3 ms·

> I'm sure a tiny bit of RF leaks out of the LNB Any receiver using the heterodyne principle (this includes most current digital radio modems) is trivially det

by retrac 3y ago

> I'm sure a tiny bit of RF leaks out of the LNB 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). 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. So did the USSR with shortwave receivers, where the penalty was potentially more than a fine. A satellite receiver is the same, in principle.

mlyle 3y 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 3y 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 3y 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 3y ago
      In countries this would be a problem in right now, satellite TV is often banned too.
      - mlyle 3y ago
        Satellite TV is exceptionally common in Pakistan, I believe.
        lazide 3y 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 3y ago
        I believe that receiving state media with state-approved satellite services is A-OK. This is an import ban on unapproved equipment.
        3y ago
nine_k 3y ago
I suppose the heterodyne frequently (the 465 kHz of AM, for instance) can be effectively hidden. Put your whole receiver into a metal enclosure, have a high-pass filter before the antenna connector, and a low-pass filter before the outputs and power connectors. Such a device would likely look peculiar enough to be easily recognizable, though, so you'll need to hide it, possibly inside some innocuous-looking other device or enclosure. The whole setup becomes somehow more involved, but still cheap enough.
- mlyle 3y ago
  > I suppose the heterodyne frequently (the 465 kHz of AM, for instance) can be effectively hidden. Put your whole receiver into a metal enclosure, have a high-pass filter before the antenna connector, and a low-pass filter before the outputs and power connectors. Yes-- and every piece you mention is "quality radio design 101". > Such a device would likely look peculiar enough to be easily recognizable I'm not sure about that. The biggest most suspicious thing is, if they're resourced to investigate everyone with a piece of coax going outside-- where does yours plug into? Of course, if you're really dedicated-- get a satellite TV receiver, empty out the nice metal box, put the receiver inside ;).

by retrac 3y ago

mlyle 3y 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 3y 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 3y 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 3y ago
    In countries this would be a problem in right now, satellite TV is often banned too.
    - mlyle 3y ago
      Satellite TV is exceptionally common in Pakistan, I believe.
      - lazide 3y 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 3y ago
        I believe that receiving state media with state-approved satellite services is A-OK. This is an import ban on unapproved equipment.
        3y ago

nine_k 3y ago

I suppose the heterodyne frequently (the 465 kHz of AM, for instance) can be effectively hidden. Put your whole receiver into a metal enclosure, have a high-pass filter before the antenna connector, and a low-pass filter before the outputs and power connectors. Such a device would likely look peculiar enough to be easily recognizable, though, so you'll need to hide it, possibly inside some innocuous-looking other device or enclosure. The whole setup becomes somehow more involved, but still cheap enough.

mlyle 3y ago
> I suppose the heterodyne frequently (the 465 kHz of AM, for instance) can be effectively hidden. Put your whole receiver into a metal enclosure, have a high-pass filter before the antenna connector, and a low-pass filter before the outputs and power connectors. Yes-- and every piece you mention is "quality radio design 101". > Such a device would likely look peculiar enough to be easily recognizable I'm not sure about that. The biggest most suspicious thing is, if they're resourced to investigate everyone with a piece of coax going outside-- where does yours plug into? Of course, if you're really dedicated-- get a satellite TV receiver, empty out the nice metal box, put the receiver inside ;).