SpaceEx just launched three government SIGINT satellites that will triangulate any signal in the world. When we say, “triangulate,” we mean, “pairs of satellites use time-difference of arrival (TDOA) to compute a line-of-bearing to the signal-of-interest. Two different lines-of-bearing from two different pairs gives a fix which is projected onto a map.”
Based on this article, we can infer the capability of the Hawkeye receiver.
The first order of business, however, will be catching pirates. Smugglers and other wrongdoers of the high seas regularly turn off their GPS transponders to avoid tracking. Instead, they use satellite phones and CB radios to coordinate with other ships or confederates on land, all of which will whisper to the Hawkeye toasters soaring overhead.
This can detect CB radios from space. What is the FCC specification of CB radio?
The current specification is simply “4 watts output (AM) or 12 watts output (SSB)” as measured at the antenna connector on the back of the radio.
4 Watts is +36 dBm (10*log(4 W/.001 W). With 3 dB antenna gain in an omnidirectional pattern, the effective radiated power is about +40 dBm. CB is in the 11 meter band which propagates very well as a surface wave over the ocean. This satellite measures the component of transmission in the direction of the satellite, which is just as strong as the component towards the shore due to the omnidirectional antennas used by the pirates.
As I said, vertically-polarized 11 meter waves travel very far as a surface wave over the ocean. This phenomenon is even used by certain types of radars called surface-wave over-the-horizon radars to detect and track ships thousands of miles away from coastline. The point is: pirates don’t need a lot of power to communicate with the shore if they know which direction their friends on the shore or at sea are. They can use a combination of a directional antenna such as a vertically-polarized V-antenna or a Yagi and attenuation between the antenna and the power amplifier to reduce the effective radiated power and focus it towards their friends and away from this Hawkeye system. This will reduce the effective radiated power in the direction of the SIGINT system hopefully below its sensitivity or perception threshold.
As you can see from the picture, now the gain towards friends is +12 dBi and therefore the effective radiated power in the direction of friends is +36 dBm (power after the amplifier) + 12 dB = +48 dBm or 63 Watts. This is probably far more power than is needed depending on the range. Power can be further reduced by adding an SMA attenuator between the power amplifier and antenna which reduces the ERP by 1 dB for every 1 dB of attenuation but the power is still focused towards friends as before.
The gain towards the satellite is 20 dB down from the gain at the boresight of the antenna, or -2 dBi. The power radiated in the direction of the satellite is therefore +36 dBm – 2 dB = +33 dBm or 2 Watts. Adding attenuation reduces this further, perhaps below the perception threshold or sensitivity of the Hawkeye receiver. In upcoming posts, we will look at Friis’ transmission equation as a means of modeling susceptibility of transmissions to enemy SIGINT receivers.
In addition to carefully directing and controlling the radiated power, the other thing to do is send short data packets rather than long voice transmissions. The SIGINT receiver is usually sweeping or hopping between bands to search for signals of interest. Information theory explains how a signal must be long enough to charge the filters of a receiver to make it detectable. Thus, the shorter you can make your transmissions, the less likely they are to be detected by a sweeping or hopping SIGINT reciever. Send them during the time that a skywave suffers the worst propagation so that the atmosphere both attenuates transmission to the satellites and adds ionospheric noise. Do not use the sky wave for transmissions such as NVIS because not all power from your transmitter is reflected by the atmosphere. Some is refracted through the atmosphere (think of Snell’s law) and the path through the atmosphere is also to these satellites. Use the ground wave/surface wave.
Finally, ask yourself if you need to radiate at all. The Danes, English, and sea powers of old did not need radios to coordinate maritime operations yet they could rendezvous at planned date and times, even for the right tide for amphibious operations. Similarly, land-based forces were able to do the same thing. Use mission orders instead of the US military’s top-down control to make communication less necessary. Use alternatives to the electromagnetic spectrum for communication if you must communicate. Remember: pigeons were the first type of packet radio.