guide/tutorial about radio links and codec methods?

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#1
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Hi, i am looking for a introduction about RF low power communications, talking about modulations, RF basics, and why manchester encoding is used for radio links.

I need to understand better this part for the datalink i am implementing for my AVR.

Unfortunately this recommended book http://www.rfsolutions.co.uk/aca... is not available in my country and I cannot buy online because I dont reach the minimum required for an order.

Could you suggest me a guide/tutorial online about radio links and codec methods?

Thank you very much!

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This is a very broad question! Modulation CAN include AM, FM, SIngle side band, PSK, AFSK, FSK, GMSK, and many, many, more.

Manchester coding is used for a very basic reason. If you pass most digital signals through an AC-coupled (high-pass) channel, the voltage level will vary with the data, and that makes it difficult to decode, reliably. So, people use Manchester, or NRZI or a variety of other encoding schemes that provide a nearly constant average voltage value.

That book really promotes those specific products. From you link, I cannot tell which module you are interested in. You might try Sparkfun for a broad range of RF modules available in single quantities.

http://www.sparkfun.com/commerce...

If you can describe what you are trying to do, more help might be available.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Type of data, data rate, range?

Leon

Leon Heller G1HSM

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Hi,

i am searching for a pdf book as introduction to radio design, what is PSK, FSK, PCB considerations, etc... explained as clear as possible.

Thank you ka7ehk, now I understand why Manchester is so popular, you answer is very clear but I couldn't get it by google.

About the project I am working on, it is a small network of devices (5 or 6) connected through radiolink to a central station with low baudrate (14Kbps is enough). It is just an idea for the moment, I haven't done anything yet. I am searching for the best method to establish the radiolink. It must be simple and cheap, solutions like Zigbee seems to be too expensive. I don't know yetm let's try with ISM band ;-)

Thank you very much, any idea or suggestion is welcome.

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I do not know about ANY good e-books on the subject. While perhaps a little expensive for you, my suggestion is much less expensive than most books. Take a look at www.arrl.org. This is the american ham radio organization. They have some very good paper books for not so much money. I very much recommend the ones by Hayward, often with other authors. He mostly writes about circuits rather than communications theory. I have NO idea what to suggest about that.

I can tell you that most, if not all, if the simple, low-cost short range modules made for 430MHz, or there-abouts, are simple on-off keyed, sometimes called OOK. This is really a very basic amplitude modulation. FM, PSK, and all those other good things are simply too costly for something that sells for a few euros or pounds or dollars.

Texas Instruments has a very nice chip that does several kinds of modulation, but is probably hard to get in small quantities AND you have to do a full board layout.

If you would like to chat a bit about this, feel free to PM me on this web site.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net