Learning 'communications' at school, want to also learn the practical side - Page 1
Forum section: electronics / beginners

author: Sevalecan
author_rank: Newbie
timestamp: February 18, 2016, 04:59:00 am
content: The subject pretty much sums it up. I'm in an Electronic Communications class for my major and we're discussing things revolving around amplitude and frequency modulation and demodulation, as well as single and double sideband signals. I'm interested in learning how to implement these things with analog circuits, avoiding special ICs made for it as much as possible. The class and lab deals with Fourier Transforms and all the theory and math behind it, and a few 'system' diagrams made up which describe a pipeline, but there's absolutely no discussion on implementing circuits of any kind to do the operations necessary to say, modulate and demodulate a signal. I'm specifically avoiding the subject of DSPs for this purpose because it just seems too easy to plug in the math, and analog circuits are, as far as I know, cheaper and more challenging to design. I should also mention that I'm in my first of two Electronic Circuits(essentially semiconductor circuit analysis) classes. I understand the basic concepts of how BJTs and MOSFETs work, but I'm not yet familiar with the circuit models of these devices.That said, my goal here would be to construct some form of radio transmitter or receiver using discrete semiconductors as much as possible. I'm not actually sure where to start looking for information, though. Google searches lead me to textbooks that continue to discuss theory rather than application. Rather, I guess I'm looking for some sort of reference which shows common analog circuits used in this application, with some level of analysis on how they work. (It is my expectation that even after learning circuit models for more semiconductors, complicated circuits will not be something I can quickly dream up on my own, similar to my belief that I'd never come up with a fourier transform on my own, or invent calculus. If it is anyone's experience that these circuits are much simpler to create though, I'd like to know).In one type of system, we use a multiplier for both modulation and demodulation, as well as filters (which are easy enough to find), and a phase locked loop. Both the PLL and multiplier are a couple of things I'd like to start with, but I'm having difficulty finding much information on a discretely built multiplier or PLL circuit. Essentially the point of all my blabbering is: where can I get started on practical analog circuit design, I'll get all the theory I need as time goes on.Of course, feel free to tell me if I'm totally off my rocker as well with where to get started. I can take it.

author: aaronhance
author_rank: Regular Contributor
timestamp: February 18, 2016, 04:39:17 pm
content: Depending on where you are you might need a license to operate a transmitter that you have built. I have learnt recently rf laws can be very strict.Edit: this might be useful:http://electronics-diy.com/electronic_schematics.php?schematics=fm_receivers&circuit=FMhttp://electronics-diy.com/am-radio-lm555.php

author: Sevalecan
author_rank: Newbie
timestamp: February 18, 2016, 09:52:27 pm
content: Quote from: aaronhance on February 18, 2016, 04:39:17 pmThis is certainly true. For the U.S.(where I live), I think there are a few specific bands which are open for anyone to use.. Other than that, I'd either aim to keep transmitter power low to work in a range of feet or just skip transmitting over the air since my goal here is to learn about the individual circuits for modulating and demodulating a signal at the moment.QuoteThanks, I'll give these a look.

author: Unknown
author_rank: Unknown
timestamp: February 19, 2016, 10:49:59 am
content: Search on Youtube for W2AEW, he's a member of this forum and has produced some excellent quality tutorial videos including one on PLLs. Although strictly speaking you are not generally allowed to operate transmitters without a licence, if you are experimenting with low frequency and low power circuits, they won't usually radiate beyond a few feet so you will be ok. If you get really interested, see if there is a ham radio club near you.

author: Eric_the_EE
author_rank: Contributor
timestamp: March 01, 2016, 06:16:23 pm
content: I am in a very similar situation - Digital and Analog Communications course. All theory, no hands-on.To compensate, my professor assigned us a term project in addition to the course material. Our objective is to choose an area of communications we want to learn more about and research the topic in-depth until we understand it very well, from the physical layer up to the MAC layer.I am researching software-defined radio - so that is mostly digital design.If you are interested in analog design, I would really recommend diving straight into amateur radio (HAM radio) to learn the basics first. There are many practical things to learn in this hobby (I've been a licensed HAM tech for 2 years now), and you will soon be able to start connecting the dots between theory and analog circuit design.If you search "HAM radio", you'll get many avenues to examples.

author: mobbarley
author_rank: Regular Contributor
timestamp: March 01, 2016, 09:33:20 pm
content: A PC with SDR can also be an awesome tool for analysing radio equipment at a high level.

author: mojoe
author_rank: Frequent Contributor
timestamp: March 02, 2016, 05:36:12 am
content: I'm surprised no one has mentioned this yet, but just about any copy of the Radio Amateur's Handbook by the ARRL (in the US) from the past 10 years will not only have all the theory you would want, but they always have projects to build.For simple radio transmitters/receivers, look for web sites that have QRP projects. QRP means low power. You should find plenty of construction projects.Getting an Amateur license isn't hard. The Technician is the entry license and is easily obtained. The morse code (CW) was dropped years ago. With a Technician license, you have some HF privileges (some voice on 10M, the rest CW) and pretty much all privileges from 6M (50 MHz) and up. With a license, you can legally build your own gear and transmit with it. This also means that you are responsible if that gear interferes with someone, or causes other trouble.

author: tggzzz
author_rank: Super Contributor
timestamp: March 02, 2016, 08:35:55 am
content: Quote from: Sevalecan on February 18, 2016, 09:52:27 pmBeware.The non-ideal propeties ofallcomponents mean that, unless you know what you are doingandverify it, youwillalso be transmitting on other bands.To give you an inkling of you have yet to learn, make sure you know the relevance of "compression point" and "IP3" specifications, and how they influence systm behaviour.Don't be put off (but don't be a exemplar of the Dunning-Kruger effect either).

author: coppice
author_rank: Super Contributor
timestamp: March 02, 2016, 09:00:30 am
content: Any decent comms book should teach you about traditional analogue techniques for AM and FM modulation and demodulation. They don't involve the use of a multiplier. Analogue multipliers are rather clunky, and not necessary. They may use a PLL, but nobody ever implemented those discretely. The use of PLLs didn't take off until it was practical to make them in IC form (e.g. the NE56x series of PLL devices from Signetics, around 1970).

author: Cerebus
author_rank: Super Contributor
timestamp: March 07, 2016, 06:11:53 pm
content: Quote from: mojoe on March 02, 2016, 05:36:12 amI'm sorry if this seems to be Yank bashing but you guys can be surprisingly parochial for folks living in such a big country. What you're saying is specific to the US but, as Americans often do, you fail to qualify it as US specific information. The requirements for Amateur radio licences, ease of acquisition and permitted usages vary massively around the world. The names used for classes of licence are highly variable too, for instance the UK rough equivalent of the US technician licence is called the foundation licence.If the OP volunteers what country he's from I'm sure a knowledgable Ham will pipe up with that country's requirements.

author: ade
author_rank: Unknown
timestamp: March 07, 2016, 09:48:20 pm
content: QuoteThe OP is from Michigan... says so right on his/her profile...