Resources for understanding RF front end design with TI CC1200 - Page 1
Forum section: electronics / beginners

author: Apothus
author_rank: Contributor
timestamp: October 05, 2014, 04:22:20 am
content: Previously whenever I have worked with any radio units they have been XBee type modules or completely integrated units that simply needed a 50ohm impedance trace. I have never played around with pi networks or the like.However I want to start working with the CC1200 transmitter module and possibly combining it with the cc1190 booster front end. Looking at the reference design and reading through the notes there is a clearly a lot more going on with the output of these modules. Is this because they can operate at different frequency bands?I have been looking to find some information on how I can understand how to build these front ends and what would be required to build a scehmatic that also incorporates the CC1190 front end amplifier. However I am not sure where to start. Can anyone link me to some good resources for understanding how to build these circuits or primer on RF design?Where should I start with this project? should i just buy the evaluation modules and understand them first?How can I begin to debug my design and understand the performance of the system? Can I do it just by running range tests at the local park or will I need to look at investing in some dedicated RF design equipment?CC1200 Data sheethttp://www.ti.com/general/docs/lit/getliterature.tsp?genericPartNumber=cc1200&fileType=pdfCC1200 Reference Designhttp://www.ti.com/lit/df/tidr180/tidr180.pdfCC1190 RF Front end Data sheethttp://www.ti.com/product/CC1190/technicaldocuments

author: tggzzz
author_rank: Super Contributor
timestamp: October 05, 2014, 08:21:58 am
content: Quote from: Apothus on October 05, 2014, 04:22:20 amI suspect that would be illegal there, for the same reason it would be illegal here: you might be stomping over other people's radio signals.You will probably need to demonstrate understanding of the local laws, RF component non-idealities, and then be able to demonstrate that your equipment won't interfere with other transmissions.

author: KJDS
author_rank: Super Contributor
timestamp: October 05, 2014, 08:44:18 am
content: I've had a very quick look. There's a balun on the LNA inputs and some simple filtering.I suspect that the only way to use these legally is to run them on an amateur band assuming that you have the appropriate licence.

author: Apothus
author_rank: Contributor
timestamp: October 05, 2014, 01:58:22 pm
content: Quote from: tggzzz on October 05, 2014, 08:21:58 amFrom my understanding of these modules they are configurable for different bands. My expectation was to run them in the 915-928MHz ISM band. Considering the max TX is 15dBm with the cc1200 on its own I would still need the cc1190 to max out to the full 30dBm (assuming i implement some for of channel hopping).Considering the class of device and the low transmit power I don't think there would be much harm testing such devices at a park regardless of the frequency.Quote from: KJDS on October 05, 2014, 08:44:18 amwhat is the purpose of a balun on the LNA and how can I find information on the filtering? what is the signal trying to filter out? is that recieved noise from the antenna or is that to filter output? How could i learn to calculate these values?What could I then do to test them?

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 05, 2014, 02:19:46 pm
content: Different frequency bands are legal in some parts of the planet (and some countries), but illegal in other areas. You could get yourself in serious trouble and even cause an emergency situation by attempting to transmit (especially at higher power) on frequencies reserved for other uses.Many of these commodity RF devices can be used in different frequency bands that may or may NOT be legal in YOUR area. BEWARE!

author: tggzzz
author_rank: Super Contributor
timestamp: October 05, 2014, 02:26:46 pm
content: Quote from: Apothus on October 05, 2014, 01:58:22 pmSo, you are planning on transmitting 32mW to 1W in an ISM band. I make no comment about the legality of that in your locality.However,all RF components are non-linear to some degree. That means theywill also be transmitting in other bands. The degree to which that is or is not a problem for other users will depend on the non-linearities, transmitted power & frequencies, location, etc.A quick self-test, i.e. I don't want to know the answer!...Given your frequencies and intended modulation, what will the power transmitted as a result of second and third harmonic distortion, and at what frequencies will they appear?What does the specification of IP3 compression point mean, and how is it related to radio performance?If you can't honestly answer those questions, I suggest you contact you local ham radio enthusiasts.In short: "I don't think there would be much harm testing such devices" is irrelevant - what matters is what you actually do and whether it causes harm.

author: Apothus
author_rank: Contributor
timestamp: October 05, 2014, 03:32:19 pm
content: Quote from: tggzzz on October 05, 2014, 02:26:46 pmI do not say that to be blasé however my expectation of the interference caused from a sub 1W transmitter in a field vs the interference and noise generated by a running microwave would be relatively minimal and little cause for alarm. Considering this is a somewhat new field for me I am here to learn.Quote from: tggzzz on October 05, 2014, 02:26:46 pmI will certainly try to track some down. I am in Western Australia, if anyone knows when/where they meet that would be a big help.As for understanding those questions. That is the information I am wanting to find, where are the resources I can look at to learn to ask those questions, what search terms do I put into the all mighty answer machine? Is there a good undergrad/grad level book to pick up this field? That is what I am asking for in this post.In regards to legality.According tohttp://www.comlaw.gov.au/Details/F2013C00396] this  the frequency band and transmit power of 1W are legal in OZ for frequency hopping Radio Local Area netowkrs with hopping or 3mW for static.Again I am learning and paying attention to the laws vs just using another 900Mz XBEE pro or random Chinese RF transmitter.

author: tggzzz
author_rank: Super Contributor
timestamp: October 05, 2014, 04:30:19 pm
content: Quote from: Apothus on October 05, 2014, 03:32:19 pmNot a valid comparison, since microwave ovens operate at different frequencies (and therefore won't splat on the same third parties), and have somewhat controlled modulaton characteristics.Consider that GSM phones work when receiving signals that are at -100dBm, i.e. 0.0000000000001 of the 1W you might transmit at (i.e. 130dB down!). (And we won't even consider the power that isn't being received from the Voyager probes)QuoteIf only it was that simple.RF engineering takes alongtime to learn and isverydifferent to analogue, let alone digital.And even when you've got it all under your belt, the practical nasties come and bite you: there are many things that you just have to measure, since there are too many effects to be able to predict, although very expensive CAD packages can help, if and only if used appropriately.And then you have to be aware of the "rusty bolt effect". One consequence is that you don't know exactly which combination of comms frequencies are usable on a naval ship - to a large extent you have to "suck it and see". Repeatedly, since they can change during the ship's lifetime. And even then, sometimes you can be right royally screwed, as happened to HMS Sheffield in the Falklands conflict.Local radio hams are your best bet for a practical experience, and they may even have the test equipment necessary to measure the spurious emissions.QuoteAssuuming the manufaturere isn't lying through their teeth, theire equipment should have been "type certified" before use.

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 05, 2014, 05:11:44 pm
content: Microwave ovens virtually all operate at one of the ISM frequencies, which are reserved for non-telecommunication applications. For example, consumer microwave ovens almost universally operate on 2.45 GHzNow 2.45 GHz is also the band that Bluetooth uses. But of course Bluetooth is defined as a SHORT range communication system, and interference from microwave ovens is minimal unless you are very close to the oven. Clearly, microwave ovens are not communication-related, but other things like wireless telephone systems are also being designed for 2.45 GHz, and people are experiencing interference there. Which is why we are seeing movement of short-range wireless devices up to the next-higher ISM band, 5.8 GHz.

author: Apothus
author_rank: Contributor
timestamp: October 06, 2014, 01:45:55 am
content: Quote from: tggzzz on October 05, 2014, 04:30:19 pmI think I must be a masochist at heart. To me RF electronics has always been described as a bit of a dark art that is misunderstood by most and half understood by others. So I think that is why I have become so interested in itIt also looks like more and more devices are moving towards using wireless systems for communication. Especially technologies like ZigBee etc. So it would be interesting to be involved with them.I have got in contact with one of my local [url =http://www.harg.org.au]HAM groups so hopefully I hear back from them and join their meeting on the weekend.Quote from: tggzzz on October 05, 2014, 04:30:19 pmThat is surprisingly sensitive! Are towers able to detect any of that interference and skip those frequencies/channels or is it just bad luck for whoever's phone is assigned those frequencies?Where did you start learning about RF design? there must be some text book I can pick up before i meet with anyone on the weekend, at least i wont sound like a complete fool

author: tggzzz
author_rank: Super Contributor
timestamp: October 06, 2014, 09:12:48 am
content: Quote from: Apothus on October 06, 2014, 01:45:55 amYup, on several counts! Go for it, have fun, but be prepared for a steep learning curve."Ignorance can be cured, stupidity can't"QuoteThe base stations can work at those power levels since they have extremely good and bulky RF filters and low-noise front ends, and have higher power transmit amplifiers. The handsets don't, and so have poorer performance. When reception is too bad (due to either signal strength or distortion), either end can "hand off" to a different frequency or different base station. There is an option in GSM for slow frequency hopping, which might mitigate some poor reception, but I don't know whether any carriers implement it.QuoteWhat make you think I know anything, other than "here there be dragons"?The hams will have good information available, and when someone that is willing to learn walks in the door, I would expect them to be very welcoming.

author: Apothus
author_rank: Contributor
timestamp: October 06, 2014, 12:27:25 pm
content: Quote from: tggzzz on October 06, 2014, 09:12:48 amI hope so, going to a meeting on the weekend!Thanks for the warning