A few antenna / magnetic / carbon / RF / battery questions

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stealth6

stealth6

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So, a couple questions regarding RF/electrical interference. I'm designing a rocket with some pretty tight quarters, and wondering about a couple of potential issues. I know that carbon fiber blocks RF signals and so it's not a good idea to encase trackers and such (at least the antennas) inside carbon airframes. But.....

* I've got a 7 inch antenna (TeleMini V1) that's going up inside a fiberglass nosecone. However, the altimeter itself and about the first 3/4" or so of the antenna will be inside the airframe, which will be carbon fiber. Will having that short section of antenna "inside" the airframe be a problem do you think? Anyone run something similar, and if so, did it work or was it a problem?

* I'm also utilizing a Featherweight magnetic switch. It will be located adjacent to (and quite close to) the antenna. Will this be a problem? Any interference issues?

* The LiPo battery (110mAh, 3.7v) will also be located very close to the antenna - again, should I be concerned about this?

OK, technically that's five questions, not "a couple", I know. But regardless, any answers/advice are appreciated.
Thanks,
s6
 
No answers, but a question: you only need the tracker after the rocket is down. Will the NC shoulder still be in the airframe after deployment?
 
Hmmm. The answer is - "sort of". About 3 inches of the carbon airframe (including that bit that overlaps 3/4" of the antenna) will basically stay attached to what is normally the nosecone shoulder. It's not a standard design (but not terribly different either).

s6
 
As long as the antenna is inside the glass I think you will be ok.

Any interference issues are best tested with the real gear in proximity to each other.

Battery is not an issue.
 
I do fully plan to ground test, and test, and test this setup before I push any launch buttons, of course. Just trying to see if there are any obvious no-no's, or even if anyone else has done this with no problems, before I get too far down the path.

s6
 
You should test it, but personally I would move the antenna. CF shields electromagnetic signals. Good chance you will change the effective antenna length having it sit inside CF.

The magnetic switch/battery combo could cause a slight glitch/spike when turned on, but after that the state is constant and will cause no problems during flight.
 
stealth6 said:
I do fully plan to ground test, and test, and test this setup before I push any launch buttons, of course. Just trying to see if there are any obvious no-no's, or even if anyone else has done this with no problems, before I get too far down the path.

s6
Click to expand...

I don't have the same scenario but close. I use a TeleGPS in my glass NC and the shoulder is in the CF tube but it separates. For what it's worth I have no issues all the way up while together, but I would echo what others have said and ground est ground test ground test. Then start with a couple of low flights. I used a low alt same motor to do two 3-4000 foot flights to shake out the tracking and recovering system, and that was after a bunch of ground testing.
 
stealth6 said:
So, a couple questions regarding RF/electrical interference. I'm designing a rocket with some pretty tight quarters, and wondering about a couple of potential issues. I know that carbon fiber blocks RF signals and so it's not a good idea to encase trackers and such (at least the antennas) inside carbon airframes. But.....

* I've got a 7 inch antenna (TeleMini V1) that's going up inside a fiberglass nosecone. However, the altimeter itself and about the first 3/4" or so of the antenna will be inside the airframe, which will be carbon fiber. Will having that short section of antenna "inside" the airframe be a problem do you think? Anyone run something similar, and if so, did it work or was it a problem?

Answer: Most likely not a problem. Do a ground range check and you will likely notice good range.

* I'm also utilizing a Featherweight magnetic switch. It will be located adjacent to (and quite close to) the antenna. Will this be a problem? Any interference issues?

Answer: The rule of thumb is to try to keep your antenna in free space. Any metal paralleling the antenna could attenuate and cut down on your range. Whether or not the stray Rf will mess with your switch, I'd set everything up with bare charges and ground test it in ready to launch mode for 30 to 60 minutes. You could ask Adrian if Rf messes with the switch. If your switch is at the base of the antenna, It won't affect with your range.


* The LiPo battery (110mAh, 3.7v) will also be located very close to the antenna - again, should I be concerned about this?

Answer: Same thing as the answer above. If it's on the opposite side of the board paralleling the tele-mini, it shouldn't be a problem. If it's paralleling the antenna wire, you could have range attenuation

OK, technically that's five questions, not "a couple", I know. But regardless, any answers/advice are appreciated.
Thanks,
s6
Click to expand...

Answers were placed inline above. Kurt Savegnago
 
Bat-mite said:
No answers, but a question: you only need the tracker after the rocket is down. Will the NC shoulder still be in the airframe after deployment?
Click to expand...

Wrong, you need the tracker functioning "in air" so one can get a good bearing if doing RDF because one may lose the signal once the rocket is down. If using a GPS tracker, one wants good clean position packets as close to the touchdown that they can get. With RDF, if one loses their bearing, they may be screwed if they can't get close enough to pick up a new signal. GPS will give one a place on a map and most likely when they get within range, if they can't see the rocket, they'll be close enough to get a new position packet for the final resting place. No muss, no fuss, no attenuators, no guessing the range.

Now a little strategy for RDF that could be very helpful is some handheld GPS units like Garmin have a "Sight 'n Go" feature. One sights between marks on the GPS and they can lock a datum in the unit and follow a bearing line
to where they sighted. I found this useful for visual recoveries or rockets landing quite a distance away but you can "just see it". In some recoveries, I had to walk around obstructions and it gave me an accurate line. I once sighted a downed rocket over a drainage ditch I couldn't immediately cross over. I shot the line and walked a quarter of a mile away from the rocket crossed over, followed the line on the Vista HcX and it got me back to the rocket.

I think one could hold the GPS parallel to their RDF Yagi and shoot a bearing line towards the strongest signal. Might help in getting one close so they could pick up the signal again if the rocket goes out of range.

Kurt Savegnago
 
ksaves2 said:
Wrong, you need the tracker functioning "in air" so one can get a good bearing if doing RDF because one may lose the signal once the rocket is down. If using a GPS tracker, one wants good clean position packets as close to the touchdown that they can get. With RDF, if one loses their bearing, they may be screwed if they can't get close enough to pick up a new signal. GPS will give one a place on a map and most likely when they get within range, if they can't see the rocket, they'll be close enough to get a new position packet for the final resting place. No muss, no fuss, no attenuators, no guessing the range.
Click to expand...

Guess I never thought of that. I haven't yet launched a rocket out of sight, but I expect to within the next few months. Thanks for the tip.
 
Bat-mite said:
Guess I never thought of that. I haven't yet launched a rocket out of sight, but I expect to within the next few months. Thanks for the tip.
Click to expand...


Nooooooooo problem.:) Bottom line is you want the tracker to function throughout the entire flight. It's especially important for RDF because one is hunting the bearing throughout the course of the flight. I've seen winds aloft do screwy things to out of sight rockets while GPS tracking. Like the rocket drifting 180 degrees from the ground wind direction. If one doesn't keep that in mind, they might not swing their antenna around to get the bearing while doing RDF. If one can't see the rocket or the events, if they don't get a bearing before the rocket lands, they might be out of luck and have no idea where to even begin the search to reacquire the signal. This is one of the reasons I'm a big fan of GPS tracking both APRS, a' la GPS Altus Metrum and Eggfinder/TRS flavors. You know the altitude from where the last position packet was transmitted and can tell the direction of travel of the rocket very easily.

One nifty thing about Altus Metrum GPS tracking is one can use their receiving equipment to get a lot of data via real time AND/OR their GPS devices ALSO transmit APRS packets at the same time so one can use ham radio APRS receivers to go portable
after the flight is down. I didn't realize this until I got their B/T receiver and setup a Tele-GPS to send an APRS packet. I thought it was either/or but it's not. It's both at the same time. Talk about utility. If their receiver could be selected to decode APRS man the ham radio APRS fliers would buy a bunch of the Tele-BT units for their Beeline 70cm APRS trackers. Kurt Savegnago
 
One thing that might be a problem. There could be a slight possibility of the radio equipment causing false switching of the magnetically activated switch. I would keep it as far away as possible from any radio transmitter.
 
I ran into an issue with RF inhibiting GPS lock with the Telemetrum in my current av-bay. Lock time was improved by adding an RF choke to the allthread. Best I can figure, the allthread was acting as an antenna near the harmonic of the GPS receiver; adding the the choke de-tuned it so that I could quickly acquire lock.

I mention it because I found this during ground testing... if you run into a similar problem, it may be something for you to consider.


Later!

--Coop
 
How'd you add a choke to the all-thread for the less electronically inclined? Weird things can happen with Rf.
I had metallic paint attenuate a 70cm Beeline GPS signal yet the GPS receiver held lock on 7 to 10 satellites the
entire time. Rocket came down within sight and the .kml file recorded to memory showed the flightpath.

Kurt Savegnago


Coop said:
I ran into an issue with RF inhibiting GPS lock with the Telemetrum in my current av-bay. Lock time was improved by adding an RF choke to the allthread. Best I can figure, the allthread was acting as an antenna near the harmonic of the GPS receiver; adding the the choke de-tuned it so that I could quickly acquire lock.
I mention it because I found this during ground testing... if you run into a similar problem, it may be something for you to consider.


Later!

--Coop
Click to expand...
 

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