Carbon everywhere
10-28-2011, 09:16 PM
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Carbon everywhere
Hello all, I have got myself into a dilemma. My new self desinged carbon canard slope soarer is mostly finished - 9 ft. wingspan - when I remembered about reciever wireshaving togo outside of any carbon fuselage, or risk losing the signal. All the electronics are mounted in both wings; the rear main wing (aileronand in flight ballast control) contains four standard size servos and the canardhouses the 2 elevater servos and the batteries.The fuselage is a carbon golfclub shaft, slightly reinforced with carbon sleeving. The only place it will fit is in the main carbonwing. One reciever wire will be fine on top of the wing but the bottom drags on the ground when landing. I have lost one of the recievers' wires before and it cost quite a bit to fix. Can I lengthen one of the wires and secure it so the extension will break and not the actuall wire or is this a bad idea?
10-29-2011, 09:30 AM
#2
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RE: Carbon everywhere
There isn't anything magic about antenna wire except it's length. You don't want to change the length. So..............
Consider how cheap it is to replace. Dirt cheap. So work on making replacing it easier. I've seen a plug-in antenna, but never researched possible plugs or their availability. If there were good, small ones, then attaching the female to the plane would work to start. Then make up a number of replacements and carry them when you go flying.
What I'd do would be to solidly attach a section at the fuselage consider everything from there out as expendable. A soldered joint in heat-shrink would give something to clamp onto. The breaks would be outboard the joint almost every time. To repair, you'd strip the heatshrink, unsolder the remainder and solder on a replacement length. Heatshink and clamp and you're ready to go again.
plug or solder, works about the same.
Consider how cheap it is to replace. Dirt cheap. So work on making replacing it easier. I've seen a plug-in antenna, but never researched possible plugs or their availability. If there were good, small ones, then attaching the female to the plane would work to start. Then make up a number of replacements and carry them when you go flying.
What I'd do would be to solidly attach a section at the fuselage consider everything from there out as expendable. A soldered joint in heat-shrink would give something to clamp onto. The breaks would be outboard the joint almost every time. To repair, you'd strip the heatshrink, unsolder the remainder and solder on a replacement length. Heatshink and clamp and you're ready to go again.
plug or solder, works about the same.
10-29-2011, 09:31 AM
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RE: Carbon everywhere
DO NOT ALTER THE LENGTH OF THE RECEIVER ANTENNA ! ! ! ! !
Receiver antennas are cut to a particular tuned length. Altering them will change the tuning and hurt your range.
I don't really have a solution for you though. Perhaps post up some pictures of what you've got so far.
Receiver antennas are cut to a particular tuned length. Altering them will change the tuning and hurt your range.
I don't really have a solution for you though. Perhaps post up some pictures of what you've got so far.
10-29-2011, 01:23 PM
#5
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RE: Carbon everywhere
Turns out my advice about the effect of partially shielding the antenna was wrong, so only one thing for it....... bad advice was removed.
10-29-2011, 01:34 PM
#6
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RE: Carbon everywhere
Two antenna make me think you have a 2.4 system. You can extend the antenna by running coax from the receiver to the unshielded antenna. This is all Spektrum does in their carbon receivers. The coax runs for several inches, then the outer shield is removed to be the antenna. Most likely it would be best to send in the receiver and have them do it for you.
10-29-2011, 02:14 PM
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RE: Carbon everywhere
It is a 2.4 system. What if I put the lower antenna into a housing that does not hide it like carbon does, like a rubber hose split down the length and glued the the underside of the wing? Maybe fiberglass, or metal, like brass or aluminum? Anything that is more transparent to the signal. And what would be the best material?
10-30-2011, 07:42 AM
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RE: Carbon everywhere
My original training was in radio and telecoms electronics. Antennas and their feed systems can do funny things.
Careful with adding coax stubs to lengthen the wire. When used like this the coax itself becomes part of the antenna system. So any extension of this sort would need to be tuned to work with the receiver. The "why" of this is that with a simple whip antenna there's no ground plane. But when you extend the whip with some coax the exterior ground braid becomes a ground plain. This can detune the exposed whip if it's not all taken into the tuning. Also until the coax itself in such a case becomes many wavelenghts long the actual extension becomes part of the tuned system as well. But done right the antennas CAN be extended in this manner. It just needs some fancy equipment to set it up so they maintain their tuned performance.
In the case of the antenna whip wires extending through a carbon skin the amount inside the skin doesn't effectively shorten it. The tuned length is still the same. But it will cut down the strength of the signal picked up by the amount of exposure reduction. But that actually isn't as bad as detuning the antenna whip by altering the length without proper tuning.
Ideally if you had been thinking ahead with all this you would have mounted the receiver out with one of the servos using an oversize simple plastic cover. The plastic cover would have been RF transparent and you would have had full exposure of the antenna whips even though they were behind a cover.
Alternately if you have flaps or similar you could have made one of the flaps out of fiberglass with no carbon and put the receiver at the rear of the wing with the antenna whips extending back into the fiberglass flap or elevon where again it would have kept the whips totally exposed.
Another option would have been to make one of the fins from simple fiberglass and epoxy and mount the receiver in the fin. Generally fins don't need the sort of stiffness and strength that you built into the wings and fuselage.
I know such things are pretty much 20-20 hindsight at this point though.
Careful with adding coax stubs to lengthen the wire. When used like this the coax itself becomes part of the antenna system. So any extension of this sort would need to be tuned to work with the receiver. The "why" of this is that with a simple whip antenna there's no ground plane. But when you extend the whip with some coax the exterior ground braid becomes a ground plain. This can detune the exposed whip if it's not all taken into the tuning. Also until the coax itself in such a case becomes many wavelenghts long the actual extension becomes part of the tuned system as well. But done right the antennas CAN be extended in this manner. It just needs some fancy equipment to set it up so they maintain their tuned performance.
In the case of the antenna whip wires extending through a carbon skin the amount inside the skin doesn't effectively shorten it. The tuned length is still the same. But it will cut down the strength of the signal picked up by the amount of exposure reduction. But that actually isn't as bad as detuning the antenna whip by altering the length without proper tuning.
Ideally if you had been thinking ahead with all this you would have mounted the receiver out with one of the servos using an oversize simple plastic cover. The plastic cover would have been RF transparent and you would have had full exposure of the antenna whips even though they were behind a cover.
Alternately if you have flaps or similar you could have made one of the flaps out of fiberglass with no carbon and put the receiver at the rear of the wing with the antenna whips extending back into the fiberglass flap or elevon where again it would have kept the whips totally exposed.
Another option would have been to make one of the fins from simple fiberglass and epoxy and mount the receiver in the fin. Generally fins don't need the sort of stiffness and strength that you built into the wings and fuselage.
I know such things are pretty much 20-20 hindsight at this point though.
10-30-2011, 10:36 AM
#11
My Feedback: (1)
RE: Carbon everywhere
Antennas and their feed systems can do funny things
The whole problem with antenna length is matching the impedance of the antenna to the receiver. Same problem with transmitters. They are not very high Q circuits because they have a fairly broad bandwidth, so there is some margin in the antenna length, though since we are at 2.4 GHz it is a small absolute length.
Most of these systems seem to be using 1/4 wave antenna in a 1/2 wave dipole, which is about 31mm in length. The one's with a single antenna must be using the ground plane of the receiver. However to calculate the length of coax would require some knowledge as to type of coax, since the speed of the signal slows down in coax depending on the materials used in it's construction and design.
10-30-2011, 10:55 AM
#12
RE: Carbon everywhere
ORIGINAL: HighPlains
Usually not so funny when you are trying to solve the problems. I worked as a design engineer on a lot of stuff over the years. Airborne military radar, communications, signal processing, instrumentation, and high power RF plasma processing systems.
The whole problem with antenna length is matching the impedance of the antenna to the receiver. Same problem with transmitters. They are not very high Q circuits because they have a fairly broad bandwidth, so there is some margin in the antenna length, though since we are at 2.4 GHz it is a small absolute length.
Most of these systems seem to be using 1/4 wave antenna in a 1/2 wave dipole, which is about 31mm in length. The one's with a single antenna must be using the ground plane of the receiver. However to calculate the length of coax would require some knowledge as to type of coax, since the speed of the signal slows down in coax depending on the materials used in it's construction and design.
Antennas and their feed systems can do funny things
The whole problem with antenna length is matching the impedance of the antenna to the receiver. Same problem with transmitters. They are not very high Q circuits because they have a fairly broad bandwidth, so there is some margin in the antenna length, though since we are at 2.4 GHz it is a small absolute length.
Most of these systems seem to be using 1/4 wave antenna in a 1/2 wave dipole, which is about 31mm in length. The one's with a single antenna must be using the ground plane of the receiver. However to calculate the length of coax would require some knowledge as to type of coax, since the speed of the signal slows down in coax depending on the materials used in it's construction and design.
10-30-2011, 11:36 AM
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RE: Carbon everywhere
Thanks for the advise, I have a plan, and tell me what you think. Next month, I will be building a floater. I will use this reciever (it is a bit large) in the floater, and I will buy a new Futaba 4 channel reciever that has a slim design which has the connections on the end instead of on top. This slim one is thin enough to fit inside the canard without making an apendage. The canard is balsa with a fiberglass cover. Will I still have to run one of the antenna wires on the bottom, (as well as on top)? Can I have both wires on top, (in different directions)?
10-30-2011, 04:44 PM
#14
RE: Carbon everywhere
Having both on the top, pointing 90 degrees from one another and both horizontal will work just fine. Just as a side note, I'm pretty sure this is common knowledge but never point your TX antenna directly at the model. The signal radiates in an inverted cone shape.
10-31-2011, 11:40 AM
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RE: Carbon everywhere
If your canard is all balsa and actual glass with no carbon skinning you don't even need to put the wires outside of the skins. Wood, glass and resin are RF transparent enough that you can have the antennas inside the skin. However with 2.4Ghz they should be placed at 90 degrees to each other unless it's one of the styles where the wires come out opposite sides. But in those cases we're talking about receivers with "slaves" where the one two part dipole wires are in line with each other but the slave dipole is at 90 degrees to the other main unit dipole. On single unit receivers where the antennas are coming out the case or off the board on adjacent sides the two wires are intended to be laid out at 90 to each other and straight out from the board they are mounted to.
Speedracertrixie, the primary pattern from a simple whip or loaded coil antenna like we have on the old 72 stuff or on the new 2.4 Ghz radios is more accurately described as a donut shape or torus with the antenna located at the center axis of the "hole". But that's the simplistic picture. In actual fact there's other sub direction spikes at all manner of angles radiating from the primary torus shaped field's "hole". And with the 2.4Ghz sets the patterns are further distorted by having the antenna hinged so it can poke upright while the case is near horizontal, the presence of a metal carry handle if one is used and even the flyer's body standing so close to the transmitter. And then if we add the ground reflections to the pattern we really do have "duck soup".
Despite that all in all I totally agree that the last thing you want is to point the Tx antenna directly at the model. Even though flyers have typically gotten away with it for years thanks to those secondary strong spikes that come out of the donut hole. And the first thing the flyer should do if they lose control and suspect a loss of signal is hold the Tx as high above their head as they can with the antenna pointed straight up in the hopes that the primary "donut" pattern direction will be strong enough to restore control enough to bring 'er home..... and then don't do that again....
Highplains, from your last post I suspect you've done some time working and learning RF systems as well.... I always found that with the oddball RF antenna stuff it really helped if I wore a tall conical hat with stars and moons on it ahd a long flowing cape. And my primary adjustment tool looked suspiciously like a wizard's wand....
Speedracertrixie, the primary pattern from a simple whip or loaded coil antenna like we have on the old 72 stuff or on the new 2.4 Ghz radios is more accurately described as a donut shape or torus with the antenna located at the center axis of the "hole". But that's the simplistic picture. In actual fact there's other sub direction spikes at all manner of angles radiating from the primary torus shaped field's "hole". And with the 2.4Ghz sets the patterns are further distorted by having the antenna hinged so it can poke upright while the case is near horizontal, the presence of a metal carry handle if one is used and even the flyer's body standing so close to the transmitter. And then if we add the ground reflections to the pattern we really do have "duck soup".
Despite that all in all I totally agree that the last thing you want is to point the Tx antenna directly at the model. Even though flyers have typically gotten away with it for years thanks to those secondary strong spikes that come out of the donut hole. And the first thing the flyer should do if they lose control and suspect a loss of signal is hold the Tx as high above their head as they can with the antenna pointed straight up in the hopes that the primary "donut" pattern direction will be strong enough to restore control enough to bring 'er home..... and then don't do that again....
Highplains, from your last post I suspect you've done some time working and learning RF systems as well....
I always found that with the oddball RF antenna stuff it really helped if I wore a tall conical hat with stars and moons on it ahd a long flowing cape. And my primary adjustment tool looked suspiciously like a wizard's wand....
