Frequency hopping useless when listening with SDR

[szangvil]

When I use SDR, I can see all the hops. It's true that I can't predict the hopping sequence, but does it really matter? If I see and record each hop, I have all the information I need to read the data, assuming I know the modulation.

Does it make sense?


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[eorange]

You'd also need to know the order in which the hops arrived. Otherwise, you'd be assembling a jigsaw puzzle.

 

[szangvil]

I can see the order they arrive on the FFT waterfall.


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[szangvil]

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[prcguy]

If you have a receiver for all or most channels in a frequency hopping scheme then you can hear unencrypted traffic. First the transmitter has to transmit long enough for you to log all the freqs then you can program into your receivers.

SINCGARS and some other frequency hopping radios can also add a layer of encryption with Type 1 being available for SINCGARS and your not going to hear any of that traffic. The frequency hopping is more for anti-jamming and less for evasion.
prcguy

 

[SteveSimpkin]

If you have a receiver for all or most channels in a frequency hopping scheme then you can hear unencrypted traffic. First the transmitter has to transmit long enough for you to log all the freqs then you can program into your receivers.
prcguy

I use the "AUX VFO" Plugin for SDR# to create multiple receivers on the same RTL-SDR dongle.
Обновлен плагин дополнительного радиоканала "Aux FVO"

 

[fourthhorseman]

I use the "AUX VFO" Plugin for SDR# to create multiple receivers on the same RTL-SDR dongle.
Обновлен плагин дополнительного радиоканала "Aux FVO"

+1 ...works great,,I use it with great results..just have a fast machine

 

[eorange]

The frequency hopping is more for anti-jamming and less for evasion.

Wouldn't it still be susceptible to jamming if you smeared junk across 5 MHz of bandwidth (for example?)

 

[N9PBD]

Wouldn't it still be susceptible to jamming if you smeared junk across 5 MHz of bandwidth (for example?)

The wider your spread your jamming signal, the lower your average power is, and eventually it becomes easy to 'burn through' the jamming. Unless you have an unlimited power budget, or are sitting right on top of the receiving parties (both ends), you are going to have a much more difficult time jamming a 5 MHz wide swath. Remember, even if we're talking about 25 KHz wide voice channels, that's 200 channels you have to cover in 5 MHz.

 

[szangvil]

I understand the use of FHSS for interference immunity.
My interest is to intercept the data.

For example, I have a 433Mhz SiK1000 radio. I can configure it to use as few as 5 channels and as much as 64 channels. In both situations, I can see all the hops using the RTL-SDR sampling at 2.4Msps.

So FH is not capable of "hiding" the data.

Is it possible to predict the hopping sequence after seeing it for a few minutes? Or is it totally random?


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[RFI-EMI-GUY]

Build a table to cross reference time to the channelnreceived. If the sequence is repeated, all you need to do is figure how ti synchronize the sequence.

 

[prcguy]

As mentioned, if you have a cheap jammer that is just using broad band noise, then widening its band width puts less and less power on a specific frequency to be jammed making it much less effective. For example, if the frequency hopping radio uses a 10KHz wide FM channel and you have 100w of jamming power spread over 10MHz, then there is only about 100 miliwatts of jamming power available in any given 10KHz segment. Gee, I hope I got that right....

Any modern purpose designed military grade jammer is smart and has receivers that help analyze the signal to be jammed so it can maximize the pain to the signal being jammed. Also, most modern frequency hopping military type radios like SINCGARS, Havequick, etc, will usually hop over more than a 5Mhz spectrum.
prcguy

Wouldn't it still be susceptible to jamming if you smeared junk across 5 MHz of bandwidth (for example?)