3 ms·

> Any receiver using the heterodyne principle (this includes most current digital radio modems) is trivially detected by its local oscillator, often to some con

by mlyle 4y ago

> Any receiver using the heterodyne principle (this includes most current digital radio modems) is trivially detected by its local oscillator, often to some considerable range (potentially hundreds of metres). I'm sorry. This is not intrinsic; this is a design choice. Yes, most LOs just care about getting under legal emission masks, but there's nothing to prevent one from bringing it much lower. Further, as I explained: the LO frequency of the LNB for the first conversion is often the exact same frequency as you'd use to downconvert digital TV broadcast. > In the UK, the BBC used to exploit this, with radio detection vans patrolling the streets for unauthorized receivers, to fine people for watching TV without a license. They never found anyone in a way that could be used for prosecution. "A freedom of information act has revealed that TV Detector vans have never to date provided evidence to be used in court against the TV Licence Non-payer, and have therefore never succeeded in enforcing the TV licence." https://en.wikipedia.org/wiki/TV_detector_van https://en.wikipedia.org/wiki/TV_detector_van

retrac 4y ago
It's not intrinsic, no. It's possible to design a receiver with its local oscillator emissions to be down to an arbitrarily low emission standard. (But who actually does that?) And not all reception techniques require a local oscillator at all. Still. My point was merely that with an average radio, which was designed to just not be harmfully interfering, such as typical satellite TV receiver? It's quite possibly lit up like a beacon if you know what to look for.
- mlyle 4y ago
  > with its local oscillator emissions to be down to an arbitrarily low emission standard. (But who actually does that?) Better testing to compliance standards has pushed LOs down way lower than they were in the 40s-60s. We have relatively cheap high quality spectrum analyzers and big integrated measurements. So-- kinda everyone pushes things down pretty low now. > My point was merely that with an average radio, which was designed to just not be harmfully interfering, such as typical satellite TV receiver? Yah-- this LNB looks just like a satellite TV receiver, with the exact same LO frequency. So your rogue downlink looks exactly like something that there's hundreds of innocent versions around. Then a SDR inside your house chooses a different signal from the transponder and gets the data.
  - lazide 4y ago
    In countries this would be a problem in right now, satellite TV is often banned too.
    - mlyle 4y ago
      Satellite TV is exceptionally common in Pakistan, I believe.
      - lazide 4y ago
        And Iran. Still banned though. [https://gulfnews.com/world/asia/pakistan/government-bans-import-of-satellite-dish-equipment-1.212305 https://gulfnews.com/world/asia/pakistan/government-bans-imp...] Of course, so are most drugs in the US.
        mlyle 4y ago
        I believe that receiving state media with state-approved satellite services is A-OK. This is an import ban on unapproved equipment.
        lazide 4y ago
        It’s also legal to take state approved drugs in the US. Point taken though!
        mlyle 4y ago
        The point is, there's a whole lot of (mostly legal) satellite receivers around, so looking for satellite receivers doesn't seem like a great way to spot dissidents immediately.
  - tormeh 4y ago
    Satellite TV receivers are generally frowned upon in authoritarian societies, I believe.

by mlyle 4y ago

retrac 4y ago

It's not intrinsic, no. It's possible to design a receiver with its local oscillator emissions to be down to an arbitrarily low emission standard. (But who actually does that?) And not all reception techniques require a local oscillator at all. Still. My point was merely that with an average radio, which was designed to just not be harmfully interfering, such as typical satellite TV receiver? It's quite possibly lit up like a beacon if you know what to look for.

mlyle 4y ago
> with its local oscillator emissions to be down to an arbitrarily low emission standard. (But who actually does that?) Better testing to compliance standards has pushed LOs down way lower than they were in the 40s-60s. We have relatively cheap high quality spectrum analyzers and big integrated measurements. So-- kinda everyone pushes things down pretty low now. > My point was merely that with an average radio, which was designed to just not be harmfully interfering, such as typical satellite TV receiver? Yah-- this LNB looks just like a satellite TV receiver, with the exact same LO frequency. So your rogue downlink looks exactly like something that there's hundreds of innocent versions around. Then a SDR inside your house chooses a different signal from the transponder and gets the data.
- lazide 4y ago
  In countries this would be a problem in right now, satellite TV is often banned too.
  - mlyle 4y ago
    Satellite TV is exceptionally common in Pakistan, I believe.
    - lazide 4y ago
      And Iran. Still banned though. [https://gulfnews.com/world/asia/pakistan/government-bans-import-of-satellite-dish-equipment-1.212305 https://gulfnews.com/world/asia/pakistan/government-bans-imp...] Of course, so are most drugs in the US.
      - mlyle 4y ago
        I believe that receiving state media with state-approved satellite services is A-OK. This is an import ban on unapproved equipment.
        lazide 4y ago
        It’s also legal to take state approved drugs in the US. Point taken though!
        mlyle 4y ago
        The point is, there's a whole lot of (mostly legal) satellite receivers around, so looking for satellite receivers doesn't seem like a great way to spot dissidents immediately.
- tormeh 4y ago
  Satellite TV receivers are generally frowned upon in authoritarian societies, I believe.