can handle can still be reconstructed. Google it.

author: Blade87
author_rank: Contributor
timestamp: December 21, 2018, 07:43:34 pm
content: QuoteI want to know more about "mixers" . I have some old basic information about them from school. Can you point some good reference about them?QuoteWith the picture you sent I think I realized about sampling method. Thanks a lot.

author: ejeffrey
author_rank: Super Contributor
timestamp: December 21, 2018, 07:50:52 pm
content: A mixer will change the shape of the waveform although the signal content will be the same. For instance if you have a signal that is amplitude modulated at 1 MHz, the original signal will have 100 phase peaks per modulation cycle, while the down-mixed will have only 10. That is pretty easy to understand for simple modulation like this, but for arbitrary waveforms will not necessarily be obvious. You could digitally reconstruct the original by recording the waveform off of your scope and digitally emulate upconverting by 90 MHz again. As long as your signal is band limited around 100 MHz this should work, but if you want to look at a square wave this isn't going to do what you want.In general, the only way to "slow down" a signal while preserving its shape is to digitize a small segment and play it back slower. This requires basically building your own scope, so it isn't a great way to extend the performance of an existing scope.

author: PA0PBZ
author_rank: Super Contributor
timestamp: December 21, 2018, 07:51:54 pm
content: Quote from: Blade87 on December 21, 2018, 07:43:34 pmGoogle 'rf mixers'. There is so much information out there that I have no idea how to pick the ones that will help you. If you have any specific questions do not hesitate to ask them here, there's a lot of knowledge on this forum that far exceeds mine.

author: Blade87
author_rank: Contributor
timestamp: December 21, 2018, 08:21:36 pm
content: QuoteAt this time, I think I need to know more about mixer and its applications to ask a more precise question.Just in case if someone sees this post at some time in the future, I saw a good video about "mixers" from youtube channel "w2aew". This guy had a good explanation about mixer. The name of the video is " #83: Basics of RF Mixers in Radio Receivers / Mixer Tutorial / Frequency Conversion ".

author: Blade87
author_rank: Contributor
timestamp: December 21, 2018, 08:25:35 pm
content: QuoteFinally I think doing this task in digital domain could be a better approach. Thank for your answer.

author: David Hess
author_rank: Super Contributor
timestamp: December 21, 2018, 10:15:42 pm
content: Quote from: Blade87 on December 21, 2018, 05:22:46 pmA sampling front end to turn your old oscilloscope into an analog sampling oscilloscope will do exactly what you want.https://www.electronicdesign.com/boards/1-ghz-sampling-oscilloscope-front-end-easily-modifiedhttp://www.redrok.com/Circuits_1GHz-samplig-Oscilloscope-Front-End.pdf

author: Blade87
author_rank: Contributor
timestamp: December 22, 2018, 05:13:39 am
content: QuoteI really like the idea of sampling oscilloscope. I will read the pdf you sent and google about sampling oscilloscope (specially sampling oscilloscope module). Thanks for your sharing.

author: hagster
author_rank: Frequent Contributor
timestamp: December 24, 2018, 07:13:15 am
content: While all this mixing and sub-sampling does work. My general advice for looking at RF frequencies(cheaply) is to use an RTL-dongle (~$20) and GNU radio companion. It handles all the downconversion for you. If the 2MHz bandwidth is not enough there are more expensive options that perform better.

author: Blade87
author_rank: Contributor
timestamp: December 24, 2018, 10:41:51 am
content: QuoteHi hagster,Very good suggestion. I think SDR is a good cheap device that can help me.