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How to locate source of radio signal?

  1. Nov 1, 2011 #1
    What method is usually used to locate exact place of radio signal source?
    Do exist some type of radio signals, exact place of origin which is completely impossible
    to locate?Well,at least up to few hundreds of feets?
     
  2. jcsd
  3. Nov 1, 2011 #2

    Averagesupernova

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    Most sources can be located exact. However, that is not to say that the same method of detection is used to locate the source starting at a number of miles down to the exact point. Several changes in method may be needed from start to finish. Also, some sources are spread over a large area such as a power line radiating noise from an arc.
     
  4. Nov 1, 2011 #3

    berkeman

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    Here is some background on Radio Direction Finding:

    http://www.homingin.com/

    As ASN says, you can usually find the source exactly, but there are situations that make it more difficult. If you have multi-path issues, that confuses the location of the source.
     
  5. Nov 1, 2011 #4

    sophiecentaur

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    That's a rather misleading statement. There is always an error in measuring anything and the accuracy of bearing for DFing a radio source is very variable. It will depend on the frequency, the receive antenna characteristic and the surroundings of both the transmitter and the receiver - adjacent objects can cause reflections which may cause very significant errors.
    Don't be mislead by the TV and Film scenes where they show, on a screen, a spy moving down the corridor of an office block. Radio signals just don't work like that in practice.

    GPS is a system which uses the highest tech available and that will, on a good day, give you a location accuracy of just a few metres. (yes - I know it's the other way round but the argument still applies.) Locating a low frequency transmitter at a distance could be a very different matter.
     
  6. Nov 1, 2011 #5

    berkeman

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    ASN did mention that lower frequency signal sources are harder to locate with accuracy.

    @Staney514 -- If you are looking for radio signal sources that are hard to locate, look at what the military uses in the field. They obviously do not want some radio sources located easily, because that will draw enemy attention and fire. Two techniques used by the military are frequency hopping and very short transmissions. Each of those make it very difficult (or impossible) to locate the source radio.

    http://en.wikipedia.org/wiki/Frequency_hopping
     
  7. Nov 1, 2011 #6

    sophiecentaur

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    I think the OP would need to be a bit more specific for much more of an answer.
    At the moment it's a bit 'how long is a piece of string?'.
     
  8. Nov 2, 2011 #7

    Averagesupernova

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    Hold it Sophie. You are making quite a few assumptions about what the OP and I have posted. No one has said anything about pointing some magic device around and being able to say something like: "Yep, the source is that room that is 3rd from the end of the building on the north side, 7th floor, in the McDonald building on 5th Street 11 Km west of here." I simply said it can usually be located and mentioned that from the start of the search to the end several different methods of detection may be required. Was there a requirement of not being mobile during the search? I don't think so.
    -
    I would hope anyone with any sense would not think that there is some magical hypothetical device that actually exists based on what I said in my earlier post.
     
  9. Nov 2, 2011 #8

    sophiecentaur

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    It was only the word "exact" that got me going.
    On a forum like this, the very least one can do is follow the conventions and mention accuracy of any measurement.
    I am a bit more skeptical than you are about the likelihood of people realising that real life is not like the movies. There are enough amazing posts to be read on PF which demonstrate just that. Furthermore, the way that mobile phones can be located so well, these days, can only support those misconceptions although, as you and I both realise, the technology involved is quite different.
     
  10. Nov 5, 2011 #9
    Radiolocation has been an important topic in espionage, warfare, and telemetry. Every technique I know of is based upon the interaction between a receiving antenna and the radio wave.

    I've seen two catagories of antennas used for this. One relies upon nulls where the antenna is insensitive to the wave. The round, rotating antennas that one might see in an old war movie functioned this way.

    A catagory of antenna I see used commonly relies upon it's pronounded sensitivity in one orientation. Thus the received signal is most pronounced when the antenna is directed towards the source of the signal.

    In either of these cases, at least two receiving locations must be used to ascertain the location of the signal on a map. If you were searching in space, three locations must be used.

    If you're very interested in telemetry, you might reference hawking and falconry as these sports commonly use the technology.

    Mike
     
  11. Nov 20, 2011 #10
    If military people whould need what is a relatively cheap and easy way to establish radio
    jamming?Could it be done with help of strong electric discharges?Let`s say they would need to jam
    most of MHz and lowest part of GHz spectrum?
    What other ways of radio jamming exist?
     
  12. Nov 20, 2011 #11

    sophiecentaur

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    To 'jam' a radio transmission, you need to produce an interfering signal which has a significant amount of power within the bandwidth of the signal you are trying to jam. If you want to 'blanket' jam all transmissions then you would need a phenomenal amount of transmitter power, covering the whole of the transmission band. To jam 100 channels, you could need 100X the power for jamming just one transmission. Often the jammers have an advantage because they can be trying to jam distant signals with a local transmitter but it is still far better value to target the transmissions you want to jam.

    GHz signals are particularly hard to jam because you need to have your jamming transmitter very near a line connecting transmitter and receiver - because receiving antennae for GHz transmissions tend to be very directional.
     
  13. Nov 20, 2011 #12
    What is the easiest and cheapest way to establish brodband
    radio noise?Spark gap transmitters are good for this?
     
  14. Nov 20, 2011 #13

    sophiecentaur

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    Like I said, you need to know what actual power you need over the WHOLE of the broadcast band.
    You might have the regulatory people knocking on your door too! Or are you just trying to deal with noisy neighbours?
     
  15. Nov 21, 2011 #14

    berkeman

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    Doing this is generally illegal (and can be dangerous, if you interfere with radio traffic for police, firefighters, EMS, etc.). We do not discuss illegal or dangerous activities on the PF. Thread closed.
     
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