Whether it appears as noise or not, it would interfere with normal traffic and be investigated very quickly. That doesn't make it very 'covert' !
You certainly can't use cell base stations as repeaters, they don't work that way at all and it would be very difficult to disguise another transmission so it could 'sneak through' un-noticed.
Brian.
I worked on the design of cell base stations for a major US comms company although I am no longer working in that particular field of electronics.
I'm not really sure what your intention is. To actually use the normal cell traffic to hide a cell transmission or to hide another 'non-cell' transmission amongst the existing carriers.
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Brian.
sure. they have been doing that with intellsat for decades.
you need a spread spectrum signal and a transmit power that keeps it under the "noise floor" of the environment, which is higher than thermal noise. Also the spread spectrum signal has to be devoid of any modulation frequency peaks...I mean really devoid of them.
It is easier to do it for satellite, since the range is pretty much a constant...i.e. wicked long. for a cell phone the range can be anywhere from 200 feet to 30 miles....so making sure the spreading signal is below the noise floor is difficult technically
I've never seen a 'tuned' IC that works on a particular frequency. All the ones I have seen or used rely on external tuned circuits or resonators, in other words the IC is generic and no amount of reverse engineering will expose anything other than a broad range of frequencies it might be optimized for.It has been said that it is impossible to discover the frequency(s) being used by way of reversing the integrated circuit die. Any ideas on how we can isolate these "hidden RF frequencies" ? Is it possible to determine the range of frequencies being used if the IC is using some kind of pass band filter ?
I've never seen a 'tuned' IC that works on a particular frequency. All the ones I have seen or used rely on external tuned circuits or resonators, in other words the IC is generic and no amount of reverse engineering will expose anything other than a broad range of frequencies it might be optimized for.
Typically, ICs for low power data transmission use a resonator and PLL to multiply it's frequency up to final carrier rate. When viewing an actual module, the frequency is fairly easy to guess, it will typically be the nearest multiple of the resonator frequency to the wavelength of the quarter wave antenna. Of course anyone looking on a spectrum analyzer would spot it and be able to read the frequency anyway.
I think most satellites use linear transponders so predictably dispersing the RF energy on the uplink and reconstructing it from the downlink is possible but given the crowded cell frequencies and need to work point-to-point would make it far harder.
Brian.
1. transmit power that keeps it under the "noise floor
2. devoid of any modulation frequency peaks
How can it communicate then?
Brain just clarify the above comments. You are saying that it is rare to find a RF device (Tuned IC) using just a single frequency but rather a range ? Secondly you said "When viewing an actual module, the frequency is fairly easy to guess" yes ? Does this imply that by way of decapsulation and the study (some reversing) of the tuner found in a RF device IC the range of used frequencies can be determined yes ?
What I mean is that to accurately manufacture a silicon device that oscillates at a specific frequency is almost impossible.
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