[Hackrf-dev] Help and Support
Chuck McManis
chuck.mcmanis at gmail.com
Fri Jan 1 20:40:04 EST 2016
Here is a fun link http://www.afar.net/tutorials/900-mhz-versus-2.4-ghz/
which has some more information on 2.4 over distance.
But the important point here is not that you cannot create an antenna setup
that would let you pick up a 2.4Ghz signal at a long distance, but that
with a generic omni-directional one, there is a much much greater chance
you're seeing something nearby.
On Fri, Jan 1, 2016 at 4:18 PM, pete M <petem001 at hotmail.com> wrote:
> just to tell you that I have 2.4 ghz kinks that run over 4 km on normal
> wifi power level. and I have one that is over 34 km on just 3dm more then
> normal wifi power.. And we have humidity level around here that are around
> 70% at a minimum in the sommer/ winter and way more in the spring and
> automn. your explanation of the absorbtion of a 2.4 ghz signal need to be
> revisited.
>
> Sent from my iPad
>
> On Jan 1, 2016, at 4:38 PM, Chuck McManis <chuck.mcmanis at gmail.com> wrote:
>
> Srini, you have remarked about this several times over the last year and
> while appreciate your enthusiasm I think this comment:
>
> > It seems , they don't understand about Radio and 2.4 GHz
> Might hit a bit closer to home. It would suffice it to say that *YOU*
> don't understand about Radio and 2.4Ghz and that is why you don't see the
> obvious way to answer your own questions, and why we cannot answer them.
>
> 2.4Ghz is absorbed by water, because the water molecule forms a small
> dipole antenna of the correct length. That is why it is used in microwaves
> because it heats the water and that hot water heats the rest of the food.
> It is also why it is rarely used for long range communication, as the air
> has moisture in it which absorbs the signal, so not only are you fighting
> the inverse square law you're fighting atmospheric absorption. When it *is*
> used to send a signal more than a mile it is done so with a highly
> directional antenna pointing at another highly directional antenna on the
> receiving end.
>
> If you are seeing *any* sort of bump in the 2.4Ghz band, the source has to
> be less than a mile away and probably less than 1000 meters (or 1km). So
> what ever it is you're worried about, it is literally right next to you.
> Second 2.4Ghz is *HIGHLY* directional, it doesn't bounce much and bounces
> get double absorption so using any sort of directional antenna and a bit of
> geometry you could exactly pin point any *SOURCE* of 2.4 ghz power. And in
> my experience once you look at the thing sending out the RF energy you now
> exactly what it is trying to do.
>
> So build one using a potato chip can
> <http://www.makeuseof.com/tag/how-to-make-a-wifi-antenna-out-of-a-pringles-can-nb/>
> (or buy
> <http://www.amazon.com/USB-Yagi-directional-Antenna-802-11n-2200mW/dp/B003LLS5JI>)
> a directional WiFi antenna, hook it up, and rotate it around until your
> mystery signal peaks. Note your GPS coordinates and the angle with a good
> compass. Then drive 500 meters in any direction and do that again, then 500
> meters in a *different* direction and do it a third time. (the protects
> against you accidentally picking a direction that is in line with the
> transmitter). Now take a map, and put your protractor on it, mark your tree
> measurement points and the angle. Draw lines out from the point. They will
> cross at the point where the transmitter is, go there. Look at the
> transmitter and what ever it is will be clear. If it is moving then that
> would be another good clue for you.
>
> But here is the thing, you will never figure out what this is just by
> observing a signal, you have to go look at it.
>
> --Chuck
>
>
> On Fri, Jan 1, 2016 at 12:23 AM, Srinivasan T <tsvs.lc at gmail.com> wrote:
>
>> Hi There,
>>
>>
>>
>> I detected unknown RF at 2.4 GHz which is not Wi-Fi.
>>
>> This RF is not Wi-Fi, Bluetooth or Microwave, It has different FFT
>> pattern, waterfall, and sound signature.
>>
>> This signal also deliver Wi-Fi packets to make people believe it is Wi-Fi
>> packets.
>>
>>
>>
>> I use AirMagnet XT - 2.4 GHz and the software also detected unknown
>> interference.
>>
>> Attached my analysis document.
>>
>> *https://mega.nz/#!YwplVCCT!Acbe00paHk3dLJuf04B5zSBifSw0-bHz5IciiNLgQwY
>> <https://mega.nz/#!YwplVCCT!Acbe00paHk3dLJuf04B5zSBifSw0-bHz5IciiNLgQwY>*
>>
>>
>>
>> *Please see following pages for quick understanding :*
>>
>> 1. Page 18-19 : Conclusions
>>
>> 2. Page 43-46 : This page contains analysis of Radio
>> Sound from 3 aspects : Sound Track, Sound Wave Form,
>>
>> Sound WaterFall pattern.
>> We can see that huge difference between Wi-Fi 2.4 GHz sound and unknown
>> Radio Signal
>>
>> 3. Page 47-51 : This external signal cause wifi
>> fluctuations. Page 47 contains sample Wi-Fi signal from US which is really
>> normal.
>>
>> Page 50, using
>> AirMagnet XT ( 2.4 GHx spectrum analyzer ) we can see that the external
>> interference cause nearly 10 channels
>>
>> affected. This is
>> abnormal interference.
>>
>> 4. Page 52 : *Relation of RF to human brain
>> frequency*
>>
>> 5. Page 61 : Video as reference, one of
>> video :
>>
>>
>>
>> * Unknown RF at 2.4 GHz reaction with human body with EEG *
>>
>> http://sendvid.com/dofuepqn
>>
>> Details : This video shows the waterfall images. Each
>> time we see set lines, the individual
>>
>> will feel the reaction to body which not able to show to
>> any other people. Please see EEG
>>
>> window at right side at time 6.20 - 6.25 , 6.30-6.40,
>> 6.50 - 6.55. The spike on EEG is
>>
>> trigger by external factor and the individual can feel it.
>>
>> ( other pages
>> as supporting analysis )
>>
>>
>>
>> I reported this issue to 3 RF spectrum managers :
>>
>> 1. iDA - Singapore
>>
>> 2. MCMC - Malaysia
>>
>> 3. Balmon - Indonesia
>>
>>
>>
>> It seems , they don't understand about Radio and 2.4 GHz
>>
>>
>>
>> If anyone could help with more data will be much appreciated or anything
>> else.
>>
>>
>>
>> Regards
>>
>>
>>
>> Srinivasan T
>>
>>
>>
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>>
>>
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