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    narrow beam antenna and low sensitivity receiver

    Hi,

    I'm planning to create a laser like(or narrow beamwidth) em radiation for a project. At the transmitter side I would have a parabolic antenna and at the receiver side I need an antenna with less sensitivity. More like, if the radiation falls on it only then it must give out a signal, like an LDR placed in the beam of a laser. How do i start?

    Thank you.

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    Re: narrow beam antenna and low sensitivity receiver

    What is your frequency? What is beamwidth (in degrees)? For tenth GHz range it would be difficult to make something laser-like. Even few degrees beam would be a problem. You can start with calculating power level in dBm that needed at receiver side to read signal without error. Then knowing distance you can add attenuation factors. Summing up will give you required transmit power.



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    Re: narrow beam antenna and low sensitivity receiver

    Quote Originally Posted by Terminator3 View Post
    What is your frequency? What is beamwidth (in degrees)? For tenth GHz range it would be difficult to make something laser-like. Even few degrees beam would be a problem. You can start with calculating power level in dBm that needed at receiver side to read signal without error. Then knowing distance you can add attenuation factors. Summing up will give you required transmit power.
    The frequency I thought was 2.4GHz, as they are pretty standard and easily available. For now, to start with, I have a target antenna and only if the transmitter is aimed to it and a code being sent, the reciever should be able tell if the transmitter was aimed at it.



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    Re: narrow beam antenna and low sensitivity receiver

    at 2.4 GHz you would need a large dish in excess of 3 metres to get a narrow ( less than 5 degree) beamwidth
    conversely, at 24GHz, a 4 degree beamwidth is achieveable with a dish of ~ 1 metre

    Im sure some one here knows the maths for working that out

    You havent really given us all much to go on to try and help you. How about explaining your project a bit more
    You are NOT going to achieve the narrow beamwidths of a laser beam when working at RF microwave freqs

    Dave



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    Re: narrow beam antenna and low sensitivity receiver

    Quote Originally Posted by davenn View Post
    at 2.4 GHz you would need a large dish in excess of 3 metres to get a narrow ( less than 5 degree) beamwidth
    conversely, at 24GHz, a 4 degree beamwidth is achieveable with a dish of ~ 1 metre

    Im sure some one here knows the maths for working that out

    You havent really given us all much to go on to try and help you. How about explaining your project a bit more
    You are NOT going to achieve the narrow beamwidths of a laser beam when working at RF microwave freqs

    Dave
    ok, here's the complete idea. There is a target at some distance (1m to 100m) from site 'A'. The target has a sensor which can detect some form of energy coming from a targeting device. At site 'A' there will be a targeting device emitting some form of energy. If the target and the targeting device come in a straight line, the target senses the energy is 'hit'.

    To do this, initially, I thought of using a laser, but in sunlight it wont work due to saturation of the sensor. So instead I thought of using a highly directional antenna. So, can anyone help me?

    Thank you.



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    Re: narrow beam antenna and low sensitivity receiver

    Read about monopulse antennas. It is easier to measure angles than make narrow beam. Maybe it is good solution for you. Only need to make mixer for monopulse phase extraction.



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    Re: narrow beam antenna and low sensitivity receiver

    Quote Originally Posted by jayanthyk192 View Post
    ...................
    To do this, initially, I thought of using a laser, but in sunlight it wont work due to saturation of the sensor. So instead I thought of using a highly directional antenna. So, can anyone help me?

    Thank you.
    should be quite easy with lasers and the appropriate optical filters, after all police LIDAR's work over 500 metres or so with no problems
    You are not going to produce narrow enought beamwidths over ~100 metres with easily available RF products

    cheers
    Dave



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    Re: narrow beam antenna and low sensitivity receiver

    I agree, forget any RF ideas unless you want to get really complicated, very fast.

    Use an IR LED, pulsed to carry some identifying data if necessary, place it in the center of a small parabolic reflector, maybe a flashlight 'head' or bicycle 'headlight' reflector. Do the same at the receiving end. You should easily achieve 100m range and a narrow overall beam width. Many TV remote control LEDs/sensor work over 10m without any reflectors at all and the combined extra gain at each end will dramatically increase the range you can achieve. With suitable shielding from direct sunlight it should work fine. Most IR receivers have built in light filters which eliminate most of the effects of ambient light anyway.

    Caution: If you use cheap TV remote control LEDs and IR receiver modules, you will find they will not work as expected unless you modulate the light beam. Don't drive the LED with DC, use a square wave at ~38KHz (or ~56KHz if you use a HF detector). The reason is that to improve immunity to other light sources, the receiver will have a built in filter circuit, designed to reject anything far away from it's center frequency (usually 38KHz) so a simple steady light beam will not make it respond.

    If you really want to use RF, look at using Doppler modules at either 10GHz or 24GHz. You can achieve reasonably narrow beams by using horn antennas but you may have difficulty discerning a break in the signal because at these frequencies, objects tend to reflect the signal and it can find an alternative route to the receiver.

    Brian.
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    Re: narrow beam antenna and low sensitivity receiver

    First of all, thank you all for the help.

    Quote Originally Posted by Terminator3 View Post
    Read about monopulse antennas. It is easier to measure angles than make narrow beam. Maybe it is good solution for you. Only need to make mixer for monopulse phase extraction.
    I'll read about it, but as betwixt says, it's getting complex as it is, I'm not able to get ready-made stuff in RF

    Quote Originally Posted by davenn View Post
    should be quite easy with lasers and the appropriate optical filters, after all police LIDAR's work over 500 metres or so with no problems

    cheers
    Dave
    Are you sure they work well in sunlight? if yes, what kind of sensor is used in the LIDAR gun? I'm not able to get info on that.

    Quote Originally Posted by betwixt View Post
    I agree, forget any RF ideas unless you want to get really complicated, very fast.

    Use an IR LED, pulsed to carry some identifying data if necessary, place it in the center of a small parabolic reflector, maybe a flashlight 'head' or bicycle 'headlight' reflector. Do the same at the receiving end. You should easily achieve 100m range and a narrow overall beam width. Many TV remote control LEDs/sensor work over 10m without any reflectors at all and the combined extra gain at each end will dramatically increase the range you can achieve. With suitable shielding from direct sunlight it should work fine. Most IR receivers have built in light filters which eliminate most of the effects of ambient light anyway.

    Caution: If you use cheap TV remote control LEDs and IR receiver modules, you will find they will not work as expected unless you modulate the light beam. Don't drive the LED with DC, use a square wave at ~38KHz (or ~56KHz if you use a HF detector). The reason is that to improve immunity to other light sources, the receiver will have a built in filter circuit, designed to reject anything far away from it's center frequency (usually 38KHz) so a simple steady light beam will not make it respond.

    If you really want to use RF, look at using Doppler modules at either 10GHz or 24GHz. You can achieve reasonably narrow beams by using horn antennas but you may have difficulty discerning a break in the signal because at these frequencies, objects tend to reflect the signal and it can find an alternative route to the receiver.

    Brian.
    I once worked with these 38KHz ir receivers, they worked well indoors, but in sunlight they got saturated and wouldn't work at all even when pointed directly to it,from a close distance. I tried googling out the shielding methods, but none of them were meant to work in direct sunlight.



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    Re: narrow beam antenna and low sensitivity receiver

    How about newly available bright LED used for traffic lights? Those even do not use any caps to protect from daylight. Such LEDs on black surface looks very black when turned of and very red/greenish when on. Even my mobile phone can see this thing very clear in a sunny day.



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    Re: narrow beam antenna and low sensitivity receiver

    Are you sure they work well in sunlight?
    of course they do, cops don't confine their speed trap duties to cloudy days ;)

    Dave



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    Re: narrow beam antenna and low sensitivity receiver

    Quote Originally Posted by Terminator3 View Post
    How about newly available bright LED used for traffic lights? Those even do not use any caps to protect from daylight. Such LEDs on black surface looks very black when turned of and very red/greenish when on. Even my mobile phone can see this thing very clear in a sunny day.
    Can you suggest any sensor that has a CMOS sensor like a cell phone camera?



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    Re: narrow beam antenna and low sensitivity receiver

    Can you suggest any sensor that has a CMOS sensor like a cell phone camera?
    I am not sure it can be used for data transmission.. Just a guess on diodes.
    How about using laser? There are some projects on the net of making rs-232 data line using cheap $2 laser pen. With all details on sensor and schematics

    for example : http://www.qsl.net/n9zia/wireless/laser/laser.htm



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    Re: narrow beam antenna and low sensitivity receiver

    Quote Originally Posted by Terminator3 View Post
    I am not sure it can be used for data transmission.. Just a guess on diodes.
    How about using laser? There are some projects on the net of making rs-232 data line using cheap $2 laser pen. With all details on sensor and schematics

    for example : http://www.qsl.net/n9zia/wireless/laser/laser.htm
    These things work good indoors but , don't work at all out doors during the day



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    Re: narrow beam antenna and low sensitivity receiver

    Your original description suggests all you are trying to do is see if the beam is broken or not. Optical methods are simple and cheap. If you use small parabolic reflectors as I suggested, then mount them in a short opaque tube it will eliminate all but light from a forward direction. Unless the receiver points directly at the Sun (unlikley if it's a point-to-point link) it should work.

    Brian.
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    Re: narrow beam antenna and low sensitivity receiver

    Quote Originally Posted by betwixt View Post
    Your original description suggests all you are trying to do is see if the beam is broken or not. Optical methods are simple and cheap. If you use small parabolic reflectors as I suggested, then mount them in a short opaque tube it will eliminate all but light from a forward direction. Unless the receiver points directly at the Sun (unlikley if it's a point-to-point link) it should work.

    Brian.
    I think I'll try out what you said and see what happens. Thank you all for the help.



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