Has anyone considered an em pulse from cell phone ringing nearby active recovery avionics electronics to be a risk of inadvertently triggering the ejection charges? Should cell phones be restricted from being around connected ematches, etc, during prepping as a safety precaution?
Vince Huegele
An EMP from a cell phone? Not anywhere near enough to even think about worrying about. There's a *lot* more noise from things like automobile starter motors, and the level they put out is completely negligible in this context.
triggering
This topic has been discussed from time to time, and IIRC some folks have done some testing. General consensus is that the cellphone can't produce enough EMP to fire an ematch that isn't connected to anything. What is less clear is whether or not the cellphone might affect the avionics in such a way as to cause it to fire the ematch. Even that doesn't seem likely to me. I've seen folks use walkie talkies out near the pads with rockets nearby ready to launch, and that's never caused a problem.
=E2=88=AB
At least not yet.
When I go to China Lake NWS, after they complete the live background check, they ask you to turn off all cell phones. Perhaps they have that rule from the older days of higher power analog cell phones?
Jerry
Last year I had a flight where a 300mW 2m transmitter corrupted the data on both an RDAS and AltAcc. It didn't bother the RDAS but the AltAcc acceleration measurement took a couple of large hits during flight which resulted in a deployment considerably earlier than desired.
The transmitter was located with the altimeters and was of course also very close to the e-matches. But the 300mW of output power did _not_ fire the e-matches. A cell phone may behave differently because it has higher output power and operates on a much higher frequency.
Things to do to prevent problems.
Electric field coupling is primarily a problem with an open loop. It can induce voltages on a circuit. The field difference between the two open points in the circuit causes the problem. But, this cannot typically support large currents. So with the low igniter resistance and close spacing between the open ends of the wires, you would need field strengths on the order of say, a lightning strike. But keep the open ends shorted (or at least loaded by the altimeter) and this shouldn't be a problem. Until that lightning strike anyway.
Magnetic field coupling is an issue with closed loops and induces currents in the loops. The amount of coupling is dependant on the loop area of the circuit being coupled to. For an igniter, this loop area is maximized when the connecting wires are formed into as large a loop as possible with the ends connected. A situation that almost never occurs in rockets. Minimize the loop area by twisting the igniter leads together. This creates a situation where the magnetic field produces a positive current on one twist and negative on the next. This pretty much cancels out the effect.
Electromagnetic coupling is just a variation on the above. Twisting the wire pairs minimizes this as well.
What version of coupling will be caused by any particular source? Hard to say. In the space close to a transmit antenna (with the definition of "close" being very fuzzy) either the magnetic or electric field will dominate depending on the antenna. Only after you get out of this "near field" and into the "far field" is it an electromagnetic wave. Shielded twisted pair wire is the way to go. The shield protects from electric fields and the twists protect you from magnetic fields.
When I was poking around in the comments and such for the FAA space launch rules, I noticed that the FAA has a requirement that the no fire current of igniters be 20dB above any possible EMI induced current. Electric matches are far too sensitive to qualify even though these systems are typically very well shielded. (shielded twisted pair wires, overbraid on cable assemblies, metal enclosures, metal connectors with EMI backshields, etc.)
No point in dismissing the issue. Turn off all transmitters when within 5feet of recovery electronics. Why not? Expecting a call from the stock broker? Thats what voicemail is for.
We could very well test every altimeter on the market with every possible configuration against every possible cell phone out there. Then next month, the cell companies come out with GSM4+ or some such scheme and G-WIZ comes out with another fancy altimeter and all the testing is for not.
My cell phone scrambles my monitor just before it rings. Has to be within a foot though. You don't want to be helping someone lift their rocket into position when the ebay passes by your cell phone and you set off the electronics.
Safety first, cell phones off.
RDH8
We did some test with regards to an ATV system, for our Altus 40 launch, we were running the TX right above the staging and deployment electronics. We had some concerns that things would not work as planned. Running about 10 watts PEP at UHF frequencies we did not have any problems with the FC-877 we were using (both on the ground and in actual flight). The antenna feed line ran within three inches of the FC on it way down to the antenna in the fins. Both the accelerometer and baro sensors behaved normally in post review of the data.
Different frequencies may present different problems with the same set of electronics. It would be best not to tempt fate when you don't have to... And always test, test, test
We have a dubbing facility here at work with a large "no cell phone" sign out front. Just the RF preamble to the ringing was causing noise on the audio side of things.
David Atha Aerospace VE6RKT
V> Has anyone considered an em pulse from cell phone ringing nearby active
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.