4 ms·

How do you disguise a radio transmitter? It's about as futile as disguising a searchlight.

by owl57 6y ago

baybal2 6y ago
No so fast. China tried to crack down on VSAT terminal possession for years. Up to no, to a very little effect. Brown trucks with gobs of antennas are the guys who are tracking them down, some Chinese 3 letter service.
lb1lf 6y ago
While a transmitter is indeed to a first approximation a beacon screaming 'I'm here!', do keep in mind that these antennas are highly directional, and while there will be side lobes, you basically need to be in the beam path to even detect it's there - complicating matters significantly. Besides, the antenna itself is rather small, and can be hidden inside just about any structure transparent to RF in the relevant frequency bands - say, a seemingly innocuous water cistern on the roof, for instance.
hansor 6y ago
1. Narrow beam antenna (such as satellite antenna) does NOT propagate signal arround it (OMNIdirectional antennas does that). It's almost impossible to detect it unless you fly directly over the beam. Think about it as laser beam. 2. It is possible to build verious kinds of covert antennas. Radio amateurs do that all the time. Just google the term "stealth ham radio"
- owl57 6y ago
  1. Is it expensive for TLAs to deploy drones for exactly that if the practice becomes popular? They won't even need many actual detecting drones: if they look the same as regular surveillance drones, which are already up in the sky in times of unrest, people will probably hesitate to use their transmitters.
- wongarsu 6y ago
  > Think about it as laser beam. But if you shine a powerful laser beam into the sky it is visible from pretty far away. It's highly focused, but also gets scattered a lot by the atmosphere.
  - hansor 6y ago
    Think about it as inivisible laser beam in terms of beam width. We are talking here 2mm wave with very directional antennas - its very hard to detect it. That's actually how spies send data back over the satellites: >Unlike with SW signals, a radio signal to a satellite is very difficult to intercept and trace, as the waves are 'beamed' straight up rather than all around. https://www.cryptomuseum.com/spy/rs804/index.htm https://www.cryptomuseum.com/spy/rs804/index.htm
    - ajsnigrutin 6y ago
      What? There's no way to send a 2mm (width) wave. Yes, parabolic antennas have very high gains in one direction, but they're far from '2mm' and far from 'invisible'. A helicopter with the right equipment flying over urban areas would have an easy job finding them and even pointing out the approximate location (eg. a building) where they're located. If the antenna was inside a huge apartment building, it would be hard to find the right apartment, if the transmitter was turned off, but with single family buildings, it would be easy. Ham radio operators hide and then look for hidden transmitters for fun, so it's not that hard, especially with a budget that is given to the police.
      - hansor 6y ago
        >There's no way to send a 2mm (width) wave. You are very wrong sir. https://en.wikipedia.org/wiki/2-millimeter_band https://en.wikipedia.org/wiki/2-millimeter_band >A helicopter with the right equipment flying over urban areas would have an easy job finding them. That is not true. Helicopter would need to fly RIGHT into such directional and tiny beam. Which is nearly impossible to do in huge city. Even when flying 2m next to it, you would likely not detect it. That is the reason why CIA had so much problem with pinpointing Iridium satellite phones back in Colombia in the 90's.
NortySpock 6y ago
Put it in a (plastic) box shaped like something else? "Yeah, that's my 'compost bin'"
- dragonwriter 6y ago
  That's a nice visual disguise but it doesn't do much to help when someone with radio direction finding gear starts looking for unauthorized transmitters on the frequency it operates on.

How do you disguise a radio transmitter? It's about as futile as disguising a searchlight.

by owl57 6y ago

How do you disguise a radio transmitter? It's about as futile as disguising a searchlight.

No so fast. China tried to crack down on VSAT terminal possession for years. Up to no, to a very little effect. Brown trucks with gobs of antennas are the guys who are tracking them down, some Chinese 3 letter service.

lb1lf 6y ago

While a transmitter is indeed to a first approximation a beacon screaming 'I'm here!', do keep in mind that these antennas are highly directional, and while there will be side lobes, you basically need to be in the beam path to even detect it's there - complicating matters significantly. Besides, the antenna itself is rather small, and can be hidden inside just about any structure transparent to RF in the relevant frequency bands - say, a seemingly innocuous water cistern on the roof, for instance.

hansor 6y ago

1. Narrow beam antenna (such as satellite antenna) does NOT propagate signal arround it (OMNIdirectional antennas does that). It's almost impossible to detect it unless you fly directly over the beam. Think about it as laser beam. 2. It is possible to build verious kinds of covert antennas. Radio amateurs do that all the time. Just google the term "stealth ham radio"

owl57 6y ago
1. Is it expensive for TLAs to deploy drones for exactly that if the practice becomes popular? They won't even need many actual detecting drones: if they look the same as regular surveillance drones, which are already up in the sky in times of unrest, people will probably hesitate to use their transmitters.
wongarsu 6y ago
> Think about it as laser beam. But if you shine a powerful laser beam into the sky it is visible from pretty far away. It's highly focused, but also gets scattered a lot by the atmosphere.
- hansor 6y ago
  Think about it as inivisible laser beam in terms of beam width. We are talking here 2mm wave with very directional antennas - its very hard to detect it. That's actually how spies send data back over the satellites: >Unlike with SW signals, a radio signal to a satellite is very difficult to intercept and trace, as the waves are 'beamed' straight up rather than all around. https://www.cryptomuseum.com/spy/rs804/index.htm https://www.cryptomuseum.com/spy/rs804/index.htm
  - ajsnigrutin 6y ago
    What? There's no way to send a 2mm (width) wave. Yes, parabolic antennas have very high gains in one direction, but they're far from '2mm' and far from 'invisible'. A helicopter with the right equipment flying over urban areas would have an easy job finding them and even pointing out the approximate location (eg. a building) where they're located. If the antenna was inside a huge apartment building, it would be hard to find the right apartment, if the transmitter was turned off, but with single family buildings, it would be easy. Ham radio operators hide and then look for hidden transmitters for fun, so it's not that hard, especially with a budget that is given to the police.
    - hansor 6y ago
      >There's no way to send a 2mm (width) wave. You are very wrong sir. https://en.wikipedia.org/wiki/2-millimeter_band https://en.wikipedia.org/wiki/2-millimeter_band >A helicopter with the right equipment flying over urban areas would have an easy job finding them. That is not true. Helicopter would need to fly RIGHT into such directional and tiny beam. Which is nearly impossible to do in huge city. Even when flying 2m next to it, you would likely not detect it. That is the reason why CIA had so much problem with pinpointing Iridium satellite phones back in Colombia in the 90's.

NortySpock 6y ago

Put it in a (plastic) box shaped like something else? "Yeah, that's my 'compost bin'"

dragonwriter 6y ago
That's a nice visual disguise but it doesn't do much to help when someone with radio direction finding gear starts looking for unauthorized transmitters on the frequency it operates on.