• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

RF detector

Status
Not open for further replies.

narco

New Member
I am interested in building a simple RF detector. One that vibrates upon the presence of RF signals would be great. I would like to use this item as part of a counter surveillance kit that i am putting together. Has anyone built one, or does anyone know where I might be able to find plans to build one? Thanks for reading.
 

Klaus

New Member
Its not quite as simple as you might think :wink: . RF covers a rather wide spectrum nowadays and any detector would have to be frequency specific to detect weak signals. If your detector is too broad banded you would soon get annoyed by all the false readings from the RF noise everywhere around (if you live in a city).
Your detector would need a tuned aerial and an amplifier. A vibrating output is rather novel, most people would settle for a meter or some indicator lights to show signal strength.
If the RF is very powerful, like underneath a radio station transmitter tower, then a neon or fluorescent lamp might light up all by itself :D but that isn't what you had in mind, is it?
 

trikebuilder

New Member
fm bug detector

check out the circuit at:

hptt://www.zen22142.zen.co.uk/Circuits/rf/bugdetector.htm

You could add a transistor driver to the circuit, and use a small pulsar vibrator from a cell phone for the vibration you want.
 

narco

New Member
The link works if you correct the typo. In the begining of the link it is stated as being hptt. All you need to do is change it to http-and the rest of the address.
 

laihuhng

New Member
What about frequency higher than this? As you all know, recently there is a lot of Wireless Pinhole camera anywhere. Anyone has any circuit that would able to detect both 1.2GHz and 2.4GHz? The detector is too expensive to buy. DIY would be better and nice. Please help..... :roll:
 

zachtheterrible

Active Member
1.2, 1.4 GHZ is gonna be a real pain if you dont know what you're doing. high frequencies like that are affected by EVERYTHING. For ex. if the tracks on ur PCB r 2 big or small, it'll affect frequency and/or stability.
 

laihuhng

New Member
That's the case, means no circuit available, right? And, this 150MHz detector would not be able to capture these 2 frequencies too, is it?
 

zachtheterrible

Active Member
Of course there's circuits available, probably some that you can build. I was just saying that its gonna b very difficult if you totally dont know wut ur doing. if ur experienced in electronics (which you dont sound like u r), u can probly do it. im sure that theres detectors in these two frequencies that you can buy, which is your best bet. theres no way that the 150 MHZ would be able to pick up these two frequencies.

You can try building this circuit here, if you connect it 2 a voltmeter, it will show voltage, the diode has to be germanium type (at least thats wut it said on the website) u might be able to use something else (but dont quote me on that) i didnt put the cap on cuz @ the time i didnt have one but the circuit still works. i think its there to filter out power lines frequencies (60 hz here in america). gnd doesnt have to be connected to anything, its there for better sensitivity if youre testing out an RF circuit. put ur voltmeter on a low voltage setting, like mv.

I think that this circuit should work w/ high frequencies. dont build it until someone verifies this cuz im not sure. the thing that im not sure about is if the diode has to be high frequency. i could look this up but am 2 lazy. if this circuit will work, you could probly make an amplifier for it or something, ill let someone else tell you about that. hope this helps :D
 

Attachments

plot

New Member
You gotta have high frequency diodes. Best way to find out if it's high frequency... crank up the frequency generator and try it out. A simple DC Diode check to see if the diode works won't do it...
 

xda_xdi

New Member
RF detector for metal type of minerals

I'm an engineering student, the new learner of electronics stuff. My final project is "mineral discrimination using electromagnetic waves (EM-waves)".
Due to time constraint, my project will be focus on detection of metal type minerals only. Through out my research, I found that the EM-waves spectrum will be affected by variation of the material conductivity. So, I would like to use the conductivity property of each metal type mineral and look up their variation in EM-waves spectrum.

I found the formula that relates the conductivity of the material with frequency. My idea is to use the RF detector to receive the induced frequency from the metal type of minerals. I am not to sure whether EM-waves can be categorized as RF signal. Are these two signals are adequate? :confused: I would like to use the circuit in the link given by trikebuilder; but I want to modify the detection frequency. What step should i take in order to change the detection frequency of my circuit? what factor or component that contribute to the respective detection frequency?If let say I want the circuit to receive 5 different value of frequency, is this circuit capable of doing it? if not, can anyone suggest how to do it? really need your help! thanks :)
 

audioguru

Well-Known Member
Most Helpful Member
An RF probe was used a hundred years ago when there were hardly any transmitters.
Today it will pickup every radio station, TV station and taxi-cab radio in town.
Millions of other radio transmitters are also used and will also be picked up.
UNLESS YOU ARE ON MARS or in a 3rd world country.
 

xda_xdi

New Member
audioguru, thanks for the reply.
But can anyone else help me with my project that i describe before?:(
Some guidance on RF detector should be nice..
Thanks
 

transistance

New Member
audioguru, thanks for the reply.
But can anyone else help me with my project that i describe before?:(
Some guidance on RF detector should be nice..
Thanks
To select different bandwidths you can use Switched Capacitor Filters. They can be very precise going up to 8th order.

Also, searching this forum for "frequency detection" or "graphic equalizer" will give you a large source of information.
 
Last edited:

audioguru

Well-Known Member
Most Helpful Member
An audio switched capacitor lowpass filter is useless at VHF frequencies.
An audio graphic equalizer uses low frequency opamps.
 

transistance

New Member
I didn't know mineral discrimination was a VHF application sorry for the misguidance. It wasn't mentioned in the post.
 

1oskar

New Member
Like say audioguru
An RF probe was used a hundred years ago when there were hardly any transmitters.
Today it will pickup every radio station, TV station and taxi-cab radio in town.
Millions of other radio transmitters are also used and will also be picked up.
UNLESS YOU ARE ON MARS or in a 3rd world country.
I can add any local oscillator in receivers , synchrony oscillators from TV set and CRT monitors.(It is hard to write all interference source today)

It is correct in any city. Simple RF probe cannot help(only make wrong image).
PC have also RF and will be cause a wrong measurement(I was use industrial receiver and wonder "how many signals are in specific amateur radio frequency?" But all this signals was from local area network in building 141MHz 144MHz etc.From common PC)

But it is not impossible mission.:D

Look like joke how simple device can easy work for this task.(Proven by government agency long ago)
Because most bugs are triggered through certain frequencies, it is very simple “to build a small sweeping device that will trigger any bug present".
Or even only passive RF receiver.Bug will be triggers with own signal.:D
Add just , remove coil from original draw. Instead make a resonator on 150 MHz so call Lecher resonator http://lea.hamradio.si/~s53mv/counter/lecher.jpg
But for this project must be shorter than 1/4 wave length(300/150=2 meter/1/4=50 cm so must be shorter much more) and to tune up, use variable capacitor.This cannot give you narrow band but it will be cut off much more interference. Also leave meter to see signal strength but not importance. Importance is add audio amplifier to run speaker.
Why, bugs are to simple transmitters low power, so if you build simple RF wide frequency receiver , passive receiver. And importance
do not use headphone etc for signal presence no. Use speaker only, and what happened? Bug pick up audio and transmit , when a simple device receive RF signal you can hear on speaker and when you near bug(few feet)
bug will be pickup signal from speaker then amplified and transmit, bug detector receive RF from bug this will be appear like sound oscillations.(Like whistle sound) And you do not need to know exact frequency of bug and forget other source of RF, they cannot create negative feedback to make sound oscillations.
Phone bug use electricity from phone line and work only when pick up phone(easy close the electric circuit and bug in serial with phone start transmit RF). So pick up phone receiver place near phone (live open line to bug transmit)
I believe this is electronic project easy to do.(Also standard anti surveillance procedure) Good enough? For simple device?
How to do it for hidden camera I do not know(can help only what I was try), and such this device are integrated mostly camera and low power transmitter on pretty high frequency. But still are rule no transmitter can be hidden. Even transmitters in burst mode radiate RF , and bugs device are pretty simple and radiate RF all time.(Audio or video same thing).
;)
 
Last edited:
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top