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Carbon Fiber and GPS transparency but interstage is fiberglass

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ColumbiaNX01

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I just thought I would ask. Sounds like a dumb question but here ya go.

Yes, Carbon Fiber blocks GPS signal. In the old days people would not use a switch for their altimeters they would just twist and tape the wires outside the vent hole. So that being said a GPS that has a wire whip antenna, can that stick out of a vent hole and then be taped to the outside of the rocket on switch band? I know this is asking something from way out of left field. Yes, in a perfect world it should stay inside.

My 2 stage is all carbon except the interstage coupler. When rocket is on pad put together all there is is carbon. Once it stages the fiberglass of the interstage coupler will be shown exposed.

I cannot put GPS anywhere else but in the interstage coupler. This is the GPS for booster. As for the GPS for sustainer it is in fiberglass nose cone so that is okay. Next build I will not be using carbon is certain areas to fix this situation, but now I am stuck trying to find a solution lol.

Here is a link to my project.

https://www.rocketryforum.com/showthread.php?137537-Black-rock-project-2-stage-2018-min-diameter

andrew
 

dhbarr

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What trackers are you using, and what range do you currently get as-is?
 

OverTheTop

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When you say the GPS has a wire whip antenna, I assume you are meaning for the telemetry transmission, not for the GPS position reception? What frequency you transmitting on?

You could mount an antenna outside the airframe. It would be quite directional, depending on which way the rocket is facing, unless you do a multiple antenna installation to have all sides relatively well covered. I have read of such things (basically flat patch antennas), but my engineering expertise doesn't go that far into RF.

Maybe there are some clever RF engineers out there that can chime in for you about now :)

I would be more concerned about GPS reception, as the signal levels the receivers are working on are quite minscule (below -160dBm IIRC). The stronger the signals, the quicker the lock after loss of lock.
 

markkoelsch

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The wire whip is for transmitting the gps to your receiver. It is not the GPS receiver.
 

ColumbiaNX01

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When you say the GPS has a wire whip antenna, I assume you are meaning for the telemetry transmission, not for the GPS position reception? What frequency you transmitting on?

You could mount an antenna outside the airframe. It would be quite directional, depending on which way the rocket is facing, unless you do a multiple antenna installation to have all sides relatively well covered. I have read of such things (basically flat patch antennas), but my engineering expertise doesn't go that far into RF.

Maybe there are some clever RF engineers out there that can chime in for you about now :)

I would be more concerned about GPS reception, as the signal levels the receivers are working on are quite minscule (below -160dBm IIRC). The stronger the signals, the quicker the lock after loss of lock.
Yes, Antenna for the telemetry so the receiver can get location.
 

cerving

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With a RF-GPS transmitter, you have two radio systems in play... the 1.575 GHz GPS system and the radio system than sends the data to you (usually 900 MHz or 433 MHz/70 cm). You have to get both of those signals through the CF in order to get a good GPS fix and telemetry. Jim Jarvis' slot/waveguide method will work fine for the telemetry radio side (assuming you have the room to cut the proper length slot), but the GPS signal is another matter. It needs to have a clear view of the entire sky, so it's going to be difficult to do that with pure CF. If you're thinking of putting your GPS-radio tracker in the AV bay, you might want to think about using a FG coupler and switch band, and align the GPS module's antenna with the switch band.
 

blackjack2564

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It needs to have a clear view of the entire sky, so it's going to be difficult to do that with pure CF. If you're thinking of putting your GPS-radio tracker in the AV bay, you might want to think about using a FG coupler and switch band, and align the GPS module's antenna with the switch band.

Wat we do...+1 double wall coupler!
 

ksaves2

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So cut a window to fit the GPS antenna underneath to allow the satellites Rf to permeate the electronics bay and shove a fiberglass coupler down to "seal" the window. Good deal. The slot thing is a nice alternative. Kurt
 

ColumbiaNX01

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So cut a window to fit the GPS antenna underneath to allow the satellites Rf to permeate the electronics bay and shove a fiberglass coupler down to "seal" the window. Good deal. The slot thing is a nice alternative. Kurt
That is an excellent idea!!!
 

Nytrunner

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How did u come to that number?
Divide by the speed of light.

Cerving said GPS operated at ~1.5 GHz, so the corresponding wavelength for that is ~20 cm. (Unless I'm using the wrong calculation)

I recall Jim J sized his slot waveguides based on the wavelength of his telemetry, and was wondering how large a GPS waveguide would need to be.

Rf experts, please straighten out any wrinkles in my thinking.
 

plugger

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My 2 stage is all carbon except the interstage coupler. When rocket is on pad put together all there is is carbon. Once it stages the fiberglass of the interstage coupler will be shown exposed.

I cannot put GPS anywhere else but in the interstage coupler. This is the GPS for booster. As for the GPS for sustainer it is in fiberglass nose cone so that is okay. Next build I will not be using carbon is certain areas to fix this situation, but now I am stuck trying to find a solution lol.
Given you're discussing GPS in the ISC and therefore not looking to use that GPS for any type of altitude record I'd go as far as to say it doesn't matter. I say this as you're only using GPS for tracking recovery location of the booster, not for any type of altitude record recording purposes. Given that you don't need GPS lock or telemetry at apogee, all you need is GPS lock during descent to provide you with the landed location of your booster. As the GPS patch antenna and wire whip antenna will be clear from a CF perspective once you stage this should be a non-issue.
 

ksaves2

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Given you're discussing GPS in the ISC and therefore not looking to use that GPS for any type of altitude record I'd go as far as to say it doesn't matter. I say this as you're only using GPS for tracking recovery location of the booster, not for any type of altitude record recording purposes. Given that you don't need GPS lock or telemetry at apogee, all you need is GPS lock during descent to provide you with the landed location of your booster. As the GPS patch antenna and wire whip antenna will be clear from a CF perspective once you stage this should be a non-issue.
If just using for tracking, "harden" the tracker, stick it in a case and tack it on the apogee harness. Let the tracker sit out and get a lock before stuffing it inside the CF sustainer. If a really screaming high shot say 10k or above, the tracker will have plenty of time to re-establish a lock on the way down under drogue. Pop the main at 1000' or above (if the venue and wind allows) and you'll have plenty of time to get positions before touchdown. Only disadvantage is if the tracker isn't ejected and the flight is ballistic then no chance to get a position on the terminal descent to make it easier to find the pieces.

Of course if one wants a GPS altitude reading close to apogee, would need "Rf transparency" for that and if going record hunting would have to adhere to the approved GPS tracker list for that purpose. If not hunting records, can plop a Ublox chipset with a
3DR radio and will have the reliability of altitude that the Ublox is known for, for one's personal satisfaction. Kurt
 

cerving

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Divide by the speed of light.

Cerving said GPS operated at ~1.5 GHz, so the corresponding wavelength for that is ~20 cm. (Unless I'm using the wrong calculation)

I recall Jim J sized his slot waveguides based on the wavelength of his telemetry, and was wondering how large a GPS waveguide would need to be.

Rf experts, please straighten out any wrinkles in my thinking.
It would actually be about 9.5 cm, the slot is half-wavelength. A slot waveguide would actually be a bad choice for GPS, it only has one polarization so your signal reception would be highly dependent on the position of the rocket. Patch antennas are circularly polarized, so they get equal signal reception at any position; that's why they're almost universally used for GPS's. It would work just fine for the telemetry side, though.
 
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UhClem

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A slot waveguide would actually be a bad choice for GPS, it only has one polarization so your signal reception would be highly dependent on the position of the rocket. Patch antennas are circularly polarized, so they get equal signal reception at any position; that's why they're almost universally used for GPS's.
If you attempt to receive a circularly polarized signal with a linear polarized antenna you will have a fixed 3dB polarization loss. GPS satellites transmit using right hand circular polarization so will work best with that type of receiving antenna. Note that a left hand circular polarization antenna would have very high attenuation.
 

ColumbiaNX01

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Guys,

What about a simple radio tracker like a Walston. Can that transmitter be attached to the shock cord and once the event happens and the transmitter is out in the open then the receiver handled will be able to pin point the location??
 

plugger

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Guys,

What about a simple radio tracker like a Walston. Can that transmitter be attached to the shock cord and once the event happens and the transmitter is out in the open then the receiver handled will be able to pin point the location??
In short, yes. The RF part of the equation is roughly identical whether you leverage a simple tracker transmitter or a GPS tracker transmitter. That said with a simple tracker you won't be able to pinpoint location, you'll only know the rough bearing to follow to find the transmitter.
 

ColumbiaNX01

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In short, yes. The RF part of the equation is roughly identical whether you leverage a simple tracker transmitter or a GPS tracker transmitter. That said with a simple tracker you won't be able to pinpoint location, you'll only know the rough bearing to follow to find the transmitter.
I have never used a RF tracker. But I figure you follow the beeps. Where the beeps get stronger thats the direction of the rocket. But with putting it on the shock cord unlike trying to get a lock with gps when the rocket is up there and moving fast but once the RF transmitter is out and exposed on the shock cord you can get an easy lock with the RDF?
 

plugger

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I have never used a RF tracker. But I figure you follow the beeps. Where the beeps get stronger thats the direction of the rocket. But with putting it on the shock cord unlike trying to get a lock with gps when the rocket is up there and moving fast but once the RF transmitter is out and exposed on the shock cord you can get an easy lock with the RDF?
Personally I think you should probably consider doing a couple transmitter test flights if you're going to use a simple transmitter instead of GPS. Either that or offload tracking to someone at the launch who's experienced in that sort of thing. It's not just a follow the beeps proposition, you'll need a directional antenna and follow the bearing by signal strength which requires a handheld radio that displays that information. It's a combination of science, skill, and experience. I wouldn't want to have my first experience with this sort of system on a two stage min diameter stack flight; you'll already have more than enough on your plate to worry about without stressing about directional finding your booster.

If you're looking for simplicity I'd highly recommend choosing GPS over a standard RDF transmitter.
 

ColumbiaNX01

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Personally I think you should probably consider doing a couple transmitter test flights if you're going to use a simple transmitter instead of GPS. Either that or offload tracking to someone at the launch who's experienced in that sort of thing. It's not just a follow the beeps proposition, you'll need a directional antenna and follow the bearing by signal strength which requires a handheld radio that displays that information. It's a combination of science, skill, and experience. I wouldn't want to have my first experience with this sort of system on a two stage min diameter stack flight; you'll already have more than enough on your plate to worry about without stressing about directional finding your booster.

If you're looking for simplicity I'd highly recommend choosing GPS over a standard RDF transmitter.
Of course. My high altitude flight is next year. In the mean time I will be testing in lower altitude flights once I decide on which fr tracker. If you have been following along in the thread my rocket it fiberglass and the airframe is carbon. I would not be able to get a lock with the gps. Yes, I would rather have a gps but for this rocket that is not gonna happen. But big picture just thinking about tracking and things its nice to have 2 separate tracker systems; a gps and fr tracker.

Next year my anticipated altitude in the 2 stage is around 10k for the booster and that is where the rf tracker will be. and the sustianer gps will be in nose cone.
 

blackjack2564

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Often overlooked, your last packet with GPS can be several hundred feet/yards from actual landing location.
Having Rf on board makes that last bit of tracking so much easier if caught in brush, tall grass, crops, trees etc. where you can't see the landing zone clearly.

Of course some GPS units can double as RF's with right ground radio.
 

ksaves2

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Often overlooked, your last packet with GPS can be several hundred feet/yards from actual landing location.
Having Rf on board makes that last bit of tracking so much easier if caught in brush, tall grass, crops, trees etc. where you can't see the landing zone clearly.

Of course some GPS units can double as RF's with right ground radio.
ie: Yagi antenna with an attenuator for RDF but if you're trying to RDF a GPS tracker, one will likely pick up a "final resting" place position as long as the GPS has a lock. Some APRS GPS trackers stop transmitting without a lock so beware of one's hardware.
If there is an "RDF" mode for the APRS/GPS tracker that would be a nice failsafe situation. Jim also has mentioned in prior posts that a noisemaker or "screamer" on the harness helps to home in. Stupidhead here just about lost a rocket with
a strong signal coming in on the EggFinder until Stupidhead here realized I needed to zoom the map in to separate "me" from the rocket. Kurt
 

phyzzld

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If you're thinking of putting your GPS-radio tracker in the AV bay, you might want to think about using a FG coupler and switch band, and align the GPS module's antenna with the switch band.
Is there a minimum size for the FG switch band to make sure the RF penetrates the AV bay of a 4" rocket? Can this be used for both the GPS and telemetry radios? Thanks
 

Andrew_ASC

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I flew an FCC regulated TeleGPS on two flights L-1 multistage for college project this year as mechE student and rocket noob. You need to get familiar with the trackers, dude. You need to ground test a fully assembled rocket in and out. Have some friends walk off with it in many directions and practice finding it in and around trees/near buildings etc. Put it in a car if telemetry and track the route of vehicle for testing it. This will test materials for RF transparency at various ranges and angles first. You have only ten to twenty seconds of an actual flight tracking. You can't afford a screw up in flight or a lapse of how does this device function from program menu selection blah again? We found our rocket again. Another college had to use a light airplane and they failed to find a project one year, so its always cheaper and easier to learn the limits of your gear first.

Radio trackers work great for civil aircraft, ex-student pilot here... Less affected by terrain than GPS. More sensitive in signal directions as closing distance to station decreases. Okay with terrain changes, but not if station was in a mountain valley, you could lose a signal until nearly over top.
In model rockets. Radios not lose locks like GPS will under boost from high impulse motor at dozen to hundreds G loads.
GPS telemetry FCC regulated for rocket... We had discovered TeleGPS had a max tracking limit of 60.6Gs. You may discover it could do more, idk. It was rated for 8 Gs. It lost a 167G project in a desert once. It still had a lock over slight 500ft hill and into a tree line at 60G project. My humble opinion was GPS with RDF tracker dual mode took a steep learning curve to a new HAM operator. If you can select lower baud rates (FCC/Ham) high power devices, the range increases and sensitive improves as data transfer frequency, rates faster on tele. It was quite awesome as long as it was kept in limits. A radio has less limits, but like you I know very little about tracking a rocketry pure RF transmitter. We couldn't use dual RDF only mode on a UV-5R only heard the beep and no tone increased as got closer or left or right. It might need a different ham hand held radio to radio track.

Sorry for long winded rant. Felt overwhelmed too. Practice with it for a week and you'll feel better too.

In a plane the VOR radio would get more sensitive as it neared a ground station, leading to human error in missing the station, without much practice. You could overcorrect a heading to a station and miss it. I hope a rocket radio beacon doesn't behave as horridly, but expect a physical limitation of it.
 

Andrew_ASC

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You can also externally power some Yagi antennas such as a Arrow 440-5 for 70cm HAM bands to increase the reception at maximum range of receiver end for ground station as it communicates with the GPS transceiver that is transmitting data from the satellites to itself to the ground station receiver. Arrow didn't recommend holding the Yagi once you add a power source to it beyond normal rating of 10mW, so you can vehicle mount it for that kind of use. The rubber ducky antennas do not work well through vehicles or other barriers and you can get questioned about it during a HAM exam. And idk if it matters, but an electrical engineer student dork told us to make sure the GPS antenna wire was straight on transceiver to increase its reception and RF abilities.
 
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