cryptoguru

I want to send a mixed signal (possibly containing frequencies ranging 50-500MHz) on a 2.4GHz carrier or higher.

Does anyone know of any chips that can do this. I'm a bit of a newbie to the RF lingo and can't figure out from datasheets what's possible, what kind of terminology should I look for?

Most of the parts I've looked at seem to take a digital input, but I can't tell if they work with analogue (I'm from the UK that's how we spell it over here)

Would this part work?
http://focus.ti.com/lit/ds/symlink/trf2432.pdf

I want to be able to receive and demux at the other end, so a transceiver chip that would work for both ends would be nice.

Cheers

crypto

RadioRon

This part gives you the modulator and demodulator portion of a transceiver, and with its analog IQ interface you can adapt it to the analog modulation of your choice, as long as you can convert your baseband into I and Q components. The designers of this part assume that you are feeding it with a DSP. There is a major limitation in the baseband bandwidth that it is designed to handle. The data sheet says it is aimed at 802.16 applications so I recommend that you determine the physical layer bandwidth of an 802.16 signal by checking references. You can also see in the data sheet that the receiver side low pass filters are designed to have a bandwidth of 10MHz each. This certainely won't pass your 500 MHz of information.

Unfortunately, I don't know of any specific chip part numbers that provide a complete analog transceiver for 2.4 GHz. Pretty much all the ones I'm familiar with have data in/out only and these will not work with an external analog baseband signal.

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RadioRon

crusty

might want to aim for a lower frequency if it's not that important that you specifically need to broadcast on 2.4. Usually lower frequencies can travel a bit farther with less power than the higher freqs. Also there's a lot more analogue modulators available for lower freqs. I've heard of people using their own firmware for some wireless 2.4 cards to get them to tx other things than digital, though i've HEARD about it, i don't know if it is possible.

cryptoguru

Cheers guys ... that's helpful.

RadioRon: you said that my bandwidth is too wide for that IC ... would that still be the case if I mix a 50MHz and 500MHz sine wave together as the signal? Obviously the bandwidth of each part is small, but is it their encoded bandwidth that counts?

Crusty: it doesn't need to be as high as 2.4GHz I just picked that because there seemed to be a lot of standard RF parts using that carrier (for obvious reasons). Are there any solutions you know of for a carrier around 1GHz?

Would it be easier for me to just make something using components?
A simple AM transmitter - receiver with a 1GHz carrier encoding two sine waves, one at 50MHz and one ate 500MHz.

Thanks again.

JimB

Yes!

Please realise that this is absolutely ridiculous, and will not work.

Unless you are using a closed system, ie a coax cable between transmitter and reciever, your signal will be splattering all over other uses of the radio spactrum between 500 and 1500Mhz.

Why is it that some of the people on here with no radio knowledge or experience come up with these fancyfull schemes which for the other users of the radio spectrum can be at the best annoying, and a worst downright dangerous.

JimB

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RadioRon

Jim has a good point. One of the facts of life we RF people learn very early is that government regulations dominate every choice we make when designing new or unique RF devices. Without knowing more about Crypto's application, the type of modulation used, transmitter duty cycles, his intentions to build one or many, what country he his in, if he intends to sell any or sell the design and so on, it is hard to recommend what best frequency range to use.

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RadioRon

cryptoguru

It's all an issue of power really isn't it? ... I just want to modulate 2 weak sine waves over a carrier. How will that interfere with anything?

Plus the side-bands won't move they'll just be a tiny narrow spike that no-one outside my house will see. The carrier (if its 2.4 GHz) wouldn't be an issue as it would be like a standard wifi carrier.

I can't really explain the idea ... except to say I want to send 2 sine waves , roughly 50MHz and 500MHz on a high frequency carrier. The shorter the carrier wavelength, the better. It's for wireless use within a room.

Want to build one to test out a theory!

I'm a mathematician, not an RF engineer, but I'm a fast learner ;-)

RadioRon

Well, yes it is simply an issue of power. But it is impossible to answer your question unless I know how much power.

The sidebands will fall outside any of the popular ISM bands (like those used by WiFi or cordless phones). The band at 2.4 GHz often used for WiFi ranges from 2400 to 2483.5 MHz. As a mathematician, I'm sure you will recognize that multiplying the carrier sinusoid by your 50 MHz and 500 MHz sinusoids will result in sum and difference frequencies, so if your carrier is, say, 2450 MHz, your sidebands will be at 1950, 2400, 2500 and 2950 MHz so the only one within the ISM band is the one at 2400.

But this is all nitpicking. The fact is that if you are putting out a total power of, say, 0 dBm, with a carrier at 2.45 GHz, then the chances that you will be interfering with something important is awfully low because your signal is only going to go a couple of hundred feet at best anyway, so for the sake of experimentation, don't worry about all these legal issues and just go for it.

So on your original questions, I think you will be best off by using basic RF building block chips instead of an integrated trasnceiver IC, and get the help of someone who has built RF circuits at 2.4 GHz, because they won't work if you don't. As for which building blocks, the easiest might be :

1 national LMX series synthesizer IC
1 VCO module that runs around 2.4 GHz
1 vector modulator IC for use at 2.4 GHz

Your 50 MHz and 500 MHz sine waves will be able to drive the vector modulator directly if the modulator has analog IQ inputs.

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RadioRon

kchriste

Why not just sent the two sine waves (50Mhz and 500Mhz) directly since they are already RF and you don't care if you are on a legal frequency anyway?

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cryptoguru

But I reckon I can test my theory to within a decent accuracy using just one sine wave at 40.68MHz (which is the center frequency of a license-free band).
This should be much easier to build!
Anyone know of any standard transceiver ICs that would do this well?

Also does anyone know what the best accuracy a phase comparator could run at on this frequency? And/Or any parts?
The best I could find was around 1 degree accuracy, is that typical or could I do better than that?

crypto

ramukumar

Hi
I am newbie, I like to do project for which i need circuit for transmitting video and audio signals for about 10M and also the circuit to receive it