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Help with electronics proyect: RF radar.

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kiewirevo

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Hi there.

I'm new to this forum and id like a little help with my electronics proyect.

ive seen a thread about an frecuency detector but that thread is long time inactive, so id like some help making a new thread.

my proyects is basicaly a device that detects certain kinds of frequencies and shows it in a map like a submarine radar... the thngs i read about where envelope detectors, LM567 and band pass filters. now i have good electronics knowledge but the things i didnt understand about them is how to make the reciever?... my idea was to make a kind of antenna that emits in a straight line, mounting it on a motor to make it spin so it can detect several kinds of devices.

the devices i want to detect are: celular phones (depending on what bands they are), wireless mouses, routers, etc. but my problem is that i dont know how to make the reciever circuit recieve (excuse the redundance).

i want to start out simple making a filter or circuit that recieves a certain frecuency and turns on a LED depending on how close it is, so when its closer itl be bright and when it gets further away ill dim slowly. Then slowly making several circuits to several frecuencys so it can detects the devices. Now the problem persists in how to make the antenna or the reciever circuit.

To complete the idea i want those circuits connected to an arduino so it can identify the diferent voltage inputs to graphic it in an map using a program gnuplot or matplotlib.

so that is basically the idea of my proyect any help or advice would be greatly appreciated :)... thanks in advance.
 
kiewirevo, you may want to rethink your project.. RF triangulation is probably one of the most complex subjects from both a digital and analog perspective that you can tinker around with. It generally takes equipment costing multiple tens of thousands of dollars to do what you're wanting to do, unless you can more specifically narrow the frequencies you're interested in, the distances you're interested in, and specify the accuracy with real numbers there's no way to respond properly to your post.
 
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sorry

kiewirevo, you may want to rethink your project.. RF triangulation is probably one of the most complex subjects from both a digital and analog perspective that you can tinker around with. It generally takes equipment costing multiple tens of thousands of dollars to do what you're wanting to do, unless you can more specifically narrow the frequencies you're interested in, the distances you're interested in, and specify the accuracy with real numbers there's no way to respond properly to your post.

im sorry i dont intend to make a big antenna or something i just want a small antenna that recieve in a perimeter of 5-10 meters or at least take small radio frecuencys to start out... lets say i want my radar to recieve from 80KHz and 100KHz what elements do i need to make it?
 
It might be easier to start with your original suggestion, which is to receive signals from wireless routers and such kinds of devices. The reason for this is that it is easier to make an antenna with narrow directivity at higher frequencies. However, this is still a very challenging project.

One way to build the receiver is to use an evaluation board for a Logarithmic Detector IC. These ICs are made by companies like Analog Devices and Linear Technology. An evaluation board is better than starting with the bare IC because it is too difficult for the beginner to get the IC to work on his own. Many log detectors are broadband, so for receiving signals from specific devices you would have to put a band pass filter between the antenna and the log detector, a filter that is chosen for the devices you want to receive. For example, most WiFi devices operate in the 2.4 GHz band, so a band pass filter at 2.4 GHz would be appropriate for these. Cell phones operate in several bands including 1750 to 2000 Mhz, 825 to 960 Mhz for examples. Filters are available for all these bands.

It is possible to buy band pass filters in the form of a small circuit board with a surface mount filter soldered on the board and two RF connectors.

In order to build an antenna with a narrow beamwidth, such as you imagine, you will probably have to make something special. To start with, there are many antenna designs described on the web for 2.4 GHz Can antennas and this would be a good starting point.
 
It might be easier to start with your original suggestion, which is to receive signals from wireless routers and such kinds of devices. The reason for this is that it is easier to make an antenna with narrow directivity at higher frequencies. However, this is still a very challenging project.

One way to build the receiver is to use an evaluation board for a Logarithmic Detector IC. These ICs are made by companies like Analog Devices and Linear Technology. An evaluation board is better than starting with the bare IC because it is too difficult for the beginner to get the IC to work on his own. Many log detectors are broadband, so for receiving signals from specific devices you would have to put a band pass filter between the antenna and the log detector, a filter that is chosen for the devices you want to receive. For example, most WiFi devices operate in the 2.4 GHz band, so a band pass filter at 2.4 GHz would be appropriate for these. Cell phones operate in several bands including 1750 to 2000 Mhz, 825 to 960 Mhz for examples. Filters are available for all these bands.

It is possible to buy band pass filters in the form of a small circuit board with a surface mount filter soldered on the board and two RF connectors.

In order to build an antenna with a narrow beamwidth, such as you imagine, you will probably have to make something special. To start with, there are many antenna designs described on the web for 2.4 GHz Can antennas and this would be a good starting point.

thank you for the suggestion now i know i can make band pass filters with OPAM LM324 but isnt there a more... dedicated OPAM for this because id like a clean reception and not too many parasite signals (if you know what i mean). i found a page that calculates band pass filters but im not sure what gain i want or what capacitator to use https://www.changpuak.ch/electronics/Butterworth_Bandpass_active.php . i already asked my teacher to help me with the construction of the antenna and hes going to lend me a book about it.

also the Logarithmic Detector IC: MAX2016 and the AD8318 looks like what i need to make the filters... so i guess i need to look for the "general aplication circuit"?.. any pointers..? and thanks :)
 
You are not making a radar. It uses reflected radio energy. You are trying to make a radio transmitter direction finder.

The lousy old LM324 quad opamp has trouble with frequencies above only 2kHz (2000 Hz). Most other opamps work well up to 100kHz.
Maybe if you amplitude-modulate the carrier with a low audio frequency then an LM324 opamp can detect the strength of the detected audio signal.
But your carrier frequency is so low that a directional antenna must be huge!
 
You are not making a radar. It uses reflected radio energy. You are trying to make a radio transmitter direction finder.

The lousy old LM324 quad opamp has trouble with frequencies above only 2kHz (2000 Hz). Most other opamps work well up to 100kHz.
Maybe if you amplitude-modulate the carrier with a low audio frequency then an LM324 opamp can detect the strength of the detected audio signal.
But your carrier frequency is so low that a directional antenna must be huge!

i just called it a RF radar becuase it sounded nice... it was just meant for a name. but the IC's ive put in my last post are the most probable ones im going to have to use. and also remember im not making a radiostation i just want an antenna that can detect things in a room. not a neighborhood.. also the idea is to make a uni-directional antenna (emitting in 1 direction) so make things more easier so i can make it spin arround mounting it on a stepper motor, the idea of making an 1 direction antenna is to make things easier if not ill make a normal one... depending on what costs less or whats easier to make... also its a project that came in my mind and im collecting the information i need to make it, if i cant make it i cant. im just investigating the necessary to make it possible, also if there is a small chance i can make it then ill just do it. its something i want to make to be proud of myself XD (no offense).
 
Have you seen a TV antenna up close? It is directional. It is pretty big. Its lowest frequency is (was) 55MHz in North America.

Detect things? Do you want to transmit (emit) a radio signal then receive its reflection from something nearby? But many things do not reflect a radio signal. The receiver must be turned off during transmit then it must turn on extremely quickly because radio travels at the speed of light. The time taken by the reflection is the distance. But the time is very close to zero.

There are many other problems you have not thought about (a screen showing location and distance of objects?).
 
Have you seen a TV antenna up close? It is directional. It is pretty big. Its lowest frequency is (was) 55MHz in North America.

Detect things? Do you want to transmit (emit) a radio signal then receive its reflection from something nearby? But many things do not reflect a radio signal. The receiver must be turned off during transmit then it must turn on extremely quickly because radio travels at the speed of light. The time taken by the reflection is the distance. But the time is very close to zero.

There are many other problems you have not thought about (a screen showing location and distance of objects?).

eem ok. where i study there are devices that detect frecuencies, the professor told me i could use the reciever antenna of it for my proyect so in case i cant make the antenna i can use that. also i just want to "recieve" signals i dont want to emit nor bend or anything like it. i just want to "recieve" the signal and i know its possible so the only thing im asking is "pointers on how to make it" not being lectured on what i can or cannot do or what i didnt thought about. just pointers on how i can make an reciever circuit or bandpass filters.

in the case i cant make it id like to know how i can make a good bandpass filter and what components are recomended to make it and what do i need to make a antenna and what kind of things do i have to use. is there a page or a book you guys recomend, etc.

please just point me into a direction and i will follow and investigate the following. at least today the professor and i investigated about the IC ADL5592 which is a 250 MHz to 2400 MHz RF Variable Gain Amplifier which i can make a atenuator/filter to recieve the designated frecuencies i want... so i dont think im that far of or not?
 
i just want to "recieve" signals.... just pointers on how i can make an reciever circuit or bandpass filters.

....id like to know how i can make a good bandpass filter and what components are recomended to make it and what do i need to make a antenna and what kind of things do i have to use.
Maybe you want to make a spectrum analyser? Look at it in Google.
A spectrum analyser shows on a display many radio frequencies that it receives. It can use a directional antenna or an antenna that picks up signals all around. It is a very complicated circuit. It does not show direction nor distance. Like all radios it has many bandpass filters. It will show the radio frequency used by an old cell phone (new cell phones use many frequencies at the same time), a wireless mouse or a wireless router.
Here is a photo of the display of a spectrum analyser showing many radio frequencies with decreasing amplitudes and the same frequency spacing.
 

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Maybe you want to make a spectrum analyser? Look at it in Google.
A spectrum analyser shows on a display many radio frequencies that it receives. It can use a directional antenna or an antenna that picks up signals all around. It is a very complicated circuit. It does not show direction nor distance. Like all radios it has many bandpass filters. It will show the radio frequency used by an old cell phone (new cell phones use many frequencies at the same time), a wireless mouse or a wireless router.
Here is a photo of the display of a spectrum analyser showing many radio frequencies with decreasing amplitudes and the same frequency spacing.

You can measure distance using an SA if you know what the transmitted power is at what range and how much the signal deteriorates on it's way to the analyser. This would be impracticle for short distance measuerments becuase the the detector would have to be extremely sensitive to changes in frequency or amplitude. For a much longer range it can be done, but it won't be easy.

If memory serves, the eirlier forms of radar used a form of spectrum analysing to approximate a distance to the target but weren't able to get a target size. Speed and altitude were calculated by measuring the changes in signal levels as the target moved.
 
Maybe you want to make a spectrum analyser? Look at it in Google.
A spectrum analyser shows on a display many radio frequencies that it receives. It can use a directional antenna or an antenna that picks up signals all around. It is a very complicated circuit. It does not show direction nor distance. Like all radios it has many bandpass filters. It will show the radio frequency used by an old cell phone (new cell phones use many frequencies at the same time), a wireless mouse or a wireless router.
Here is a photo of the display of a spectrum analyser showing many radio frequencies with decreasing amplitudes and the same frequency spacing.

ok i can work with that thanks ill dig in to that :) thanks.
 
You can measure distance using an SA if you know what the transmitted power is at what range and how much the signal deteriorates on it's way to the analyser. This would be impracticle for short distance measuerments becuase the the detector would have to be extremely sensitive to changes in frequency or amplitude. For a much longer range it can be done, but it won't be easy.

If memory serves, the eirlier forms of radar used a form of spectrum analysing to approximate a distance to the target but weren't able to get a target size. Speed and altitude were calculated by measuring the changes in signal levels as the target moved.

hmm well i dont want distance nor height i just want to pick up the signal in 1 direction so i can map it in a graphic interface... i think that if i make a circuit that converts frecuency to dc current i can give it a "kind of proximity sense" to it... like when the circuit returns me 5V ill make the dot appear very close to the center of the map and when it returns 1v ill make it appear a little farther. get my point?.

also the measuring i want isnt changes its just a determinate set of frecuencies like 780MHZ to 820MHZ and so on... and i dont know what an "SA"(or at least not the abbreviation) . and also thanks im getting smarter by the post XD.
 
hmm well i dont want distance nor height i just want to pick up the signal in 1 direction so i can map it in a graphic interface... i think that if i make a circuit that converts frecuency to dc current i can give it a "kind of proximity sense" to it... like when the circuit returns me 5V ill make the dot appear very close to the center of the map and when it returns 1v ill make it appear a little farther. get my point?.

also the measuring i want isnt changes its just a determinate set of frecuencies like 780MHZ to 820MHZ and so on...
You are confusing "frequency" with "detected signal strength".
You are also confusing "transmitted power" with "detected signal strength".

i dont know what an "SA"
It is Spectrum Analyser. I showed its display and I said to look at it in Google.
 
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You are confusing "frequency" with "detected signal strength".
You are also confusing "transmitted power" with "detected signal strength".


It is Spectrum Analyser. I showed its display and I said to look at it in Google.

o sorry i didnt knew the abbreviation was SA for that and sorry for the confusion
 
i just want to pick up the signal in 1 direction so i can map it in a graphic interface... i think that if i make a circuit that converts frecuency to dc current i can give it a "kind of proximity sense" to it... like when the circuit returns me 5V ill make the dot appear very close to the center of the map and when it returns 1v ill make it appear a little farther. get my point?.

Yes we understand what you want to do, but you have to understand that it doesnt work that way.

A given signal strength and therefore output voltage level from the receiver detector cannot be directly related to the distance of the transmitter from you. Why you ask? ...

say you got a 2Volt output from the receiver ....it could be a weak signal very close or a strong signal a long way away... you would have absolutely no way on knowing which it was. So what you plotted on the screen would be meaningless.

the complexities of what you are trying to achieve would appear to be far in advanced of your apparent knowledge of even basic radio receivers and how they work.

cheers
Dave
VK2TDN
 
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Yes we understand what you want to do, but you have to understand that it doesnt work that way.

A given signal strength and therefore output voltage level from the receiver detector cannot be directly related to the distance of the transmitter from you. Why you ask? ...

say you got a 2Volt output from the receiver ....it could be a weak signal very close or a strong signal a long way away... you would have absolutely no way on knowing which it was. So what you plotted on the screen would be meaningless.

the complexities of what you are trying to achieve would appear to be far in advanced of your apparent knowledge of even basic radio receivers and how they work.

cheers
Dave
VK2TDN

well i will try to make it anyways and will go back to the forum with progress.
 
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