cberrya6e
Member
- Joined
- Apr 30, 2014
- Messages
- 5
- Reaction score
- 0
I am new to the Forum and have something to pass along. I had an interesting "event" several weeks ago. I was launching a brand new 4" AGM-33 Pike with redundant dual deploy electronics onboard. The altimeters used were a Transolve P6K and an Altus Metrum Telemega and ground testing had shown no issues. Pad side, with the rocket on the rail, I armed the Telemega and received the proper aural indication that continuity was good and that the altimeter recognized PAD state. Next, I armed the P6K and it beeped once or twice before stopping and I heard some sort of a hiss from within the rocket. I initiated my escape sequence and started running. Before I got more than 10' from the beast, ejection charges fired and the rocket deployed its recovery guts around the pad.
Analysis after this showed that the P6K had fired both the APOGEE and MAIN ejection charges (not the Telemega). After a series of emails with both Bdale Garbee (Altus Metrum) and John Fleischer (Transolve) and discussions with others, the initial potential culprits were identified as being the arming switch (Schurter rotary type) or interference between the 70cm band transmitter on the Telemega and the P6K. I performed some simple tests at home and could not induce any sort of a brownout/power cut using the switch; further review and discussions shows that these switches are sold and used by a number of high-profile vendors in our hobby and I felt that this was not the real problem. Furthermore, I realized that my ground testing prior to the launch attempt was always with the ebay in the horizontal position. In this state, the Telemega is in an IDLE state and is in a receive mode awaiting comms from a ground station. Once it is in the PAD mod (vertical), the altimeter goes into full transmit and does not receive inbound comms. Using LEDs in the ejection charge connectors, I was able to repeat 100% the results that the launch attempt revealed - once the Telemega and the P6K were both on and booted, the P6K would fire both LEDs. The start sequence did not affect the outcome - the results were identical regardless of which device was started first.
To fully close the loop on this, I took my ebay to a lab at Rice University and ran some tests there. By connecting oscilloscope leads to the P6K ejection charge outputs across a 1 ohm resistor and using a spectrum analyzer targeting the 435 Mhz band, we were able to conclusively show that the P6K does not filter out the RF from the Telemega and the current induced by this energy is enough to cause the P6K to "see" flight conditions that lead to triggering of the ejection charges. Here is a screenshot of the scope for one of the tests:
View attachment 173794
I forwarded these results to John Fleischer and after some discussion we both agreed that this was a problem and that the Telemega and the P6K should not be situated in the same ebay.
I like the simplicity and the robustness of the P6K. But I am new to the telemetered side of the hobby and this was a bit of a shock for me. Given that the Telemega is relatively new, I thought I would post this to alert others to this issue. I will continue to use my P6Ks, but not on any of my radio birds without having the two altimeters separated within the rocket body.
Regards,
Chuck Berry
Houston, TX
TRA L2 #14528
Analysis after this showed that the P6K had fired both the APOGEE and MAIN ejection charges (not the Telemega). After a series of emails with both Bdale Garbee (Altus Metrum) and John Fleischer (Transolve) and discussions with others, the initial potential culprits were identified as being the arming switch (Schurter rotary type) or interference between the 70cm band transmitter on the Telemega and the P6K. I performed some simple tests at home and could not induce any sort of a brownout/power cut using the switch; further review and discussions shows that these switches are sold and used by a number of high-profile vendors in our hobby and I felt that this was not the real problem. Furthermore, I realized that my ground testing prior to the launch attempt was always with the ebay in the horizontal position. In this state, the Telemega is in an IDLE state and is in a receive mode awaiting comms from a ground station. Once it is in the PAD mod (vertical), the altimeter goes into full transmit and does not receive inbound comms. Using LEDs in the ejection charge connectors, I was able to repeat 100% the results that the launch attempt revealed - once the Telemega and the P6K were both on and booted, the P6K would fire both LEDs. The start sequence did not affect the outcome - the results were identical regardless of which device was started first.
To fully close the loop on this, I took my ebay to a lab at Rice University and ran some tests there. By connecting oscilloscope leads to the P6K ejection charge outputs across a 1 ohm resistor and using a spectrum analyzer targeting the 435 Mhz band, we were able to conclusively show that the P6K does not filter out the RF from the Telemega and the current induced by this energy is enough to cause the P6K to "see" flight conditions that lead to triggering of the ejection charges. Here is a screenshot of the scope for one of the tests:
View attachment 173794
I forwarded these results to John Fleischer and after some discussion we both agreed that this was a problem and that the Telemega and the P6K should not be situated in the same ebay.
I like the simplicity and the robustness of the P6K. But I am new to the telemetered side of the hobby and this was a bit of a shock for me. Given that the Telemega is relatively new, I thought I would post this to alert others to this issue. I will continue to use my P6Ks, but not on any of my radio birds without having the two altimeters separated within the rocket body.
Regards,
Chuck Berry
Houston, TX
TRA L2 #14528