Hi,

I've been interested in radio for a few years but every time I try to research the technicalities of everything I get a bit baffled. I understand that a transmitter is used to broadcast - but as far as the electronics, and what's going on under the hood of a transmitter, I don't know my arse from my elbow. Then antennas. Filters and limiters (similar concepts to music production?). What else is necessary.

Could anyone point me in the direction of some books, sites or videos that explain things from a pretty novice level.

Cheers

Couple other things I thought I may as well put here.. What is an amp used for in broadcasting terms - is this to amplify the watt output of the transmitter? If so, why not use a higher watt transmitter?

There are quite a few other questions and uncertainties I have so again, if there any books/handbooks (hard or digital) that someone could recommend it would be highly appreciated.

Thanks

Amp is short for amplifier. Transmitter starts with oscillator which is miliwatts. It broadcasts meters away from it. Everything after oscillator are amplifiers. Usually, you amplify oscillator to few watts in couple of stages and match output to 50ohm impedance. This is usually called exciter. After it, you go with high power amplifier (a.k.a. AMP) which get 'excited' with exciter and on its output you have high power signal.

Regarding books, google is your first choice. Just add pdf at the end of search string. Also, you can always ask questions here


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Hello Mr Pidworth!
Ive had 20 years of experience with electronics, and i still know nothing! lol
I hate to burst your bubble? but if you have no experience whatsoever with electronics? RF is a bad place to start!

Anyways as Mr Pjeva says, the oscillator is the fundamental part of a transmitter!
The circuit shown is a common Colpitts oscillator! L1,C1 and C2 form a tuned resonant circuit!
The values of L and C will determine the frequency of operation (eg 100mhz)
On its own? it wont do much! It needs feedback to nudge it into an unstable state (oscillation)
This is achieved by feeding a charge into the gate of TR1 and feeding back to the resonant circuit (LC)
via the source of TR1! (like a loop)
Then amplifier stages can be added to either improve gain? or match impedance? (buffer)

Read the second pdf from here, thats how i got started....

https://libcom.org/library/radio-my-bom ... al-pirates

Legendary book

Thanks for the replies. That pdf looks like it will be an interesting read, cheers! As for googling for other books.. I've stumbled across a few antenna books - would they be worth a look? also, some of the ham radio ones - would the info in them translate to fm at all?

sinus trouble wrote: I hate to burst your bubble? but if you have no experience whatsoever with electronics? RF is a bad place to start!

I know what you mean, but it's what I'm interested in so I was thinking it would be better to try and gain some understanding of what's going on. I was hoping to try and get to grips with the inner workings of a simple transmitter, then look to more complicated ones if/when I start to understand them.

Pidworth wrote:Thanks for the replies. That pdf looks like it will be an interesting read, cheers! As for googling for other books.. I've stumbled across a few antenna books - would they be worth a look? also, some of the ham radio ones - would the info in them translate to fm at all?

sinus trouble wrote: I hate to burst your bubble? but if you have no experience whatsoever with electronics? RF is a bad place to start!

I know what you mean, but it's what I'm interested in so I was thinking it would be better to try and gain some understanding of what's going on. I was hoping to try and get to grips with the inner workings of a simple transmitter, then look to more complicated ones if/when I start to understand them.

Yes of course, most VHF and UHF ham radio uses narrow FM. As for antennas there's lots of 70mhz (4 meter band) antennas which will work on the FM broadcast band with slightly different measurements. I'd definitely have a look around....

sinus trouble wrote: I hate to burst your bubble? but if you have no experience whatsoever with electronics? RF is a bad place to start!

Could not agree more.

I hate to discourage you, but you would really do well to have a good, general understanding of electronics as a foundation before trying to understand RF, as RF is far more complicated than general electronics. In the field of RF, things don't always work as you'd expect them to and don't either simply work or not work like DC electronics tend to - most DC electronics either work, don't work at all or blow up, in which case it hasn't worked.

There are probably three different ways to go, which I see as the following:
There's buying gear from people and plugging it in, with cable A and cable B etc. that someone supplies - understanding the terminology is about as far as you need to go.
There's building equipment from schematics and seeing if it works or not, with perhaps a basic understanding of principles.
Then there's designing the equipment and developing the design into something more efficient or more stable or lower cost etc.

Which do you want to do? This will dictate how much you need to know and where you need to start.

Pidworth wrote: I know what you mean, but it's what I'm interested in so I was thinking it would be better to try and gain some understanding of what's going on. I was hoping to try and get to grips with the inner workings of a simple transmitter, then look to more complicated ones if/when I start to understand them.

Just for reference, a "simple" transmitter is well out of context of what most people will refer to on this forum. Such a device is what we try to avoid as it ultimately causes a nuisance and hence complaints. Complaints mean that we get taken off air.

There are a few fundamentals that you need to have a firm grasp of before attempting to understand how a transmitter works. Do you understand the concept of the frequency domain and orders of magnitude, i.e. kHz MHz, GHz? Do you know how an oscillator works? Do you know how an audio amplifier works? Do you know how transformers (mains or otherwise) work? Do you know how crossovers (active or passive) work? This is all relevant - I'm not trying to pick holes. Answer honestly and I'll try my best to provide either answers or links to get you to the end result you are after.

Ah ok, perhaps I was being unrealistic then. I'm at the first of the options you said, though would like to at least get to the second. I think having a kit and following the steps would be kinda pointless if I don't at least have some idea why I'm doing things.

Sounds like I was thinking of going about things the wrong way then. Frequency domain and orders of magnitude I get. Is an oscillator in this setting doing a similar job as when used in a synth? I get how an amplifier works... Transformers and crossovers, you're losing me there.

teckniqs wrote: Yes of course, most VHF and UHF ham radio uses narrow FM. As for antennas there's lots of 70mhz (4 meter band) antennas which will work on the FM broadcast band with slightly different measurements. I'd definitely have a look around....

Ok thanks, I'll have a butchers about a bit.

The digital radios eg. Mototrbo, Tera/C2000 require a better signal than analogue radios.
The type of modulation they use isn't very robust against signal fade.

There's a good video on YouTube of analogue vs digital, where the operator takes a walk down the road and switches between tx modes and different power levels.

Where there was no digital reception, the analogue still worked.


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Pidworth wrote:Ah ok, perhaps I was being unrealistic then. I'm at the first of the options you said, though would like to at least get to the second. I think having a kit and following the steps would be kinda pointless if I don't at least have some idea why I'm doing things.

Kits are great for learning, but you're probably best off getting some non-RF kits first. Or, searching for something that you might like to make and find a schematic online, build it and then try to figure out why it doesn't work, or what happens if you don't fit a particular component, etc. Blow up some transistor in the process and you'll learn a fair amount that you won't learn from textbooks. However, the stuff in the textbooks is just as important.

As for the textbooks, I'm trying to think of one to recommend but haven't got anything in mind at the moment. The Art Of Electronics by Paul Horowitz and Winfield Hill is a very good book but is about £70 and about 15 years out of date if you get the second edition. This will only really bite you in the arse if you try to build some of the circuits in there as you will find that a good amount of the semiconductors are now obsolete.

Pidworth wrote:Sounds like I was thinking of going about things the wrong way then. Frequency domain and orders of magnitude I get. Is an oscillator in this setting doing a similar job as when used in a synth? I get how an amplifier works... Transformers and crossovers, you're losing me there.

When I say "understand how it works", I am referring to the following, for example:



Each component in the above schematic of a pretty basic class A amplifier has a specific role which contributes to the overall operation of the amplifier. This, as opposed to signal goes in, bigger signal comes out.
On a more broad level, an understanding of what the block-diagram level elements are doing in an amplifier is probably enough for now.

This is one of the basics which will lead to RF amplifiers - they aren't that far removed from audio amplifiers.

I'm not deliberately emphasising audio amplifiers or those in general, their design and understanding thereof, it was just convenient for illustration.

The challenge in electronics is to design and build an oscillator that is stable in terms of frequency, amplitude and phase. This is already served up for you on a plate in a synthesiser. You ask for a particular frequency (plus a set of optional harmonics) at a particular amplitude and you get it, whether it is synthesised from the synthesiser clock or generated from physical resonant elements. Or both.

What might help you is buying some cheap second hand kit from eBay so that you don't just rely on LEDs not working to indicate whether you've blown something up or not.
A multimeter is essential if you haven't got one already - these can be had for about £30 new on eBay. UNI-T make some fairly decent ones for the price - just don't measure high voltages with them as the internals aren't up to par.
You can get adequate oscilloscopes for under 20 quid if you're lucky and having an old analogue one will teach you about that bit of kit, compared to just pressing "autoset" on one of the newer ones.
Get yourself a signal generator (or use Audacity for free) and a variable power supply and start building some audio circuits such as a headphone amplifier, or a power supply, or something, just something basic so you can hopefully get an understanding of what is happening. Build an oscillator and see if you can get it stable. Try to avoid dicking around with the mains to start with, too.

I think thats some excellent advice from mr pranker and his example illustrates types of amplifier class, gain, collector current, filters, decoupling and bias!
Ive always loved audio amplifiers and i think its a perfect way to learn about alternating currents!
There are millions of circuits you could build and test for less than a tenner!
if youre feeling brave? you could easily build a quality audio amp up to 50watt? i wouldnt recommend any higher than 50watt, things get complicated at higher powers!
But again you will need significant knowledge on power supply safety, design and applications to get going!

The book mentioned by Mr Wise The Art of Electronics is available for free in pdf format.

http://iate.oac.uncor.edu/~manuel/libro ... 20Hill.pdf

Nice one for that shorty ...a free 1000+ pages to read through very nice ...

Didn't know about that free pirated PDF version. Cheers for that. I think I'll stick to the book though as I don't really get on with PDF versions. They send me to sleep!

What the heck! Just realised I posted in the wrong thread lol


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