Digital modulation for RF projects
LoopyByteloose
Posts: 12,537
I've got a local English language student that wants to study about RF electronics in English.
He has a masters in EE, so I thought I might jump in with all the forms of modulation and their history.
AM, FM, SSB, and the digital permutations of both that have evolved.
I am wonder how far one might be able to go with a Propeller to modulate and demodulate the digital aspect. Has anybody tried other than the digital audio (which is a perfectly valid aspect of the tropic).
I am thinking of the means of imposing a digital signal over a carrier wave with the most efficiency. It seems that one has to use zero crossing techniques to time the modulation to the carrier wave or get some nasty problems, such as harmonics and distortions.
He has a masters in EE, so I thought I might jump in with all the forms of modulation and their history.
AM, FM, SSB, and the digital permutations of both that have evolved.
I am wonder how far one might be able to go with a Propeller to modulate and demodulate the digital aspect. Has anybody tried other than the digital audio (which is a perfectly valid aspect of the tropic).
I am thinking of the means of imposing a digital signal over a carrier wave with the most efficiency. It seems that one has to use zero crossing techniques to time the modulation to the carrier wave or get some nasty problems, such as harmonics and distortions.
Comments
way above any frequency you'd modulate it with.
The important point is to band-limit the modulating signal before imposing it on that carrier, otherwise
you'd generate a lot of spurious out-of-channel or out-of-band signals. Several modulating schemes exist
from simple mixing to FM modulation of the oscillator frequency (crystal-pulling) to modern digital
synthesis driving a quadrature modulator. For the higher frequencies all of this is done at an IF before
mixing up to carrier frequency.
Includes digital modulation...Morse Code
Thanks, I may have misread something about zero crossing. The English student and I may be studying together to eventually take the FCC Amatuer Novice and Technician exams at the same. You don't have to be a US citizen to take it and there are exams every year in Asia.
I'd completely forgotten about IF. It has been a long, long time since I though about radio.
@Heater
Thanks again, that is the kind of project that may interest the student.
As it is, we had class early today and he is a bit fuzzy on modulation of any kind. So I guess we will start with AM versus FM and AM versus SSB.
I am new to digital modulation other than the basics of FSK, PWM, and a few others. I have a lot to learn along with digital conversion of audio.
It is always a bit odd to find out how narrow a techincal education can be in Taiwan. Of course, it could be he know a lot, but just has no idea of how to tal shop in English... that's my job.. to get his English up to speed. I'd be delighted if he taught me more electronics along the way.
At least I did learn Morse Code.
dit - da
da - dit - dit - dit
da - dit - da - dit
and so on. I think I can get 5 wpm going, but there is no longer any requirement to do so.
Either the ARRL manual or the one the Royal Society from Great Briton have excellent info on forms of modulation. Seams most are switching to the digital modes Quam etc. Ham radio is probably some last analog types.
I got involved with reading ARRL material as a kid of about 12 years old. Learned Morse Code for a Ham License, and even got a WWII surplus 20 meter transmitter/receiver.
Have never looked into what the U.K. and British Commonwealth nations have got going.
But then, my dad decided the neighbors would all likely get angry with it possibly interfering with their TV reception. Morse Code was a requirement to get to First Class rank in the Boy Scouts in those days, so it wasn't a complete loss. And I did manage to listen to code for practice. Eventually go into stereo and hifi instead.
It is wonderful that HAM radio is open to all ages and even to non-citizens.
BTW, the article linked to by Heater contains some erroneous info: namely, that a low-pass filter will take care of PLL jitter. It will not.
-Phil
I did wonder about that low-pass filter and PPL jitter thing.
I guess if you are only putting out a small signal far from anybody who might notice you can get away with it.
Anyway, I think our man here should start with a single tube transmitter. Where the one active device acts as audio amplifier, rf oscillator, and modulator!
It would be extremely interesting if all these variations could be explored on a Propeller or Propeller 2... very educational.
http://electronicdesign.com/communications/understanding-modern-digital-modulation-techniques
There's a copyright notice at the bottom of the webpage you scraped and posted here as a PDF. I would recommend deleting the attachment and just post a link to the webpage itself.
-Phil
The link is right in the top of the PDF document anyway. I have just gotten in the habit of printing PDFs for web pages to be read off-line.
Yeah, I somewhat expected that the demodulation would be more demanding. But one does have to understand first what they are trying to demodulate... and so... it seems obvious that the study of both starts with modulation.
For what it is worth, AM modulation is still very valid, along with its power frugal offspring .. Single Side Band. If you are just starting with AM, get a Novice HAM License and move on to Single Side Band. It might take 2000 watts of AM to reach Taiwan, but only 250 watts of SSB to do it.
FM modulation is important too, less noise - but line-of-sight transmissions. Good for cellular phones, wifi, and other short distance applications.
And of course we have added a third to the mix, Phase Modulation. That's where digital jumps on board.
From there it appears that everything is a mix of those three in ways that can cram for binary date into tighter bandwidth and lower power. It is all quite amazing.
-Phil
On the one hand it has been said that: "Digital designers are actually RF engineers but they don't know it". That is to say that digital designers work with zeros and ones but when it comes to actual physical circuits they are dealing with edges that require attention to giga hertz analog technology.
On the other hand, we have "digital" modulation schemes like QAM which are dealing with multiple signal levels and phases. This is not any kind of normal "digital" thinking.
Turns out that because of this engineers who understand analog and RF are in short supply and great demand.
It seems to be a leading edge to me. Obviously, hybridization of analog and digital does get more into a tigher bandwidth and at lower power. The guys that are working with 4G and 5G (next generation) networking are breaking new ground and it is fun to try to keep up with what they are doing.
Basically my English student hopes to move forward rather than just remain in a routine job in one of Taiwan's chip foundaries.
You have AM, amplitude modulation, FM, frequency modulation, and PM, phase modulation. (I & Q signal for color television).
The intelligence (data or voice) that is sent through these mediums can have ad infinitum modulation processes. I did find that someone
had used an HP calculator for digital transmission. Just like computer protocols (similar) you can identify signals in a similar way.
There is alot of software to help on this, and computers can be used as radios to intercept signals and process. I do not know if
anyone has used the propeller for this purpose. The true digital radio needs a network to be processed on;very different from
the analog repeater. You can do ALOT of functions with the digital radio, than just talk and send data.
I think that analog and RF engineers who can do CMOS design are in high demand. At the company where I work many of them do have PhDs though, so perhaps the screening process is quite difficult.
Here's a few years old article discussing the shortage - I remember seeing others but I couldn't find them.
http://www.mercurynews.com/ci_18711322
Troubleshoot to the board level?
Not component?
Infinite.
But, still, really - "infinite"?