Sudden Radio Silence in High Risk Scenarios

At Boston we’ve ben attacked as a nation by a bomber.

Our prayers and thoughts are with those killed and injured, and their families.

Our heartfelt thank you and admiration goes out to those who responded, especially as they really didn’t know if they themselves were safe from an additional bombing.

From the news one item dealing with RF jumped out – the Cell Phone Network was instantly taken down by authorities to prevent its use as a trigger for any additional bombs.

Bombs, or IEDs (Improvised Explosive Devices) if you prefer, are typically controlled in two ways:

  • Time
  • Trigger

For Time you can imagine the electronic, mechanical, or chemical functional equivalent of a “fuse.”  Once the fuse is lit, the bomb will be set off at a set period of time afterwards.  The timer can be internal or external, but the functional distinction of a Time Bomb is the device is exploded based on Time as the primary criteria.

For Trigger devices there may be manual control (pull a string, a trip-wire, or hit the detonator with an impact), electronic control (wires back to detonator control box),  a conditional control (goes off when stepped on, moved, opened, when wet, or any other a number of sensor based criteria), radio control (think of the door lock button on your car’s key fob, or perhaps its own cell phone or other receiver), or other set-off methods.  The main criteria of Trigger is that external stimulus is needed to set the bomb off.

There are combinations of Time and Trigger – the combinations are endless.

As radio amateurs we’re interested in the Trigger by Radio.  In the Boston case authorities feared/theorized that the cell phone network was a potential Trigger and for safety they shut it down.

In the videos released I didn’t spot any first responders, police, fire or security on radios, though it is unclear if radio silence was being enforced.

Often used in warfare, there are jamming countermeasures that might be deployed, which deny the use of the RF spectrum as a Trigger.  Some variations are intended to set off the RF based Trigger exploding a device from a stand-off situation.

The cowards who did the Boston bombings very likely may have controlled the bombs by cell phone.

In a situation like this bombing one has to reflect if keying up an HT is very smart – at least until the area is searched for additional devices & cleared.  If the enemy has left a tiered pattern of devices the RF from an HT may be the next device’s Trigger.

Temporary self imposed Radio Silence in High Risk Scenarios may be needed until the “all clear” is given.

“Certainly much more will come to light about the remote Cell Phone detonation of the devices, over the next few days and weeks.

Again our prayers and thoughts are with those killed and injured, and their families.



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6 thoughts on “Sudden Radio Silence in High Risk Scenarios

  1. There is one anonymously-sourced report, “a law enforcement official”, that the shutdown was intentional. There are sourced reports that it is an overload.,0,3645612.story

    Earthquakes cause a similar synchronous demand on telephone networks. Even landlines are severely overloaded for hours after a disaster like that.

    So telephone outages are completely normal and don’t need explanations involving the authorities. The populace is quite capable of taking out the network with simple demand.

    RF triggered devices might be a hazard, but there was continuous use of HTs on multiple frequencies for hours and hours at the finish line before the explosions. Just look at the video — everyone has a radio.

    • k9zw says:

      Hi Walter K6WRU

      Let’s see what settles out – there are several sources stating that the cell net was downed for security.

      You’re correct that this was an RF rich environment.

      Several sources say it was woking if you made a call from a cell phone outbound, but calls inbound to the area for cell phones were blocked until the area was secured.

      There are a few sources that devices such as these – – were employed.

      We’ll unlikely be given details if they were. Makes good security sense to not fill in these sorts of details.

      It would seem reasonable to expect standard countermeasures to make such gear available.

      In the videos it was clear if anyone was doing an environmental assessment, as another way IEDs have tiered hazards causing additional collateral damage is contamination.

      One set of reports that is concerning is the talk that video analysis quickly showed suspicious activity from a apparently single criminal placing several backpacks in garbage cans.

      Were the camera feeds unwatched?

      A third incident at the library looks related in time, but appears to have been a fire bomb.

      It is also worth mentioning that a Risk/Return analysis of RF prior to clearing the area of additional hazards might weigh heavily on making the contact even with the RF concern.

      It has been reported the Volunteer Hams were evacuated from the scene.



  2. k9zw says:

    It is important to point out that very few have any information beyond the various briefings given to the public.

    Some of the congress critters have spoken about the briefings they have received, which is interesting.

    Again our prayers for the injured and killed.



  3. Chris KK4BRO says:

    There are news reports that the cell system was down, but all of the carriers say those reports are false.

    As for cops being radio silent, they definitely were not; I was listening to one of the streaming scanners. There’s no way they could coordinate a response like that without radio comms. Using a police freq as a trigger would be insanely stupid, assuming the bomber didn’t want to blow himself up.

  4. Are there reports about whether SMS was working? Texts can get through when the voice equipment is overloaded. If SMS was up, then the cell system was up.

    A tweet from Mass. EMA suggested that people text instead of calling:

  5. k9zw says:

    There is an incredible amount of information being given out, retracted, recanted, denied, modified and augmented.

    So many changes that from here it is impossible to get a firm picture.

    Will return to this subject in a couple weeks.



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