4 ms·

What you say about locating SW receivers may have been true in the era of superhetrodyne receivers, but today, in the era of direct digital sampling, it's no lo

What you say about locating SW receivers may have been true in the era of superhetrodyne receivers, but today, in the era of direct digital sampling, it's no longer true. Old superhet receivers would leak the LO through the mixer out to the antenna so nearby detectors could deduce where the receiver was and what it was tuned to (assuming a standard IF, which is a fair assumption given the plethora of high-Q 455KHz and 10.7MHz ceramic filters). Nowadays with a good digital receiver, nothing leaks from the receiving antenna.

wkat4242 4y ago
Well yes that's what I said - these days it's less true with the direct conversion (many superhet's around though still!) but SW numbers stations are not really a thing anymore anyway so the solution is a bit late :) And a direct conversion receiver and the computer attached to it can also leak RF. I'm pretty sure equipment these days leaks more RF than in the 80s. And not just RF. People have even been able to determine private keys from the coil whine in the audio sampled across the room from the PC running the crypto! Though I wonder if spies used SDRs (or other direct conversion receivers) earlier than the mainstream for this reason.. On the other hand I've heard spies usually shy away from special electronics because it's a lot harder to explain than a standard holiday shortwave receiver.
- krisoft 4y ago
  > standard holiday shortwave receiver A what now? :) Are you sure that is a lot harder to explain away than literally any computer gizmo looking object? (Today, not in the 70ies)
  - wkat4242 4y ago
    > (Today, not in the 70ies) Exactly, numbers stations were a big thing in the 70s-80s. In those days carrying a SW receiver was pretty standard and almost every country had a world service radio station that people would actually listen to. These days using the internet makes a lot more sense yes, both for tourists and spies. Because spies want to be where the mainstream is to avoid detection.

wkat4242 4y ago

Well yes that's what I said - these days it's less true with the direct conversion (many superhet's around though still!) but SW numbers stations are not really a thing anymore anyway so the solution is a bit late :) And a direct conversion receiver and the computer attached to it can also leak RF. I'm pretty sure equipment these days leaks more RF than in the 80s. And not just RF. People have even been able to determine private keys from the coil whine in the audio sampled across the room from the PC running the crypto! Though I wonder if spies used SDRs (or other direct conversion receivers) earlier than the mainstream for this reason.. On the other hand I've heard spies usually shy away from special electronics because it's a lot harder to explain than a standard holiday shortwave receiver.

krisoft 4y ago
> standard holiday shortwave receiver A what now? :) Are you sure that is a lot harder to explain away than literally any computer gizmo looking object? (Today, not in the 70ies)
- wkat4242 4y ago
  > (Today, not in the 70ies) Exactly, numbers stations were a big thing in the 70s-80s. In those days carrying a SW receiver was pretty standard and almost every country had a world service radio station that people would actually listen to. These days using the internet makes a lot more sense yes, both for tourists and spies. Because spies want to be where the mainstream is to avoid detection.