Hi everyone,
I need to create a device for an EPIRB (Emergency Position Indicating Radio Beacon), which are used onboard various sea going vessels to signal maritime distress (for more info: http://en.wikipedia.org/wiki/Distress_radiobeacon). Once activated, the EPIRB transmits a signal via 406 MHZ to overhead satellites and aircraft. To transmit this signal when not in distress is illegal as well as a potential PITA. I work as a machinery technician for the United States Coast Guard and have an upcoming event before crab season where I will be testing EPIRB's for commercial fisherman (a fully functional test, not the self test feature they can do themselves). I have a shielded box where you place the EPIRB for testing. How it works is like this: the EPIRB's I will be testing can be manually activated with a switch or activated by going into the water. On the underside of the top of the unit there are several recessed screws. Water creates continuity between these screws and activates the unit. When we have tested them in the past, you would place the EPIRB in a bracket in a shielded box and use a stiff length of wire to create continuity between the screw heads and activate the device. then you would shut the shielded box, blocking the signal from reaching the satellite. The only access to the box is what looks like a coaxial cable connection mounted in the side where you attach the computer so that it can analyze the EPIRB's signal. EPIRB's will transmit usually every 50 seconds to one minute, theoretically allowing one to activate it and seal the box, then monitor the signal output via computer so you could deactivate it in the interval. Unfortunately, in practice, this doesn't always go so seamlessly, since some EPIRB's will transmit immediately upon activation.
To remedy this I am trying to fabricate a circuit and switch to allow a person to close or open the circuit from outside the sealed box. The EPIRB would rest in a fabricated bracket, with two stiff strands of mechanics wire making contact with the heads of the screws. A lead of some sort (maybe an alligator clip) would be attached to each length of mechanics wire; connected to each lead would be a single wire, which then would be attached to a knife switch so you could open and close the circuit. My problem is routing the wires to the exterior of the shielded box. If I just run them under the lid of the box and seal it on top of the wires, I am fairly certain the wires will be severed because of the box's design necessitates containing the EPIRB's transmission (there is a pronounced knife edge running around the interior of the lid. I am extreley hesititant try and drill the box and make some manner of shielded cable run, since the box itself is absurdly expensive and I don't want to render it incapable of containing the radio transmission. I have thought about putting a sort of timed breaker on the circuit, but that would necessitate having one timer to close the circuit and another timer several minutes later to open the circuit, giving the tester time to seal the box, test the EPIRB, then wait for the timer to break the circuit before opening the box.
I know that was all long winded and if you made it this far I appreciate your attention. If my ideas thus far are pretty crude I apologize; I am a mechanic by trade and my electrical experience usually involves boat and engine rigging (splicing and running cable, finding shorts, etc.) I would be thankful for any suggestions you guys could provide.
Best Regards
I need to create a device for an EPIRB (Emergency Position Indicating Radio Beacon), which are used onboard various sea going vessels to signal maritime distress (for more info: http://en.wikipedia.org/wiki/Distress_radiobeacon). Once activated, the EPIRB transmits a signal via 406 MHZ to overhead satellites and aircraft. To transmit this signal when not in distress is illegal as well as a potential PITA. I work as a machinery technician for the United States Coast Guard and have an upcoming event before crab season where I will be testing EPIRB's for commercial fisherman (a fully functional test, not the self test feature they can do themselves). I have a shielded box where you place the EPIRB for testing. How it works is like this: the EPIRB's I will be testing can be manually activated with a switch or activated by going into the water. On the underside of the top of the unit there are several recessed screws. Water creates continuity between these screws and activates the unit. When we have tested them in the past, you would place the EPIRB in a bracket in a shielded box and use a stiff length of wire to create continuity between the screw heads and activate the device. then you would shut the shielded box, blocking the signal from reaching the satellite. The only access to the box is what looks like a coaxial cable connection mounted in the side where you attach the computer so that it can analyze the EPIRB's signal. EPIRB's will transmit usually every 50 seconds to one minute, theoretically allowing one to activate it and seal the box, then monitor the signal output via computer so you could deactivate it in the interval. Unfortunately, in practice, this doesn't always go so seamlessly, since some EPIRB's will transmit immediately upon activation.
To remedy this I am trying to fabricate a circuit and switch to allow a person to close or open the circuit from outside the sealed box. The EPIRB would rest in a fabricated bracket, with two stiff strands of mechanics wire making contact with the heads of the screws. A lead of some sort (maybe an alligator clip) would be attached to each length of mechanics wire; connected to each lead would be a single wire, which then would be attached to a knife switch so you could open and close the circuit. My problem is routing the wires to the exterior of the shielded box. If I just run them under the lid of the box and seal it on top of the wires, I am fairly certain the wires will be severed because of the box's design necessitates containing the EPIRB's transmission (there is a pronounced knife edge running around the interior of the lid. I am extreley hesititant try and drill the box and make some manner of shielded cable run, since the box itself is absurdly expensive and I don't want to render it incapable of containing the radio transmission. I have thought about putting a sort of timed breaker on the circuit, but that would necessitate having one timer to close the circuit and another timer several minutes later to open the circuit, giving the tester time to seal the box, test the EPIRB, then wait for the timer to break the circuit before opening the box.
I know that was all long winded and if you made it this far I appreciate your attention. If my ideas thus far are pretty crude I apologize; I am a mechanic by trade and my electrical experience usually involves boat and engine rigging (splicing and running cable, finding shorts, etc.) I would be thankful for any suggestions you guys could provide.
Best Regards