RF Basics - Page 1
Forum section: electronics / general

author: Vasiliy
author_rank: Newbie
timestamp: April 07, 2012, 08:55:10 pm
content: Hi Dave.I'm working on RF students project right now. The start was very difficult - RF topic is almost completely ignored at my university. We had a luck of having a few experienced RF engineers to consult with, and it turned out that a few very basic advices can save you hours of work and reading.I'm sure that it will help many beginners if you will do an overview of RF basics. When I say "basics" I don't mean Maxwell's equations and modulation schemes, but transmitting/receiving system architecture, transistors and other building blocks, and the electronic issues involved.ThanksP.S. An advanced overview will also be appreciated

author: slateraptor
author_rank: Frequent Contributor
timestamp: April 08, 2012, 05:47:27 am
content: Quote from: Vasiliy on April 07, 2012, 08:55:10 pmThe average RF engineer invests countless hours of dedicated study at the graduate level and even more time in industry to attain the specific knowledge that you seek in minute detail.

author: Rerouter
author_rank: Super Contributor
timestamp: April 08, 2012, 05:50:42 am
content: what i fear is becoming a catch phrase of mine, pick a starting point and then decide from there where you wish to spreadRF has many different areas, skiilsets and techniques, even based upon the frequencies, a project working at 60Mhz is going to be drastically different to one working at 5Ghz

author: Zad
author_rank: Super Contributor
timestamp: April 08, 2012, 03:00:18 pm
content: Amateur radio is the place to start. I don't think I have seen any ham books which even mention Maxwell's equations. As you can imagine, they are very much orientated towards the practical side of things (sometimes a bit too much so) but there are some great books out there.Ideally, I would find an amateur radio group which has some of the ARRL publications that they can at least show you, so you can judge your level and area of interest. They ave books which start at a very basic level and go on to some very obscure and esoteric subjects indeed.The ARRL handbook has a huge amount of content, but isn't a tutorial:http://www.arrl.org/arrl-handbook-2012This is a bit more theory-orientedhttp://www.arrl.org/shop/RSGB-Radio-Communication-Handbook/Have a browse anyway.

author: djsb
author_rank: Super Contributor
timestamp: April 08, 2012, 03:19:38 pm
content: Here's a link on Manhattan style prototypinghttp://www.cliftonlaboratories.com/Prototyping.htm#Manhattan_Construction_for_RFAs always the best way of learning is by building thingsThis post (by me) may be of interesthttps://www.eevblog.com/forum/projects-designs-and-technical-stuff/40-uses-for-germanium-diodes/RF is a bit of a specialized subject but no harm in giving it a try.I may be doing the same over the summer as I have an FM tuner project I want to start.David.

author: ejeffrey
author_rank: Super Contributor
timestamp: April 08, 2012, 06:45:45 pm
content: Quote from: slateraptor on April 08, 2012, 05:47:27 amThe average digital electronics design engineer invests countless hours of study and practice to attain mastery over their art. It doesn't mean there aren't simple things that can be done by non-experts, or that there is no way to get started.

author: wkb
author_rank: Super Contributor
timestamp: April 09, 2012, 08:50:22 am
content: Quote from: ejeffrey on April 08, 2012, 06:45:45 pmAnd until we invent an "experience pill" nothing is going to change that fundamental fact of life

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: April 19, 2012, 02:01:33 pm
content: I am a relatively new ham operator [ about 4 yrs ] and have always gotten into repair / building in every hobby that I played with .And this is one of the issues I have , very little sources of learning , at least in a environment where there is 2 way interactions / Q & A , and ham radio is all about 2 way communicating .Ham radio used to be a lot of building repair , now the term appliance drive is used .Most training that I have heard of is just board replacement .And most of the hams that could help are old enough to be dyeing off .I wish I would have gotten into ham back in the 60s when I was given a Heathkit catalog , now its a lot of catch-up , and at almost 59 its getting tougher to learn and the eyes are fighting with everything getting smaller .I do surface-mount repair .If I had kids and wanted to try to motivate them into sciences / math / electronics , I think ham radio is a good motivator for that , but only if there make-up fits that interests , pushing kids into things , is a hole other subject .

author: sacherjj
author_rank: Frequent Contributor
timestamp: April 19, 2012, 03:17:09 pm
content: I would echo the HAM Radio side of things. Also, QRP radio is where you will find home built, experimenter types. This is low power (under 5W generally). GQRP club in England has a great magazine SPRAT. You can get the archives on CD, which have all kinds of great little projects that the members have contributed.As much asThe Art of Electronicsis to general electronics,Experimental Methods in RF Designis for radio. I've learned so much, just reading through this book. It has real practical circuits that illustrate topics covered. Just a great resource.Amazon Link:http://www.amazon.com/Experimental-Methods-Design-Wes-Hayward/dp/087259923X/ref=sr_1_1?ie=UTF8&qid=1334848590&sr=8-1

author: G7PSK
author_rank: Super Contributor
timestamp: May 07, 2012, 05:28:33 pm
content: Ham radio is certainly the way to go if you want to learn about RF. Join a local club they have meeting's and lectures where you can mix with and talk to other people who have the same interest and there is almost always a member who is willing to tutor you in the subject. An awful lot of modern electronics are based on developments by Ham's

author: SeanB
author_rank: Super Contributor
timestamp: May 07, 2012, 06:32:25 pm
content: G7PSK, I have started that.

author: vxp036000
author_rank: Regular Contributor
timestamp: May 12, 2012, 11:11:38 pm
content: A few of the previous posts have summed it up nicely. What you're trying to learn is what most folks spend 4 years in graduate school studying. Having said that, there are numerous schematics online for basic receiver and transmitters. A transmitter can be nothing more complex than a VCO with a buffer and power amplier stage. You may need to worry about impedance matching, depending what frequency and what kind of power levels you're working with. For the receiver, an RF amplifier followed by a peak detector may suffice, unless you need relatively high sensitivity. But I really do suggest picking up a book on RF system design, there is much more to it than what you can pick up from a few websites.

author: Vasiliy
author_rank: Newbie
timestamp: June 19, 2012, 10:29:03 am
content: Thanks to everyone for your replies.I don't understand the attitude of some folks here: "It takes hours and no one can help you in five minutes. Keep struggling!". I agree that it takes hours, but I don't see any reason not to help with very basic overview. I think this is exactly what Dave does - takes a complex subject and overviews it briefly.I remember myself reading through datasheets and trying to figure out which of these parameters actually relevant to me. I remember burned transistors in Class A power amp, and hours spent to make it work. I remember the engineer, who showed me a very nice class D driver which comes in SMD package and does the work for a few dollars.It is no harm in giving the very basic. Most of people don't need more than that. For others, it will save hours in figuring out where to start and what to use.And yes, it will always take time and experimental work to become a professional.Regards

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: July 14, 2012, 09:58:03 am
content: Quote from: Vasiliy on April 07, 2012, 08:55:10 pmVasiliy,Agree with all the above posters about seeking ham radio and QRP stuff for the basics. Though there are exceptions, amateurs are most interested in narrow bandwidths and efficient modes for long distance low power communication with random stations. So there'll be more stuff on Morse code and analogue voice modes than (say) broadband time synchronised point to point data links. Nothing wrong with this but note this bias.A long-term projects is coming up with a series of RF building blocks that can be assembled to form various transmitting and receiving projects. In thinking about this, I've come to the realisation that just four basic modules are required to construct a huge range of transmitting and receiving equipment. In their simplest form each module can be built with just one active device and no more than 10 other parts.The basic stages of analogue RF are:Oscillators.Role is to generate an RF signal for amplification or mixing. Done with transistors or ICs. Require a frequency determining element, such as a quartz crystal or L C tuned circuit.Amplifiers.May be at audio or RF. Role is to increase strength of a signal. Done with transistors or ICs. If their output it tuned right then amplifiers can multiply frequencies as well.Mixers.Role is to take two incoming signals and produce a sum and difference (only one of which is normally desired). Depending on position in a circuit it may be (i) to mix audio with RF to produce an RF output, (ii) to mix RF with RF to produce an RF output on another frequency, or (iii) to mix RF with RF to produce an audio signal. Can be done with diodes, transistors or ICs.Filters.Role is to select out wanted from unwanted frequencies. Can be high pass, low pass or band pass depending on how inductors and capacitors are connected. Either passive (coils and capacitors only) for RF or active (needs transistors or op-amps) for audio.In between stages you may have impedance matching, usually some sort of transformer, matching network or transistor stage.Everything RF is a combination of of the above.Build 2 or 3 of each stage and you have a whole communications system if they're put together right.Eg an oscillator on its own is a transmitter, but it won't be strong enough to transmit a useful distance unless it's followed by an RF amplifier. It won't transmit anything intelligent unless it is somehow modulated with voice or data. For that you'll probably need a mixer stage between the oscillator and amplifier. To keep the output clean you'll need one or more filters in various parts of the circuit, but especially after the last RF amplifier. In other words a basic transmitter can be done with 1 stage but 4 or 5 makes it much more useful.And to pick it up you'll need to do exactly the reverse. Convert the incoming RF down to audio. Any form of conversion needs a mixer. A mixer needs something to mix with so you need an oscillator to give the mixer a signal to beat the incoming signal (that comes to it via the antenna) with. As it happens one output of the mixer is at audio frequency, but is extremely weak. So add an amplifier to boost it to be heard/decoded. The signal from your transmitter isn't the only one around, so to prevent interference you'll need at least one RF filter. There's various places in the receiver to have them but in the antenna line is an OK place.The above sounds more complex than it actually is. Some jobs required above can be done with just two or three parts. Some tasks (eg filtering) even require no parts if you go the software defined radio route. If you combine a transmitter and receiver in the one box some stages can even be used in both lessening parts count.Below are descriptions and demonstrations of simple RF gear capable of transmission and reception from a few hundred metres to thousands of kilometres:Basic HF receiver:Basic HF receiver (more discrete parts):Basic VHF FM receiver:Basic HF morse transceiver:Basic FM voice VHF transmitter:Basic SSB voice HF transceiver:Some have circuits at the end or useful links to the same or similar circuits.Key design challenges include:Transmitter frequency stability:Free-running oscillators can be difficult to get stable enough. Crystals are stable but you often want agility. Synthesisers can be stable but have a less pure output and are more complex.Transmitter output cleanliness:Amplifier stages must not self-oscillate and self-destruct, even when presented with odd antenna impedances. Harmonics and unwanted mixer products should be adequately filtered. RF feedback should be prevented by sufficient shielding, bypassing and short leads. With some modes amplifiers need to be linear (not class C) to avoid distortion.Transmitter power output:More power means more stages, more bulk, more power consumption. TThere may be a point of diminishing returns (above about 20 watts on HF) where more power isn't worth the effort, especially for portable equipment.Choice of transmit mode:Some modes are more complex to build but are more efficient (eg SSB). Others are simple to build transmitters for, sound really good but are harder to build receivers for and take more bandwidth (eg FM). Some digital modes require extremely high frequency stability (WSPR). Morse gets though well under poor conditions and is simple to build equipment for but is not everyone's taste.Receiver sensitivity:Must be sufficient gain to hear background noise when an antenna is connected.Receiver selectivity:Filtering must be enough to prevent other signals from interfering with desired signal.Recever strong signal performance:Amplifier stages must be strong enough to not be overloaded with strong signals. A problem though is that receivers with 'strong' front ends draw more current, which is undesirable for portable battery operation.Receiver images:If using RF frequency mixing, as with a superhet receiver, intermediate frequencies need to be chosen to avoid spurious responses and images. In direct conversion receivers the 'audio image' is an inherent problem unless the circuit is made more complex.Multiband operation:The complexity of an RF project rises exponentially with the number of bands it must cover. But it's good having several bands so that contacts can be made under different radio conditions.Antennas and feedlines are other story, but for all but except for specialised applications two quarter wavelength long pieces of wire or rod will work fine.I suggest reading the Talking Electronics stuff and build their FM bugs (this will help with all above stages except mixers). Then look at QRP transmitter and receiver circuits including the Experimental Methods of RF Design book, which is probably the best available reference.Peter