NewB: antenna and ADC howto
 

Hi all,

I'm Alexander and I'm a total newbe of radiofrequency comunication.
Fortunately I have a little knowledge of physics.

Now, my problem is: I want to record a raw UHF signal.
First step: I need an antenna. Any suggestion (web HowTos, pdf or anything
alike)?
Once I have the antenna and the circuitry behind it, I'd need a means of
recordingWhen I was at the university we had some nice toys which were able
to create (wired) digital signals. No I suppose there also are spectrum
analizers which could transform an analogic signal from the antenna to a
digital one so it can be easily recorded on a pc. Unfortunately I don't even
know how they are called! :-/ I called them ADC (as opposed to DAC), but
never heard this term actually. Could you give me a track to follow?

Thanks to anyone so kind to help,

Alexander

NewB: antenna and ADC howto
 

The antenna you pick should depend on just what you are trying to
receive. Could you give us any more info?

As for digitizing the signal, yes, you can actually buy receivers with
digital output, though good ones tend to be expensive. If you want
very broadband digitization, you can get ADCs that sample at 10^9
samples/second and above, but only to about 8 bits of resolution, and
accuracy even less than that. If you want to digitize only a
relatively narrow band, you can use analog techniques to convert the
signal to a lower frequency, or you can use an ADC that is capable of
"undersampling" -- accurately sampling a signal at a frequency above
half its sampling frequency. In either case, you need filters to
insure that the band of frequencies you let through doesn't cause
"aliasing". (You should be able to find plenty on that with a web
search.) Anyway, there are some key questions: what signals do you
want to receive, and what bandwidth do you want to digitize? Do you
want to be able to adjust the center frequency of the band you
digitize, or will it be fixed? What dynamic range do you need? What
amount of noise in the receiver can you tolerate? Without answers to
these basic questions and some others, you probably won't get the
results you seek. On the back end, another question is, what will you
do with the data? Can you record it or process it real-time without
choking on it? And finally, are you looking to buy a system, or build
one, or some combination?

Cheers,
Tom

NewB: antenna and ADC howto
 

First of all thanks for your answer.

K7ITM wrote:
The antenna you pick should depend on just what you are trying to
receive. Could you give us any more info?

I have to be able to read an UHF signal produced by an ISO-18000/6 (not B
version) RFID reader/tag signal. I first thought to directly use the tag's
antenna itself but have no idea of how to connect it to a sampler. Plus it
uses backscatter asa means of communication and don't know how this
influences any signal at the end of the antenna.

As for digitizing the signal, yes, you can actually buy receivers with
digital output, though good ones tend to be expensive.

Well, we are a research lab. Sooner or later I think we'll get our hands on
something if it's actually usefull and we ask for it. Nevertheless it has
to be as cheap as suitable.
--Inline Edit--: I have to ask our providers if they have any passive reader
they won't miss ;-) .


If you want
very broadband digitization, you can get ADCs that sample at 10^9
samples/second and above, but only to about 8 bits of resolution, and
accuracy even less than that. If you want to digitize only a
relatively narrow band, you can use analog techniques to convert the
signal to a lower frequency, or you can use an ADC that is capable of
"undersampling" -- accurately sampling a signal at a frequency above
half its sampling frequency. In either case, you need filters to
insure that the band of frequencies you let through doesn't cause
"aliasing".
(You should be able to find plenty on that with a web search.)
Thanks, I'll go and search as I don't remember very well. The band is as
narrow as 70MHz if I'm not mistaking. Take a look at

http://zone.ni.com/devzone/conceptd....25714D0067926D

As I told you I'm a total noob and I don't even know if there's only a
channel or more (though I think there's only 1)


Anyway, there are some key questions: what signals do you
want to receive, and what bandwidth do you want to digitize?

Well, there are lots of RFID protocols out there, but as this is our first
test I think we should do simple things. That's why I chose this protocol
(it should be simple (yet very complicated for me!) compared to the ISO
18000/6B).Do you think this should be easier in HF (125/130kHz) or VHF
(13.56MHz) domain (we have any kind of readers:-).

Do you
want to be able to adjust the center frequency of the band you
digitize, or will it be fixed? What dynamic range do you need? What
amount of noise in the receiver can you tolerate?

I'm not really a guru of telecom. The only thing I can say is that the S/N
ratio is *probably* no problem to me ... just get the reciever closer to
the emitter and I *think* it would be ok. Correct me if I say any nonsense.

Without answers to
these basic questions and some others, you probably won't get the
results you seek. On the back end, another question is, what will you
do with the data? Can you record it or process it real-time without
choking on it?

No real-time processing. At least for now and a good deal of time from now.
I first have to understand how this works. Plus once it's sampled I can do
all the tests I need to.

And finally, are you looking to buy a system, or build
one, or some combination?

It depends on how much time would cost (or how much money...).

Cheers and thanks again,
Alexander