Radio from first principles ? - Page 1
Forum section: electronics / rf-microwave

author: jwhitmore
author_rank: Regular Contributor
timestamp: May 13, 2016, 09:28:21 pm
content: I probably need a good book rather then pestering you people. I'm starting out and I could get into HAM radio by spending money on an expensive radio and all the gear. I'm afraid I'd learn very little that way so I want to do it from first principals. Almost follow the evolution of Radio so to speak. Most books seem to be at a higher level then that. Like getting an SDR up and running. I'll get there eventually I hope.So I'd like to put up a self build antenna and just plug it into my Rigol 1054Z and be able to understand what I'm looking at. Then go from there amplify and filter and all that stuff.So my question would be book recommendation and what "bandwidth" antenna should I start with. I assume Morse in the 20M band and stretch a piece of copper wire out across the lawn or something?

author: MrSlack
author_rank: Frequent Contributor
timestamp: May 13, 2016, 09:51:01 pm
content: It's a little more complicated than that but not much.A good book - yes, but I suspect we're fine being pesteredI'd suggest grabbing a copy of the ARRL Handbook which is published yearly (mine is 1995 - old ones are fine). It's chock full of the fundamentals of radio. Digest some of that before you look at the signals on a random wire antenna.You can do exactly what you have described but a time domain instrument like a scope isn't really very good for looking at what comes in on the wire. You need to at the very least stuff it through a resonant filter and detector/demodulator, resulting in a "crystal set" and observing the reuslt of that. You can build one of these with a schottky diode, a variable capacitor and a coil of wire. Then stick an LM386 AF amp on it. That will be far more useful than a scope for early experimentation.A scope is going to do the majority of its work if you move to a direct conversion or superhet receiver.40m CW (morse) seems to be the easiest place to pick anything up reliably but you will need to use a BFO (beat frequency oscillator) with a crystal set to actually hear any CW as the carrier is modulated on and off which has no audio component. On this basis I'd try and build a shortwave broadcast receiver which uses AM modulation and works fine on a crystal set. You can then bodge it with a BFO later (most of RF is progressive bodging I find)

author: hendorog
author_rank: Super Contributor
timestamp: May 14, 2016, 02:57:51 am
content: An easy way to start might be to use the HAM exam training material - e.g. for NZ it is here:http://www.nzart.org.nz/assets/exam/Study_Book_14022013_Teachers_Edition.pdfSection 15 (Page 90) onwards is where it talks about how transmitters work, antennas etc.You should be able to get a quick overview of what is involved, what you already understand and what you need to learn about. Then go and find more detailed info on the bits you are missing.

author: uncle_bob
author_rank: Unknown
timestamp: May 14, 2016, 03:48:20 am
content: HiWell, a lot depends on just how "first principles" you want to get. Physics is a good starting point for a lot of the basics of radio ...That said, I think you would have a lot more fun doing it with some of the stuff targeted at Ham radio. The basic stuff for a license course is not a bad way to get the introductory stuff.Bob

author: mtdoc
author_rank: Super Contributor
timestamp: May 14, 2016, 03:58:10 am
content: I bought but have not yet readBuild Your Own Transistor Radios.It gets good reviews and the author, Ronald Quan is a bonafide ex-HP analog guru. He wasinterviewed on the AmpHoura while back.

author: AF6LJ
author_rank: Unknown
timestamp: May 14, 2016, 04:26:02 am
content: Quote from: jwhitmore on May 13, 2016, 09:28:21 pmAntennas are wideband by nature.Please elaborate on what you mean by wanting to do it from first principals, I don't quite grasp what you mean.Learning the code is a good thing, many still use it and a few are very well into that mode of transmission.

author: Martin.M
author_rank: Frequent Contributor
timestamp: May 14, 2016, 07:07:24 am
content: first principals of radio transmission are to homebrew by a doorbell (the interruptor provides a signal what is useful for short distance as TX) ,,and a detector radio simply made by a wire as antenna, a coil with C and germanium diode, following a high impedance headphone for listening.the lowest stage of radio is the detector.the next a detector with audio amplification,the next a Regen or Super Regen radio, with Tube, oder Fet,the next a Regen with pre amplification stage,the next a superhet (this are the most of all home radios)the master is a double / triple conversion superhet (the big ear)Coils are to wind self by hand.There is some low expensive test equipment required, at best a HF signal generator with a trustful scale.greetingsMartin

author: voltz
author_rank: Frequent Contributor
timestamp: May 14, 2016, 10:40:44 am
content: If you plug a length of wire into your scope, you wont see anything of any great interest. Mainly just 50/60Hz mains hum with local noise mixed in. Thats coming from power lines near by and devices in people homes.A much better device to plug it in to would be a spectrum analyser. Then you get to see frequency spikes of radio signals being transmitted. Thats more interesting because you would see carrier levels and what frequencies they are at. Its giving you a window on what the length of wire - antenna - can see. In practice, those signals would appear small unless you used a premap. We're talking micro volts here for example S9 on a radio is 50 micro volts rms. And anything down to 0.2uV for really weak stations.Hf SDR boxes can show similar information with their panadapter style waterfalls and peaks. So a cheap SDR box that works on HF would be a nice introduction to understanding frequency and amplitude of carriers on the bands. A nice place to check out would be say the 40m band in the evenings. Its pretty much long distance most of the time. 20m during the daytime.Once you get a feel for radio signals and viewing a spectrum display, you're ready to start building simple oscillators and then see them appear on your display as a carrier. You can then play with adjusting its frequency and amplitude and boom! you just made a super simple CW transmitter if you turn the power on and off (a very crude method but demonstrates the principle).Some stations working QRP can actually be heard hundreds even thousands of miles away using nothing more than a crystal oscillator and long wire.Receiving signals and demodulating them is a little harder. And that would be the next step. Many books and designs for simple receivers. But of course a simple SDR box and PC would do that nicely.That would be my 'first principles' or probably a better word, 'introduction' to understanding radio. Other opinions may vary.Good luck, and more importantly, have fun with it. Ham radio is meant to be fun and we like to experiment with it.

author: KM4FER
author_rank: Regular Contributor
timestamp: May 14, 2016, 02:40:59 pm
content: Here's the way I did what you are wanting to do, all from parts in my junk box and bits and pieces of information from the internet.Of course I did absolutely everything wrong for RF; long leads, no ground plane, no sheilding, piece of wire for antenna. But it works and that is all I was trying to accomplish.This is just a simple direct conversion receiver that converts a range of RF frequencies down to audio frequencies. These audio frequencies are then fed into the mic input of my computer. A program called HDSDR then converts the signals into various forms for display and audio to the speaker. Here's a screen capture of signals in the 40 meter amateur band. The dashed vertical lines in the upper window are CW Morse code. There happened to be a contest going on when I did the screen capture so there was a lot of activity.Now I'm starting over to correct all the things I did wrong and make other improvements as well. Still in the planning stage.Go for it. Have fun.KM4FER

author: MrSlack
author_rank: Frequent Contributor
timestamp: May 14, 2016, 03:38:32 pm
content: That is beautiful in it's own way - if it works, who caresAlso if you're lazy like me, hithttp://websdr.org/

author: saturation
author_rank: Super Contributor
timestamp: May 14, 2016, 06:56:23 pm
content: For first principles, you want a crystal radio as receiver and transmitter as a spark gap.https://en.wikipedia.org/wiki/Crystal_radiohttps://en.wikipedia.org/wiki/Spark-gap_transmitterThen you gradually build by tuning i.e., resonating, then amplification, oscillators etc.,Much of these are made as science kits in toy stores.

author: jwhitmore
author_rank: Regular Contributor
timestamp: May 23, 2016, 02:40:48 pm
content: Apologies for the tardiness of my reply and thanks so much for all your help. I'm getting there and will be trying my hand a a few simple circuits. I looked into the half wave length antenna and it makes sense to me now. Looking into it this time I see that it's made of two 1/4 lengths with a gap in the middle and the current flow between the gap is the input to the receiver.One problem I have is with this is when it becomes a transmitter. If you use the analogy, often used, of a pipe full of water for electricity. In a sealed pipe if you move it about in gravity I can imagine that water molecules will move about a little, so if you could detect this minute change at the centre of the pipe you could possibly determine its angle to the horizontal. If you now reverse that and connect a water source to a sealed pipe turning on and off the tap doesn't do much. Similarly if you connect the transmitter to the antenna even if you increase the voltage there ain't a lot of current flow in an open circuit.What can I say I'm used to charge flowing from DC +ve to -ve anything else is heresy. (Yes AC is Heresy) Still one step at a time. First a half wave length antenna and a circuit.thanks a million again for all your help

author: KM4FER
author_rank: Regular Contributor
timestamp: May 23, 2016, 03:59:30 pm
content: Try thinking of an antenna not as a sealed pipe but like a garden soaker hose, one of those with lots of tiny holes that let water escape. You pump some electrical energy into the antenna and some escapes in the form of electromagnetic waves.Earl...

author: MrSlack
author_rank: Frequent Contributor
timestamp: May 23, 2016, 04:47:32 pm
content: Best explanation if a little math heavy:http://www.feynmanlectures.caltech.edu/II_01.html

author: tggzzz
author_rank: Super Contributor
timestamp: May 23, 2016, 05:37:18 pm
content: Radio from "first principles" really means starting with Maxwell's equations and building up from there. You will be on your way to nirvana when you understand why earth/ground is a fiction, and the relationships between div, grad and curl.As Einstein(?) put it. Imagine that the transmitter is the tail of a cat in New York, and the receiver is the head of the cat in San Francisco, and if you pull on the tail, the head emits a noise. Except there is no cat.

author: MrSlack
author_rank: Frequent Contributor
timestamp: May 23, 2016, 06:08:56 pm
content: Ugh vector calculus. It's been early 20 years and I still haven't recovered from that.

author: Richard Head
author_rank: Frequent Contributor
timestamp: May 23, 2016, 06:24:38 pm
content: A beer to the first person who can still proves Stokes theorem.

author: MrSlack
author_rank: Frequent Contributor
timestamp: May 23, 2016, 06:46:58 pm
content: I'd rather buy my own beer

author: Richard Head
author_rank: Frequent Contributor
timestamp: May 24, 2016, 05:43:27 am
content: Me too!

author: German_EE
author_rank: Super Contributor
timestamp: May 29, 2016, 09:18:55 am
content: OK, the first principles of radio:You see, wire telegraphy is a kind of a very, very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? And radio operates exactly the same way: you send signals here, they receive them there. The only difference is that there is no cat.Albert Einstein 1879 - 1955