Wireless Video Camera and Interference

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Victor43

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I don't know if this is the correct site for the following questions that I have. If this is not the right site please let me know where I might find a better site for my questions and please accept my apologies.

I would like to know if anyone might be able to help me understand why there would be any interference between two wireless video cameras when placed fairly spaced apart ? If the cameras operate on distinct and exclusive frequencies then why should there be any problems should I wish to install say 30 of these cameras all wireless all in the same building ?

Any suggestions or comments would be appreciated.

Thanking

Victor
 

are these from the same model line? same brand?

are you sure the IP addresses are unique?
 


Most wireless cameras have a frequency selector switch, with 2 or 4 positions, to get rid of an interference from another such device nearby If you read more about the 2.45 GHz band, you will find that there are several channels depending on country standard. As FM is used to transmit he TV plus audio, the width of each spectrum exceeds the "nominal" channel width, and interference occurs.
Using 30 wireless cameras close to each other is a crazy idea and more crazy is that the transmitters and receivers intentionally use only simple antennas, whips or patches, without any directivity. Forget about this idea-it cannot and will not work! Use cables to send video signals to separate receivers (monitors). You will waste time and money and only generate interference.
There are special multi-channel TV wireless systems on the market, but their cost is prohibitive.
 

kam1787 said:
are these from the same model line? same brand?

are you sure the IP addresses are unique?
Click to expand...

Thank you for your reply. These are custom designed chinese made wireless pinhole video cameras. They are exactly the same except for the frequency they operate at. So basically they range from 2.4.1-2.4.100 and so on.

They are not IP based cameras.
 

kam1787 said:
are these from the same model line? same brand?

are you sure the IP addresses are unique?
Click to expand...

Yes they are the same brand and make and model. However they operate on slightly different frequency. If this is what the manufacture states for the specs of the cameras then why should it not be possible to have say over 40 of them in the same building ?

Thanks for the reply.

Victor
 


Thank you for the informative reply. These cameas actually only transmit the picture or video not audio. Audio was not a requirement at the time. If this is the case then does the bandwidth of the signal still exceel the spectum bandwidth as set out in the standard of 2.4 band ?

Thanking you

Victor
 

my mistake! I assumed they were WiFi.

Ask yourself a question - why does the FCC not group FM radio stations closely together in frequency when the stations are in the same geographic area?
 

slightly different freq ... NO it doesn't work that way, each channel for a start is going to be ~ 8MHz in bandwidth
and you are not going to be able to use 2 adjacent channels

Because you would need 40 different channels spaced far enough apart so as not to cause co-channel interference

Dave

- - - Updated - - -

The ONLY ways you will be able to do this with that many cameras is with hard wired cameras either...
1) video over coax cable ... lossy on anything over ~ 50ft
or
2) IP cameras

Dave
 


The FM spectrum does extend over the "frame" even if the audio is not included. The whole problem if you need to operate 30 cameras ( often if they are two or more) in a limited space like a building is that the spectrum frame is limited, and that the antennas used do not separate the beams to prevent interference among channels.

A possible solution is to utilize the frequency band around 60 GHz or 72-84 GHz where there is room for the needed number of channels, and use directional antennas to achieve the inter-channel isolation. There are new fast data links using digital IR transmission but I am not sure if commercially available. If you can modulate the video signal on a fiber, the cabling can be done much easier and without the interference. Possibly at the lowest cost, too.
 

it is most likely an FM transmitter. FM modulation is fairly immune from adjacent channel jamming, but not totally.

So what happens is a receiver is trying to receive transmitter 1, but transmitter 2 on a different frequency is momentarily too big in amplitude that it drowns out the other desired signal. Once that happens, the circuitry that detects the FM modulation gets confused, and sends out analog noise, or digital bit errors.

So the key is first, set the two transmitters at the farthest apart frequencies. If it has a switch for 4 frequencies, for instance, set one to 1, the other to 4.

Then try to position the receive antenna to accentual the desired antenna.

If that all does not work, then u are going to have to go inside the receiver, and try to add additional filtering to reject the undesired signals from reaching the demodulator. Often there is a crude IF filter than could be replaced by a ceramic bandpass filter at the IF frequency.
 

Victor,



Depending on the chipset CODEC used of these cameras, you can really expect different noise immunity.
Please post here more informations about these devices.


+++
 


@davenn Thanks for the frequency bandwidth explanation. So from what I understand your saying that each frame that the transmitters modulates takes about 8MHz in bandwidth correct ? So why cannot the manufacture not design the modulator so that the there is adequate spacing providing adequate bandwidth ?

Thanks

- - - Updated - - -


Thank you for your reply. I am starting to understand your point. However it will not be possinble to use directional antennas because it is not know in the next site where the locations will be where the cameras will need to be installed. This simply will not be possible for our application.

The 2.4Ghz bandwidth also is much more easy for the manufacture to deploy or use since it is a very common ground for many wireless cards and the like. So what I am saying is that any laptop with the right software can pickup up the video signal.

Hope you can understand our application.

Victor

- - - Updated - - -

andre_teprom said:
Victor,



Depending on the chipset CODEC used of these cameras, you can really expect different noise immunity.
Please post here more informations about these devices.


+++
Click to expand...

Thank you for your reply. Would you indicate exactly what other details you would like to know about the transmitter or receiver ?

Victor
 
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Victor,


Some digital encoders\decoders works differently, bringing different performance on image reconstruction facing to noise interference.
Than, what I wish advice is that perceived noise is also related to codec applied.

Once you gave no one informations about brand or manufacturer of these cameras, is not possible to evaluate how much codec represents.

+++
 


he never said they were digital, so no codec is involved

actually victor has never said if they were or were not analog either .... so far that has been the assumption

Dave
 

davenn said:
he never said they were digital, so no codec is involved

actually victor has never said if they were or were not analog either .... so far that has been the assumption

Dave
Click to expand...


Regardless the cause of interference, based on your assumption, it is really expected less ability of these cameras to deal with mutual noise effects.


+++
 

davenn said:
he never said they were digital, so no codec is involved

actually victor has never said if they were or were not analog either .... so far that has been the assumption

Dave
Click to expand...

Thanks for the reply.

To my best of knowledge these models of cameras transmit a digital signal not analog. I have a question to ask all of you. Would it be possible to ask the manufacture if the following is possible. Lets say you have a rule that only one or two cameras can transmit at a time while the others are on standby meaning that they are not transmitting their signal ? However the receiver can easily send a "start sending" signal for any of the other 40 cameras while turning off the transmit signal of the video that is currently transmitting. So basically you don't have all 40 of the cameras transmiting their signal all at once. Are there any other ways getting around the frequency bandwidth limitation kind folks have described here ?

Does the above make sense and can it work ?
 

Hi Victor,


This approach based on management of colision avoiding seems to be perfectly feasible, such as in a TDM ( Time Division Multiplexing ).
However, in order to guarantee no mutual interferente, a timed external system must be implemented to perform synch of channels.

( it means that only one camera would be turned on at a time )


+++
 

kam1787 said:
my mistake! I assumed they were WiFi.

Ask yourself a question - why does the FCC not group FM radio stations closely together in frequency when the stations are in the same geographic area?
Click to expand...

THank you for your reply. Your exmaple explains my situation well. Then would it not be possible to design the cameras so that they use a less frequently used band but one that has sufficient room for spacing between adjacent channels. Jiripolikka mentioned it in his post that the frequency band of 60 GHz or 72-84 GHz has enough room for the number of channels needed including adequate room for spacing.

Thanks to everyone for the really helpful replies.
 

The 60GHz or 72-84GHz needs line of sight, that means between the tx and the rx there should be no obstacle. Is it possible for your applications?
If you want to install them into a builidng, there are some walls between them, so this idea seems can't work any more.
 


Thank you for your reply. Yes you are right the deployment of these cameras will have obstacles (walls and floors and so on) between the transmitter and receiver. I would like to ask then one final question before closing this thread.

I had asked whether it is possible to have one video cameras transmitting its picture at one time only and the answer above was yes. But now I would like to know whether it would be possible to use the 2.4GHz band on a group of these cameras ? So say there are 4 floors inside the building and each floor has 10 video cameras installed. So would it be possible to switch between each group of 10 video cameras showing the video of any one of four groups ? So there will be only 10 video cameras broadcasting their picture to the receiver at any given time.

Thanks again
Thanks
 
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