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Help with Student Project.
I've voulenteered to help the SDSU mechanical engineering studens get
telemetry from their rocket see: http://www-rohan.sdsu.edu/~sharring/sdsurocket.html. I have all the electronics working, I'm using a commercial 910Mhz telemetry radio, I have every thing working except the antenna. For the last launch I burred a dipole in the plywood fin, alas the rocket did not launch it caught fire and burned up the fins. (It did not burn as far as the electronics.) The new fins are carbon fiber composite so no antenna there... The rocket will get to mach 2 so small wires sticking out will probably break or burn up. I have enough power and ground side gain that I need no gain from the rocket, an isotropic radiator with 3db of loss would be fine. Any suggestions? My ideas and thoughts: 1)Simple 1/4 wave vertical sticking out the bottom plate of the rocket near the engine. Pros: simple. Cons: lots of metal to block the signal and mess up the pattern. Not clear if the ionized exhaust will block the signal. Antenna pattern is almost exactly wrong. (Telemetry really needed for recovery tracking so ionization fading is not a deal killer) 2)Horizontal dipole at the bottom plate of engine. All the problems of #1 except pattern. 3)Put Fiberglass windows in the electronics bay near the nose of the rocket. One window on each side, Driving two hosrizontal dipoles with a power splitter, one dipole on each side. Pros: Easy to do. Cons: I don't know what the pattern would be like, or exactly how I shoudl phase the two antennas on opposite sides. (Some metal between then so not a clean situation.) Resources: It have a minicircuits SMA 2 way power splitter, and can make precise metal parts (0.002" or better). I do not have any antenna testing equipment that is any good at 900Mhz. so any suggestions... Paul (Kl7JG) |
Wonder if the rocket body is tall enough to tape thin wires
to the sides for a dipole, or 1/4 wave... IE: a dipole for 910 mhz would be about 6.1 inches or so...3.05 inches per leg of the dipole, if center fed...Seems you could wrap the thin 3 inch legs around the rocket body, and make a "circle" dipole of sorts...You could stagger the ends, so they aren't close together, or you could even run it vertical...Magnet wire would be ok, if you could get some strong tape, glue, epoxy, silicone, etc, to stick it to the body...The "bump" on the body wouldn't be that drastic I don't think, but you'd have to talk to your rocket guys about that....MK |
Good Lord, forget the power splitter and all the rest of that stuff. Find a
place on the rocket that you can have a simple copper foil dipole fed with a coax "split tube balun". You need more info on how to do that? Just post here and I'll do what I can. Jim Weir SDSU Class of '67 |
Your question is interesting, mach II, wow!
I found this page, it deals with models constructed of carbon fiber--and their worries about it affecting antenna/signals: http://www.rcuniverse.com/forum/carb...2747045/tm.htm A guy or two there have claimed to have done some tests, how relevant these are to you, you will have to discern.... If their claims are correct, and operation of an antenna around, under or near carbon fiber is possible--how about copper foil tape on the fins--under a gelcoat??? Just an idea.... Warmest regards, John wrote in message ... | I've voulenteered to help the SDSU mechanical engineering studens get | telemetry from their rocket see: | http://www-rohan.sdsu.edu/~sharring/sdsurocket.html. | | I have all the electronics working, I'm using a commercial 910Mhz | telemetry radio, I have every thing working except the antenna. | | For the last launch I burred a dipole in the plywood fin, alas | the rocket did not launch it caught fire and burned up the fins. | (It did not burn as far as the electronics.) | | The new fins are carbon fiber composite so no antenna there... | | The rocket will get to mach 2 so small wires sticking out will | probably break or burn up. | | | I have enough power and ground side gain that I need no gain | from the rocket, an isotropic radiator with 3db of loss would be fine. | | | Any suggestions? | | | My ideas and thoughts: | | 1)Simple 1/4 wave vertical sticking out the bottom plate of the rocket | near the engine. | | Pros: | simple. | Cons: | lots of metal to block the signal and mess up the pattern. | Not clear if the ionized exhaust will block the signal. | Antenna pattern is almost exactly wrong. | | (Telemetry really needed for recovery tracking so ionization fading is | not a deal killer) | | | 2)Horizontal dipole at the bottom plate of engine. | All the problems of #1 except pattern. | | | | | 3)Put Fiberglass windows in the electronics bay near the nose of the | rocket. One window on each side, Driving two hosrizontal dipoles with | a power splitter, one dipole on each side. | | Pros: Easy to do. | Cons: | I don't know what the pattern would be like, or exactly how I shoudl | phase the two antennas on opposite sides. (Some metal between then so | not a clean situation.) | | Resources: | It have a minicircuits SMA 2 way power splitter, and can make precise | metal parts (0.002" or better). | I do not have any antenna testing equipment that is any good at | 900Mhz. | so any suggestions... | | | Paul (Kl7JG) | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
I'm surpised no one has asked how much transmit power is available, and how
high the rocket is expected to fly. Regardless, unless a micropower transmitter is being used, it seems to me that a very simple quarter wave nose tip made if 1/8" rod or similar material would only protrude a few inches above the nose and would probably do the job. At this frequency, even a tiny metal mass inside the nose would probably be a sufficiently good counterpoise for feeding it. This seems like a simple problem (or 'no problem'). I'm surprised at the complex solutions. Joe W3JDR wrote in message ... I've voulenteered to help the SDSU mechanical engineering studens get telemetry from their rocket see: http://www-rohan.sdsu.edu/~sharring/sdsurocket.html. I have all the electronics working, I'm using a commercial 910Mhz telemetry radio, I have every thing working except the antenna. For the last launch I burred a dipole in the plywood fin, alas the rocket did not launch it caught fire and burned up the fins. (It did not burn as far as the electronics.) The new fins are carbon fiber composite so no antenna there... The rocket will get to mach 2 so small wires sticking out will probably break or burn up. I have enough power and ground side gain that I need no gain from the rocket, an isotropic radiator with 3db of loss would be fine. Any suggestions? My ideas and thoughts: 1)Simple 1/4 wave vertical sticking out the bottom plate of the rocket near the engine. Pros: simple. Cons: lots of metal to block the signal and mess up the pattern. Not clear if the ionized exhaust will block the signal. Antenna pattern is almost exactly wrong. (Telemetry really needed for recovery tracking so ionization fading is not a deal killer) 2)Horizontal dipole at the bottom plate of engine. All the problems of #1 except pattern. 3)Put Fiberglass windows in the electronics bay near the nose of the rocket. One window on each side, Driving two hosrizontal dipoles with a power splitter, one dipole on each side. Pros: Easy to do. Cons: I don't know what the pattern would be like, or exactly how I shoudl phase the two antennas on opposite sides. (Some metal between then so not a clean situation.) Resources: It have a minicircuits SMA 2 way power splitter, and can make precise metal parts (0.002" or better). I do not have any antenna testing equipment that is any good at 900Mhz. so any suggestions... Paul (Kl7JG) |
You might take a look at slot antennas.
wrote in message ... I've voulenteered to help the SDSU mechanical engineering studens get telemetry from their rocket see: http://www-rohan.sdsu.edu/~sharring/sdsurocket.html. I have all the electronics working, I'm using a commercial 910Mhz telemetry radio, I have every thing working except the antenna. For the last launch I burred a dipole in the plywood fin, alas the rocket did not launch it caught fire and burned up the fins. (It did not burn as far as the electronics.) The new fins are carbon fiber composite so no antenna there... The rocket will get to mach 2 so small wires sticking out will probably break or burn up. I have enough power and ground side gain that I need no gain from the rocket, an isotropic radiator with 3db of loss would be fine. Any suggestions? My ideas and thoughts: 1)Simple 1/4 wave vertical sticking out the bottom plate of the rocket near the engine. Pros: simple. Cons: lots of metal to block the signal and mess up the pattern. Not clear if the ionized exhaust will block the signal. Antenna pattern is almost exactly wrong. (Telemetry really needed for recovery tracking so ionization fading is not a deal killer) 2)Horizontal dipole at the bottom plate of engine. All the problems of #1 except pattern. 3)Put Fiberglass windows in the electronics bay near the nose of the rocket. One window on each side, Driving two hosrizontal dipoles with a power splitter, one dipole on each side. Pros: Easy to do. Cons: I don't know what the pattern would be like, or exactly how I shoudl phase the two antennas on opposite sides. (Some metal between then so not a clean situation.) Resources: It have a minicircuits SMA 2 way power splitter, and can make precise metal parts (0.002" or better). I do not have any antenna testing equipment that is any good at 900Mhz. so any suggestions... Paul (Kl7JG) |
nah, he needs a fractal patch or two.
"Fred W4JLE" wrote in message ... You might take a look at slot antennas. wrote in message ... I've voulenteered to help the SDSU mechanical engineering studens get telemetry from their rocket see: http://www-rohan.sdsu.edu/~sharring/sdsurocket.html. I have all the electronics working, I'm using a commercial 910Mhz telemetry radio, I have every thing working except the antenna. For the last launch I burred a dipole in the plywood fin, alas the rocket did not launch it caught fire and burned up the fins. (It did not burn as far as the electronics.) The new fins are carbon fiber composite so no antenna there... The rocket will get to mach 2 so small wires sticking out will probably break or burn up. I have enough power and ground side gain that I need no gain from the rocket, an isotropic radiator with 3db of loss would be fine. Any suggestions? My ideas and thoughts: 1)Simple 1/4 wave vertical sticking out the bottom plate of the rocket near the engine. Pros: simple. Cons: lots of metal to block the signal and mess up the pattern. Not clear if the ionized exhaust will block the signal. Antenna pattern is almost exactly wrong. (Telemetry really needed for recovery tracking so ionization fading is not a deal killer) 2)Horizontal dipole at the bottom plate of engine. All the problems of #1 except pattern. 3)Put Fiberglass windows in the electronics bay near the nose of the rocket. One window on each side, Driving two hosrizontal dipoles with a power splitter, one dipole on each side. Pros: Easy to do. Cons: I don't know what the pattern would be like, or exactly how I shoudl phase the two antennas on opposite sides. (Some metal between then so not a clean situation.) Resources: It have a minicircuits SMA 2 way power splitter, and can make precise metal parts (0.002" or better). I do not have any antenna testing equipment that is any good at 900Mhz. so any suggestions... Paul (Kl7JG) |
Doesn't his original post "indicate" he wishes a "horizontal" polarized ant,
as opposed to vertical nose rod? At least, that is why I dismissed the "obivious." Warmest regards, John "W3JDR" wrote in message news:1cIee.3075$fQ2.31@trnddc05... | I'm surpised no one has asked how much transmit power is available, and how | high the rocket is expected to fly. | | Regardless, unless a micropower transmitter is being used, it seems to me | that a very simple quarter wave nose tip made if 1/8" rod or similar | material would only protrude a few inches above the nose and would probably | do the job. At this frequency, even a tiny metal mass inside the nose would | probably be a sufficiently good counterpoise for feeding it. | | This seems like a simple problem (or 'no problem'). I'm surprised at the | complex solutions. | | Joe | W3JDR | | | wrote in message | ... | I've voulenteered to help the SDSU mechanical engineering studens get | telemetry from their rocket see: | http://www-rohan.sdsu.edu/~sharring/sdsurocket.html. | | I have all the electronics working, I'm using a commercial 910Mhz | telemetry radio, I have every thing working except the antenna. | | For the last launch I burred a dipole in the plywood fin, alas | the rocket did not launch it caught fire and burned up the fins. | (It did not burn as far as the electronics.) | | The new fins are carbon fiber composite so no antenna there... | | The rocket will get to mach 2 so small wires sticking out will | probably break or burn up. | | | I have enough power and ground side gain that I need no gain | from the rocket, an isotropic radiator with 3db of loss would be fine. | | | Any suggestions? | | | My ideas and thoughts: | | 1)Simple 1/4 wave vertical sticking out the bottom plate of the rocket | near the engine. | | Pros: | simple. | Cons: | lots of metal to block the signal and mess up the pattern. | Not clear if the ionized exhaust will block the signal. | Antenna pattern is almost exactly wrong. | | (Telemetry really needed for recovery tracking so ionization fading is | not a deal killer) | | | 2)Horizontal dipole at the bottom plate of engine. | All the problems of #1 except pattern. | | | | | 3)Put Fiberglass windows in the electronics bay near the nose of the | rocket. One window on each side, Driving two hosrizontal dipoles with | a power splitter, one dipole on each side. | | Pros: Easy to do. | Cons: | I don't know what the pattern would be like, or exactly how I shoudl | phase the two antennas on opposite sides. (Some metal between then so | not a clean situation.) | | Resources: | It have a minicircuits SMA 2 way power splitter, and can make precise | metal parts (0.002" or better). | I do not have any antenna testing equipment that is any good at | 900Mhz. | so any suggestions... | | | Paul (Kl7JG) | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
I forgot to include the part of his original post which suggested this to
me, here it is: "Antenna pattern is almost exactly wrong." ....when he was referring to a vertical antenna hanging from the tail (probably melt in the exhaust!) Warmest regards, John "John Smith" wrote in message ... | Doesn't his original post "indicate" he wishes a "horizontal" polarized ant, | as opposed to vertical nose rod? | | At least, that is why I dismissed the "obivious." | | Warmest regards, | John | | "W3JDR" wrote in message news:1cIee.3075$fQ2.31@trnddc05... || I'm surpised no one has asked how much transmit power is available, and | how || high the rocket is expected to fly. || || Regardless, unless a micropower transmitter is being used, it seems to me || that a very simple quarter wave nose tip made if 1/8" rod or similar || material would only protrude a few inches above the nose and would | probably || do the job. At this frequency, even a tiny metal mass inside the nose | would || probably be a sufficiently good counterpoise for feeding it. || || This seems like a simple problem (or 'no problem'). I'm surprised at the || complex solutions. || || Joe || W3JDR || || || wrote in message || ... || I've voulenteered to help the SDSU mechanical engineering studens get || telemetry from their rocket see: || http://www-rohan.sdsu.edu/~sharring/sdsurocket.html. || || I have all the electronics working, I'm using a commercial 910Mhz || telemetry radio, I have every thing working except the antenna. || || For the last launch I burred a dipole in the plywood fin, alas || the rocket did not launch it caught fire and burned up the fins. || (It did not burn as far as the electronics.) || || The new fins are carbon fiber composite so no antenna there... || || The rocket will get to mach 2 so small wires sticking out will || probably break or burn up. || || || I have enough power and ground side gain that I need no gain || from the rocket, an isotropic radiator with 3db of loss would be fine. || || || Any suggestions? || || || My ideas and thoughts: || || 1)Simple 1/4 wave vertical sticking out the bottom plate of the rocket || near the engine. || || Pros: || simple. || Cons: || lots of metal to block the signal and mess up the pattern. || Not clear if the ionized exhaust will block the signal. || Antenna pattern is almost exactly wrong. || || (Telemetry really needed for recovery tracking so ionization fading is || not a deal killer) || || || 2)Horizontal dipole at the bottom plate of engine. || All the problems of #1 except pattern. || || || || || 3)Put Fiberglass windows in the electronics bay near the nose of the || rocket. One window on each side, Driving two hosrizontal dipoles with || a power splitter, one dipole on each side. || || Pros: Easy to do. || Cons: || I don't know what the pattern would be like, or exactly how I shoudl || phase the two antennas on opposite sides. (Some metal between then so || not a clean situation.) || || Resources: || It have a minicircuits SMA 2 way power splitter, and can make precise || metal parts (0.002" or better). || I do not have any antenna testing equipment that is any good at || 900Mhz. || so any suggestions... || || || Paul (Kl7JG) || || || || || || || || || || || || || || || || || || || || || || || || || || || || || || || | | |
Dave:
He might be able to design the "fractal" as a "logo", serve a dual purpose!!! grin Warmest regards, John "Dave" wrote in message ... | nah, he needs a fractal patch or two. | | "Fred W4JLE" wrote in message | ... | You might take a look at slot antennas. | wrote in message | ... | I've voulenteered to help the SDSU mechanical engineering studens get | telemetry from their rocket see: | http://www-rohan.sdsu.edu/~sharring/sdsurocket.html. | | I have all the electronics working, I'm using a commercial 910Mhz | telemetry radio, I have every thing working except the antenna. | | For the last launch I burred a dipole in the plywood fin, alas | the rocket did not launch it caught fire and burned up the fins. | (It did not burn as far as the electronics.) | | The new fins are carbon fiber composite so no antenna there... | | The rocket will get to mach 2 so small wires sticking out will | probably break or burn up. | | | I have enough power and ground side gain that I need no gain | from the rocket, an isotropic radiator with 3db of loss would be fine. | | | Any suggestions? | | | My ideas and thoughts: | | 1)Simple 1/4 wave vertical sticking out the bottom plate of the rocket | near the engine. | | Pros: | simple. | Cons: | lots of metal to block the signal and mess up the pattern. | Not clear if the ionized exhaust will block the signal. | Antenna pattern is almost exactly wrong. | | (Telemetry really needed for recovery tracking so ionization fading is | not a deal killer) | | | 2)Horizontal dipole at the bottom plate of engine. | All the problems of #1 except pattern. | | | | | 3)Put Fiberglass windows in the electronics bay near the nose of the | rocket. One window on each side, Driving two hosrizontal dipoles with | a power splitter, one dipole on each side. | | Pros: Easy to do. | Cons: | I don't know what the pattern would be like, or exactly how I shoudl | phase the two antennas on opposite sides. (Some metal between then so | not a clean situation.) | | Resources: | It have a minicircuits SMA 2 way power splitter, and can make precise | metal parts (0.002" or better). | I do not have any antenna testing equipment that is any good at | 900Mhz. | so any suggestions... | | | Paul (Kl7JG) | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
wrote: I've voulenteered to help the SDSU mechanical engineering studens get telemetry from their rocket see: http://www-rohan.sdsu.edu/~sharring/sdsurocket.html. I have all the electronics working, I'm using a commercial 910Mhz telemetry radio, I have every thing working except the antenna. For the last launch I burred a dipole in the plywood fin, alas the rocket did not launch it caught fire and burned up the fins. (It did not burn as far as the electronics.) The new fins are carbon fiber composite so no antenna there... The rocket will get to mach 2 so small wires sticking out will probably break or burn up. I have enough power and ground side gain that I need no gain from the rocket, an isotropic radiator with 3db of loss would be fine. Any suggestions? http://www.psl.nmsu.edu/antennas/soundant.php http://www.psl.nmsu.edu/antennas/catalog.pdf Check out the slot wrap-around, and the micro-strip wrap-around antennas. ac6xg My ideas and thoughts: 1)Simple 1/4 wave vertical sticking out the bottom plate of the rocket near the engine. Pros: simple. Cons: lots of metal to block the signal and mess up the pattern. Not clear if the ionized exhaust will block the signal. Antenna pattern is almost exactly wrong. (Telemetry really needed for recovery tracking so ionization fading is not a deal killer) 2)Horizontal dipole at the bottom plate of engine. All the problems of #1 except pattern. 3)Put Fiberglass windows in the electronics bay near the nose of the rocket. One window on each side, Driving two hosrizontal dipoles with a power splitter, one dipole on each side. Pros: Easy to do. Cons: I don't know what the pattern would be like, or exactly how I shoudl phase the two antennas on opposite sides. (Some metal between then so not a clean situation.) Resources: It have a minicircuits SMA 2 way power splitter, and can make precise metal parts (0.002" or better). I do not have any antenna testing equipment that is any good at 900Mhz. so any suggestions... Paul (Kl7JG) |
Is it just me, or does "Mach II" suggest paint blistering speeds and plastic
melting frictions with air??? And, is that aluminum I see that rocket body made out of? Or, not? The carbon fiber just might absorb enough heat to keep a high temp coating from burning off copper foil... if the flight is of limited duration... Am I missing something or imagining "problems?" Warmest regards, John wrote in message ... | I've voulenteered to help the SDSU mechanical engineering studens get | telemetry from their rocket see: | http://www-rohan.sdsu.edu/~sharring/sdsurocket.html. | | I have all the electronics working, I'm using a commercial 910Mhz | telemetry radio, I have every thing working except the antenna. | | For the last launch I burred a dipole in the plywood fin, alas | the rocket did not launch it caught fire and burned up the fins. | (It did not burn as far as the electronics.) | | The new fins are carbon fiber composite so no antenna there... | | The rocket will get to mach 2 so small wires sticking out will | probably break or burn up. | | | I have enough power and ground side gain that I need no gain | from the rocket, an isotropic radiator with 3db of loss would be fine. | | | Any suggestions? | | | My ideas and thoughts: | | 1)Simple 1/4 wave vertical sticking out the bottom plate of the rocket | near the engine. | | Pros: | simple. | Cons: | lots of metal to block the signal and mess up the pattern. | Not clear if the ionized exhaust will block the signal. | Antenna pattern is almost exactly wrong. | | (Telemetry really needed for recovery tracking so ionization fading is | not a deal killer) | | | 2)Horizontal dipole at the bottom plate of engine. | All the problems of #1 except pattern. | | | | | 3)Put Fiberglass windows in the electronics bay near the nose of the | rocket. One window on each side, Driving two hosrizontal dipoles with | a power splitter, one dipole on each side. | | Pros: Easy to do. | Cons: | I don't know what the pattern would be like, or exactly how I shoudl | phase the two antennas on opposite sides. (Some metal between then so | not a clean situation.) | | Resources: | It have a minicircuits SMA 2 way power splitter, and can make precise | metal parts (0.002" or better). | I do not have any antenna testing equipment that is any good at | 900Mhz. | so any suggestions... | | | Paul (Kl7JG) | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
On Fri, 6 May 2005 10:09:00 -0700, "John Smith"
wrote: Doesn't his original post "indicate" he wishes a "horizontal" polarized ant, as opposed to vertical nose rod? What part of: "an isotropic radiator with 3db of loss would be fine" do you have a problem with? |
I define true "isotropic" as impossible... perhaps a sphere as an
antenna--in space... I define "3db of loss" as the "minimum acceptable", not the desired... Got anymore hairs to split, I got my "hair-splitter" out, no problem really... Regards, John "Wes Stewart" wrote in message ... | On Fri, 6 May 2005 10:09:00 -0700, "John Smith" | wrote: | | Doesn't his original post "indicate" he wishes a "horizontal" polarized ant, | as opposed to vertical nose rod? | | What part of: "an isotropic radiator with 3db of loss would be fine" | do you have a problem with? |
On Fri, 6 May 2005 10:28:17 -0400, "Fred W4JLE"
wrote: You might take a look at slot antennas. wrote in message .. . I've voulenteered to help the SDSU mechanical engineering studens get telemetry from their rocket see: http://www-rohan.sdsu.edu/~sharring/sdsurocket.html. I have all the electronics working, I'm using a commercial 910Mhz telemetry radio, I have every thing working except the antenna. Fred has the right idea given the construction materials, and the need for obstruction-free (much less friction-free) elements. However, no one has actually responded to your concern about pattern. With you or your trackers occupying the area directly below the rising rocket, this places you in the null of a vertically polarized antenna of conventional length. However, if you lengthen the radiator to several wavelengths, this will produce radiation lobes that reach down toward ground control, rather than out towards the horizon (where you are not). 73's Richard Clark, KB7QHC |
On Thu, 05 May 2005 21:43:43 -0700, wrote:
I've voulenteered to help the SDSU mechanical engineering studens get telemetry from their rocket see: http://www-rohan.sdsu.edu/~sharring/sdsurocket.html. I have all the electronics working, I'm using a commercial 910Mhz telemetry radio, I have every thing working except the antenna. For the last launch I burred a dipole in the plywood fin, alas the rocket did not launch it caught fire and burned up the fins. (It did not burn as far as the electronics.) The new fins are carbon fiber composite so no antenna there... The rocket will get to mach 2 so small wires sticking out will probably break or burn up. I have enough power and ground side gain that I need no gain from the rocket, an isotropic radiator with 3db of loss would be fine. Any suggestions? My ideas and thoughts: 1)Simple 1/4 wave vertical sticking out the bottom plate of the rocket near the engine. Pros: simple. Cons: lots of metal to block the signal and mess up the pattern. Not clear if the ionized exhaust will block the signal. Phoenix, Standard and other missiles use rear data link antennas buried behind the rocket plume without trouble. Of course these are at X-band, not 900 MHz, and receive only with *really* high powered transmitters. Antenna pattern is almost exactly wrong. (Telemetry really needed for recovery tracking so ionization fading is not a deal killer) 2)Horizontal dipole at the bottom plate of engine. All the problems of #1 except pattern. 3)Put Fiberglass windows in the electronics bay near the nose of the rocket. One window on each side, Driving two hosrizontal dipoles with a power splitter, one dipole on each side. Pros: Easy to do. Cons: I don't know what the pattern would be like, or exactly how I shoudl phase the two antennas on opposite sides. (Some metal between then so not a clean situation.) Resources: It have a minicircuits SMA 2 way power splitter, and can make precise metal parts (0.002" or better). I do not have any antenna testing equipment that is any good at 900Mhz. so any suggestions... Well, the fact that you don't have any test equipment is a real downer. The best suggestion, although I think time is an issue for you, would be to go to a commercial vendor and beg for a "contribution". My former employer (Hughes) gave money, time and materials to various universities all of the time. The elegant solution would be a conformal patch but I imagine this is beyond your resources. http://www.uaf.edu/asgp/asrp/srp4/sr...chantennas.htm It doesn't look like there is any roll stabilization so you might need some pseudo "omni" pattern, during flight. But if you are only looking for TM after burnout and during the return to Earth (I assume dangling on a parachute) then you will know the attitude (at least "up" and "down"). Personally, I think that flight dynamics data during the powered phase would be more interesting to engineering students. [g]. Fiberglass window(s) with dipole(s) behind them would probably work okay. Two with equal power split would be fine, however, one might do okay too. Regardless, it sounds like a fun project. Have fun. |
Thanks for all the fine suggestions.
Some general comments and answers to questions...: 1)The body of the rocket is Aluminum. 2)The receiving station is right next to the rocket so as it launches it will be going directly away from the telemetry transmitter. 3)The nose cone is out as it detaches and comes down via seperate parachute at the time of recovery. 4)No roll control system so the rocket will be expected to spin slowly. 5)1W of output power. It looks like a cu tape dipole on the fin with some glass over the top might be best solution, it seems no one but me is worried about the carbon fiber. So using 1/4" cu Tape glued to carbon fiber ,how long should it be and should the ends be round, square or pointed? (910 Mhz) The rocket has three fins 120 degrees apart, could I put an antenna on two fins and get quasi circular polarization? If so how should I drive the two antennas? (I'm not an antenna guy so please try and be specific, ie use a 21.5cm peice of Rg-XX) I have no portable antenna test quipment for 910Mhz, but I can carry the resulant antenna into a friends work and use a 2Ghz spectrum analizer with a tracking generator if that would be useful to test antennas. If I have just one fin antenna how can I build a circularly polarized antenna for the ground side? (I presently have a 8dbd loop yagi for the receiver, H or V polarization, not ciurcular..) On Fri, 06 May 2005 14:29:27 -0700, Wes Stewart wrote: On Thu, 05 May 2005 21:43:43 -0700, wrote: I've voulenteered to help the SDSU mechanical engineering studens get telemetry from their rocket see: http://www-rohan.sdsu.edu/~sharring/sdsurocket.html. I have all the electronics working, I'm using a commercial 910Mhz telemetry radio, I have every thing working except the antenna. For the last launch I burred a dipole in the plywood fin, alas the rocket did not launch it caught fire and burned up the fins. (It did not burn as far as the electronics.) The new fins are carbon fiber composite so no antenna there... The rocket will get to mach 2 so small wires sticking out will probably break or burn up. I have enough power and ground side gain that I need no gain from the rocket, an isotropic radiator with 3db of loss would be fine. Any suggestions? My ideas and thoughts: 1)Simple 1/4 wave vertical sticking out the bottom plate of the rocket near the engine. Pros: simple. Cons: lots of metal to block the signal and mess up the pattern. Not clear if the ionized exhaust will block the signal. Phoenix, Standard and other missiles use rear data link antennas buried behind the rocket plume without trouble. Of course these are at X-band, not 900 MHz, and receive only with *really* high powered transmitters. Antenna pattern is almost exactly wrong. (Telemetry really needed for recovery tracking so ionization fading is not a deal killer) 2)Horizontal dipole at the bottom plate of engine. All the problems of #1 except pattern. 3)Put Fiberglass windows in the electronics bay near the nose of the rocket. One window on each side, Driving two hosrizontal dipoles with a power splitter, one dipole on each side. Pros: Easy to do. Cons: I don't know what the pattern would be like, or exactly how I shoudl phase the two antennas on opposite sides. (Some metal between then so not a clean situation.) Resources: It have a minicircuits SMA 2 way power splitter, and can make precise metal parts (0.002" or better). I do not have any antenna testing equipment that is any good at 900Mhz. so any suggestions... Well, the fact that you don't have any test equipment is a real downer. The best suggestion, although I think time is an issue for you, would be to go to a commercial vendor and beg for a "contribution". My former employer (Hughes) gave money, time and materials to various universities all of the time. The elegant solution would be a conformal patch but I imagine this is beyond your resources. http://www.uaf.edu/asgp/asrp/srp4/sr...chantennas.htm It doesn't look like there is any roll stabilization so you might need some pseudo "omni" pattern, during flight. But if you are only looking for TM after burnout and during the return to Earth (I assume dangling on a parachute) then you will know the attitude (at least "up" and "down"). Personally, I think that flight dynamics data during the powered phase would be more interesting to engineering students. [g]. Fiberglass window(s) with dipole(s) behind them would probably work okay. Two with equal power split would be fine, however, one might do okay too. Regardless, it sounds like a fun project. Have fun. |
Well, I just a new experimenter with antennas--in the past have only played
with "tried and true" designs.... However, I can't help but see that three cu foil horizontal "monopoles" worked off an aluminum body of the rocket does present itself to the mind... Cecil is a good modeler with EZNEC, I am hoping he will find this interesting enough to comment... and of course the OM Roy is acknowledged top expert! If three monopoles, each fed off a quarter matching section of thin coax, and worked off the counterpoise of the aluminum rocket body "counterpoise", would present a load of say ~11 ohms (or, does it work that way? or, would that present a load of ~36 ohms?), then a 4:1 UnUn could be used, "backwards", to present a 44 ohm to the xmitter--50/44 = negligible SWR... one monopole on each fin.... While NOT circular--maybe close enough to provide acceptable signal strength... If this is plausible, a formula for cutting a 1/4 wave as SHF, and cut a bit longer, then trimmed to resonance by coupling to a GDO capable of 900+ Mhz.... But, you are probably too close to launch time for extensive experimentation... or, are some of those students' hams to assist? But then, my mom always said I read too much "science fiction." Maybe these other guys will apply their knowledge here and both you and I will pick up some points... On a side note, two crossed dipoles make a turnstile antenna, this is a circular polarized antenna... but crossing two of those fins is impossible... maybe the dipoles can be separated by some distance and still work... here I can only wonder... indeed, if you choose this, would be a shame to leave that third fin out there, naked... grin Whatever, GOOD LUCK!!! Warmest regards, John wrote in message ... | Thanks for all the fine suggestions. | Some general comments and answers to questions...: | | 1)The body of the rocket is Aluminum. | | 2)The receiving station is right next to the rocket so as it launches | it will be going directly away from the telemetry transmitter. | | 3)The nose cone is out as it detaches and comes down via seperate | parachute at the time of recovery. | | 4)No roll control system so the rocket will be expected to spin | slowly. | | 5)1W of output power. | | | It looks like a cu tape dipole on the fin with some glass over the top | might be best solution, it seems no one but me is worried about the | carbon fiber. | | So using 1/4" cu Tape glued to carbon fiber ,how long should it be | and should the ends be round, square or pointed? (910 Mhz) | | | The rocket has three fins 120 degrees apart, could I put an antenna on | two fins and get quasi circular polarization? | If so how should I drive the two antennas? | (I'm not an antenna guy so please try and be specific, ie use a 21.5cm | peice of Rg-XX) | | I have no portable antenna test quipment for 910Mhz, but I can carry | the resulant antenna into a friends work and use a 2Ghz spectrum | analizer with a tracking generator if that would be useful to test | antennas. | | | | If I have just one fin antenna how can I build a circularly polarized | antenna for the ground side? | (I presently have a 8dbd loop yagi for the receiver, H or V | polarization, not ciurcular..) | | | | | | | | | | | | | | | | On Fri, 06 May 2005 14:29:27 -0700, Wes Stewart | wrote: | | On Thu, 05 May 2005 21:43:43 -0700, wrote: | | I've voulenteered to help the SDSU mechanical engineering studens get | telemetry from their rocket see: | http://www-rohan.sdsu.edu/~sharring/sdsurocket.html. | | I have all the electronics working, I'm using a commercial 910Mhz | telemetry radio, I have every thing working except the antenna. | | For the last launch I burred a dipole in the plywood fin, alas | the rocket did not launch it caught fire and burned up the fins. | (It did not burn as far as the electronics.) | | The new fins are carbon fiber composite so no antenna there... | | The rocket will get to mach 2 so small wires sticking out will | probably break or burn up. | | | I have enough power and ground side gain that I need no gain | from the rocket, an isotropic radiator with 3db of loss would be fine. | | | Any suggestions? | | | My ideas and thoughts: | | 1)Simple 1/4 wave vertical sticking out the bottom plate of the rocket | near the engine. | | Pros: | simple. | Cons: | lots of metal to block the signal and mess up the pattern. | Not clear if the ionized exhaust will block the signal. | | Phoenix, Standard and other missiles use rear data link antennas | buried behind the rocket plume without trouble. Of course these are | at X-band, not 900 MHz, and receive only with *really* high powered | transmitters. | | Antenna pattern is almost exactly wrong. | | (Telemetry really needed for recovery tracking so ionization fading is | not a deal killer) | | | 2)Horizontal dipole at the bottom plate of engine. | All the problems of #1 except pattern. | | | | | 3)Put Fiberglass windows in the electronics bay near the nose of the | rocket. One window on each side, Driving two hosrizontal dipoles with | a power splitter, one dipole on each side. | | Pros: Easy to do. | Cons: | I don't know what the pattern would be like, or exactly how I shoudl | phase the two antennas on opposite sides. (Some metal between then so | not a clean situation.) | | Resources: | It have a minicircuits SMA 2 way power splitter, and can make precise | metal parts (0.002" or better). | I do not have any antenna testing equipment that is any good at | 900Mhz. | so any suggestions... | | Well, the fact that you don't have any test equipment is a real | downer. | | The best suggestion, although I think time is an issue for you, would | be to go to a commercial vendor and beg for a "contribution". My | former employer (Hughes) gave money, time and materials to various | universities all of the time. | | The elegant solution would be a conformal patch but I imagine this is | beyond your resources. | | http://www.uaf.edu/asgp/asrp/srp4/sr...chantennas.htm | | It doesn't look like there is any roll stabilization so you might need | some pseudo "omni" pattern, during flight. But if you are only | looking for TM after burnout and during the return to Earth (I assume | dangling on a parachute) then you will know the attitude (at least | "up" and "down"). Personally, I think that flight dynamics data | during the powered phase would be more interesting to engineering | students. [g]. | | Fiberglass window(s) with dipole(s) behind them would probably work | okay. Two with equal power split would be fine, however, one might do | okay too. | | Regardless, it sounds like a fun project. Have fun. | |
SWR is not a concern. You may be interested to know that 17:1 SWR was pretty
common in many of the satellite antennas. As they are interested in signals as the rocket is going away, an end fed "longwire" would do just fine. Were it my project, I would use 4 slotted antennas cut at 45 degrees to the axis of flight. Particularly because the rocket is not spin stabilized. While Mach 2 was mentioned, I suspect it would exist for a very short time. Standard Plexiglas would most likely serve well as a slot cover. "John Smith" wrote in message ... Well, I just a new experimenter with antennas--in the past have only played with "tried and true" designs.... However, I can't help but see that three cu foil horizontal "monopoles" worked off an aluminum body of the rocket does present itself to the mind... Cecil is a good modeler with EZNEC, I am hoping he will find this interesting enough to comment... and of course the OM Roy is acknowledged top expert! If three monopoles, each fed off a quarter matching section of thin coax, and worked off the counterpoise of the aluminum rocket body "counterpoise", would present a load of say ~11 ohms (or, does it work that way? or, would that present a load of ~36 ohms?), then a 4:1 UnUn could be used, "backwards", to present a 44 ohm to the xmitter--50/44 = negligible SWR... one monopole on each fin.... While NOT circular--maybe close enough to provide acceptable signal strength... If this is plausible, a formula for cutting a 1/4 wave as SHF, and cut a bit longer, then trimmed to resonance by coupling to a GDO capable of 900+ Mhz.... But, you are probably too close to launch time for extensive experimentation... or, are some of those students' hams to assist? But then, my mom always said I read too much "science fiction." Maybe these other guys will apply their knowledge here and both you and I will pick up some points... On a side note, two crossed dipoles make a turnstile antenna, this is a circular polarized antenna... but crossing two of those fins is impossible... maybe the dipoles can be separated by some distance and still work... here I can only wonder... indeed, if you choose this, would be a shame to leave that third fin out there, naked... grin Whatever, GOOD LUCK!!! Warmest regards, John wrote in message ... | Thanks for all the fine suggestions. | Some general comments and answers to questions...: | | 1)The body of the rocket is Aluminum. | | 2)The receiving station is right next to the rocket so as it launches | it will be going directly away from the telemetry transmitter. | | 3)The nose cone is out as it detaches and comes down via seperate | parachute at the time of recovery. | | 4)No roll control system so the rocket will be expected to spin | slowly. | | 5)1W of output power. | | | It looks like a cu tape dipole on the fin with some glass over the top | might be best solution, it seems no one but me is worried about the | carbon fiber. | | So using 1/4" cu Tape glued to carbon fiber ,how long should it be | and should the ends be round, square or pointed? (910 Mhz) | | | The rocket has three fins 120 degrees apart, could I put an antenna on | two fins and get quasi circular polarization? | If so how should I drive the two antennas? | (I'm not an antenna guy so please try and be specific, ie use a 21.5cm | peice of Rg-XX) | | I have no portable antenna test quipment for 910Mhz, but I can carry | the resulant antenna into a friends work and use a 2Ghz spectrum | analizer with a tracking generator if that would be useful to test | antennas. | | | | If I have just one fin antenna how can I build a circularly polarized | antenna for the ground side? | (I presently have a 8dbd loop yagi for the receiver, H or V | polarization, not ciurcular..) | | | | | | | | | | | | | | | | On Fri, 06 May 2005 14:29:27 -0700, Wes Stewart | wrote: | | On Thu, 05 May 2005 21:43:43 -0700, wrote: | | I've voulenteered to help the SDSU mechanical engineering studens get | telemetry from their rocket see: | http://www-rohan.sdsu.edu/~sharring/sdsurocket.html. | | I have all the electronics working, I'm using a commercial 910Mhz | telemetry radio, I have every thing working except the antenna. | | For the last launch I burred a dipole in the plywood fin, alas | the rocket did not launch it caught fire and burned up the fins. | (It did not burn as far as the electronics.) | | The new fins are carbon fiber composite so no antenna there... | | The rocket will get to mach 2 so small wires sticking out will | probably break or burn up. | | | I have enough power and ground side gain that I need no gain | from the rocket, an isotropic radiator with 3db of loss would be fine. | | | Any suggestions? | | | My ideas and thoughts: | | 1)Simple 1/4 wave vertical sticking out the bottom plate of the rocket | near the engine. | | Pros: | simple. | Cons: | lots of metal to block the signal and mess up the pattern. | Not clear if the ionized exhaust will block the signal. | | Phoenix, Standard and other missiles use rear data link antennas | buried behind the rocket plume without trouble. Of course these are | at X-band, not 900 MHz, and receive only with *really* high powered | transmitters. | | Antenna pattern is almost exactly wrong. | | (Telemetry really needed for recovery tracking so ionization fading is | not a deal killer) | | | 2)Horizontal dipole at the bottom plate of engine. | All the problems of #1 except pattern. | | | | | 3)Put Fiberglass windows in the electronics bay near the nose of the | rocket. One window on each side, Driving two hosrizontal dipoles with | a power splitter, one dipole on each side. | | Pros: Easy to do. | Cons: | I don't know what the pattern would be like, or exactly how I shoudl | phase the two antennas on opposite sides. (Some metal between then so | not a clean situation.) | | Resources: | It have a minicircuits SMA 2 way power splitter, and can make precise | metal parts (0.002" or better). | I do not have any antenna testing equipment that is any good at | 900Mhz. | so any suggestions... | | Well, the fact that you don't have any test equipment is a real | downer. | | The best suggestion, although I think time is an issue for you, would | be to go to a commercial vendor and beg for a "contribution". My | former employer (Hughes) gave money, time and materials to various | universities all of the time. | | The elegant solution would be a conformal patch but I imagine this is | beyond your resources. | | http://www.uaf.edu/asgp/asrp/srp4/sr...chantennas.htm | | It doesn't look like there is any roll stabilization so you might need | some pseudo "omni" pattern, during flight. But if you are only | looking for TM after burnout and during the return to Earth (I assume | dangling on a parachute) then you will know the attitude (at least | "up" and "down"). Personally, I think that flight dynamics data | during the powered phase would be more interesting to engineering | students. [g]. | | Fiberglass window(s) with dipole(s) behind them would probably work | okay. Two with equal power split would be fine, however, one might do | okay too. | | Regardless, it sounds like a fun project. Have fun. | |
I am just out of my field here (never stopped my comments yet grin) but,
symmetry seems to be the key here… Others are often having greater luck than me; however, I have great respect for Mr. Murphys’ law. If I were to hang a long wire (even at near Ghz freqs.) off a single fin, having constructed it from “wire” hefty enough to take mach speeds with ease, I would worry about drag. While that long-wire may not end up taking on the weight of an elephant, I would take it for granted it could be measured in ounces, indeed, I expect pounds are quite possible… This does not suggest itself favorable to “straight as an arrow” flight… Warmest regards, John "Fred W4JLE" wrote in message ... | SWR is not a concern. You may be interested to know that 17:1 SWR was pretty | common in many of the satellite antennas. | | As they are interested in signals as the rocket is going away, an end fed | "longwire" would do just fine. | | Were it my project, I would use 4 slotted antennas cut at 45 degrees to the | axis of flight. Particularly because the rocket is not spin stabilized. | While Mach 2 was mentioned, I suspect it would exist for a very short time. | Standard Plexiglas would most likely serve well as a slot cover. | | | | "John Smith" wrote in message | ... | Well, I just a new experimenter with antennas--in the past have only | played | with "tried and true" designs.... | | | | However, I can't help but see that three cu foil horizontal "monopoles" | worked off an aluminum body of the rocket does present itself to the | mind... | | | | Cecil is a good modeler with EZNEC, I am hoping he will find this | interesting enough to comment... and of course the OM Roy is acknowledged | top expert! | | | | If three monopoles, each fed off a quarter matching section of thin coax, | and worked off the counterpoise of the aluminum rocket body | "counterpoise", | would present a load of say ~11 ohms (or, does it work that way? or, would | that present a load of ~36 ohms?), then a 4:1 UnUn could be used, | "backwards", to present a 44 ohm to the xmitter--50/44 = negligible SWR... | one monopole on each fin.... | | While NOT circular--maybe close enough to provide acceptable signal | strength... | | | | If this is plausible, a formula for cutting a 1/4 wave as SHF, and cut a | bit | longer, then trimmed to resonance by coupling to a GDO capable of 900+ | Mhz.... | | | | But, you are probably too close to launch time for extensive | experimentation... or, are some of those students' hams to assist? | | | | But then, my mom always said I read too much "science fiction." | | | | Maybe these other guys will apply their knowledge here and both you and I | will pick up some points... | | | | On a side note, two crossed dipoles make a turnstile antenna, this is a | circular polarized antenna... but crossing two of those fins is | impossible... maybe the dipoles can be separated by some distance and | still | work... here I can only wonder... indeed, if you choose this, would be a | shame to leave that third fin out there, naked... grin | | | | Whatever, GOOD LUCK!!! | | | | Warmest regards, | | John | | | | | wrote in message | ... | | Thanks for all the fine suggestions. | | Some general comments and answers to questions...: | | | | 1)The body of the rocket is Aluminum. | | | | 2)The receiving station is right next to the rocket so as it launches | | it will be going directly away from the telemetry transmitter. | | | | 3)The nose cone is out as it detaches and comes down via seperate | | parachute at the time of recovery. | | | | 4)No roll control system so the rocket will be expected to spin | | slowly. | | | | 5)1W of output power. | | | | | | It looks like a cu tape dipole on the fin with some glass over the top | | might be best solution, it seems no one but me is worried about the | | carbon fiber. | | | | So using 1/4" cu Tape glued to carbon fiber ,how long should it be | | and should the ends be round, square or pointed? (910 Mhz) | | | | | | The rocket has three fins 120 degrees apart, could I put an antenna on | | two fins and get quasi circular polarization? | | If so how should I drive the two antennas? | | (I'm not an antenna guy so please try and be specific, ie use a 21.5cm | | peice of Rg-XX) | | | | I have no portable antenna test quipment for 910Mhz, but I can carry | | the resulant antenna into a friends work and use a 2Ghz spectrum | | analizer with a tracking generator if that would be useful to test | | antennas. | | | | | | | | If I have just one fin antenna how can I build a circularly polarized | | antenna for the ground side? | | (I presently have a 8dbd loop yagi for the receiver, H or V | | polarization, not ciurcular..) | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | On Fri, 06 May 2005 14:29:27 -0700, Wes Stewart | | wrote: | | | | On Thu, 05 May 2005 21:43:43 -0700, wrote: | | | | I've voulenteered to help the SDSU mechanical engineering studens get | | telemetry from their rocket see: | | http://www-rohan.sdsu.edu/~sharring/sdsurocket.html. | | | | I have all the electronics working, I'm using a commercial 910Mhz | | telemetry radio, I have every thing working except the antenna. | | | | For the last launch I burred a dipole in the plywood fin, alas | | the rocket did not launch it caught fire and burned up the fins. | | (It did not burn as far as the electronics.) | | | | The new fins are carbon fiber composite so no antenna there... | | | | The rocket will get to mach 2 so small wires sticking out will | | probably break or burn up. | | | | | | I have enough power and ground side gain that I need no gain | | from the rocket, an isotropic radiator with 3db of loss would be fine. | | | | | | Any suggestions? | | | | | | My ideas and thoughts: | | | | 1)Simple 1/4 wave vertical sticking out the bottom plate of the rocket | | near the engine. | | | | Pros: | | simple. | | Cons: | | lots of metal to block the signal and mess up the pattern. | | Not clear if the ionized exhaust will block the signal. | | | | Phoenix, Standard and other missiles use rear data link antennas | | buried behind the rocket plume without trouble. Of course these are | | at X-band, not 900 MHz, and receive only with *really* high powered | | transmitters. | | | | Antenna pattern is almost exactly wrong. | | | | (Telemetry really needed for recovery tracking so ionization fading is | | not a deal killer) | | | | | | 2)Horizontal dipole at the bottom plate of engine. | | All the problems of #1 except pattern. | | | | | | | | | | 3)Put Fiberglass windows in the electronics bay near the nose of the | | rocket. One window on each side, Driving two hosrizontal dipoles with | | a power splitter, one dipole on each side. | | | | Pros: Easy to do. | | Cons: | | I don't know what the pattern would be like, or exactly how I shoudl | | phase the two antennas on opposite sides. (Some metal between then so | | not a clean situation.) | | | | Resources: | | It have a minicircuits SMA 2 way power splitter, and can make precise | | metal parts (0.002" or better). | | I do not have any antenna testing equipment that is any good at | | 900Mhz. | | so any suggestions... | | | | Well, the fact that you don't have any test equipment is a real | | downer. | | | | The best suggestion, although I think time is an issue for you, would | | be to go to a commercial vendor and beg for a "contribution". My | | former employer (Hughes) gave money, time and materials to various | | universities all of the time. | | | | The elegant solution would be a conformal patch but I imagine this is | | beyond your resources. | | | | | http://www.uaf.edu/asgp/asrp/srp4/sr...chantennas.htm | | | | It doesn't look like there is any roll stabilization so you might need | | some pseudo "omni" pattern, during flight. But if you are only | | looking for TM after burnout and during the return to Earth (I assume | | dangling on a parachute) then you will know the attitude (at least | | "up" and "down"). Personally, I think that flight dynamics data | | during the powered phase would be more interesting to engineering | | students. [g]. | | | | Fiberglass window(s) with dipole(s) behind them would probably work | | okay. Two with equal power split would be fine, however, one might do | | okay too. | | | | Regardless, it sounds like a fun project. Have fun. | | | | | | |
|
Well, let's just kick back and relax--after all-we are not dealing with
"Rocket Scientists" here.... OHH! Wait a minute--WE ARE!!!! grin Warmest regards, John wrote in message ... | I've voulenteered to help the SDSU mechanical engineering studens get | telemetry from their rocket see: | http://www-rohan.sdsu.edu/~sharring/sdsurocket.html. | | I have all the electronics working, I'm using a commercial 910Mhz | telemetry radio, I have every thing working except the antenna. | | For the last launch I burred a dipole in the plywood fin, alas | the rocket did not launch it caught fire and burned up the fins. | (It did not burn as far as the electronics.) | | The new fins are carbon fiber composite so no antenna there... | | The rocket will get to mach 2 so small wires sticking out will | probably break or burn up. | | | I have enough power and ground side gain that I need no gain | from the rocket, an isotropic radiator with 3db of loss would be fine. | | | Any suggestions? | | | My ideas and thoughts: | | 1)Simple 1/4 wave vertical sticking out the bottom plate of the rocket | near the engine. | | Pros: | simple. | Cons: | lots of metal to block the signal and mess up the pattern. | Not clear if the ionized exhaust will block the signal. | Antenna pattern is almost exactly wrong. | | (Telemetry really needed for recovery tracking so ionization fading is | not a deal killer) | | | 2)Horizontal dipole at the bottom plate of engine. | All the problems of #1 except pattern. | | | | | 3)Put Fiberglass windows in the electronics bay near the nose of the | rocket. One window on each side, Driving two hosrizontal dipoles with | a power splitter, one dipole on each side. | | Pros: Easy to do. | Cons: | I don't know what the pattern would be like, or exactly how I shoudl | phase the two antennas on opposite sides. (Some metal between then so | not a clean situation.) | | Resources: | It have a minicircuits SMA 2 way power splitter, and can make precise | metal parts (0.002" or better). | I do not have any antenna testing equipment that is any good at | 900Mhz. | so any suggestions... | | | Paul (Kl7JG) | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Paul:
If you don't mind, I would have a question for you (or, if you would be so kind as to pose it to a college there)--one I have always pondered... Take your rocket there, if its top speed is mach II--why not--say at mach-one, release the fins in a simultaneous-organized-precise manner--ridding the rocket of the leading fin edge drag--and hopefully--allowing it to reach a greater max speed/altitude... Wouldn't the "steering" of the air drag on the sides of the body provide enough "control" at such speeds or, even sub-mach speeds--possibly? Of course, if that antenna is there... grin Warmest regards, John wrote in message ... | I've voulenteered to help the SDSU mechanical engineering studens get | telemetry from their rocket see: | http://www-rohan.sdsu.edu/~sharring/sdsurocket.html. | | I have all the electronics working, I'm using a commercial 910Mhz | telemetry radio, I have every thing working except the antenna. | | For the last launch I burred a dipole in the plywood fin, alas | the rocket did not launch it caught fire and burned up the fins. | (It did not burn as far as the electronics.) | | The new fins are carbon fiber composite so no antenna there... | | The rocket will get to mach 2 so small wires sticking out will | probably break or burn up. | | | I have enough power and ground side gain that I need no gain | from the rocket, an isotropic radiator with 3db of loss would be fine. | | | Any suggestions? | | | My ideas and thoughts: | | 1)Simple 1/4 wave vertical sticking out the bottom plate of the rocket | near the engine. | | Pros: | simple. | Cons: | lots of metal to block the signal and mess up the pattern. | Not clear if the ionized exhaust will block the signal. | Antenna pattern is almost exactly wrong. | | (Telemetry really needed for recovery tracking so ionization fading is | not a deal killer) | | | 2)Horizontal dipole at the bottom plate of engine. | All the problems of #1 except pattern. | | | | | 3)Put Fiberglass windows in the electronics bay near the nose of the | rocket. One window on each side, Driving two hosrizontal dipoles with | a power splitter, one dipole on each side. | | Pros: Easy to do. | Cons: | I don't know what the pattern would be like, or exactly how I shoudl | phase the two antennas on opposite sides. (Some metal between then so | not a clean situation.) | | Resources: | It have a minicircuits SMA 2 way power splitter, and can make precise | metal parts (0.002" or better). | I do not have any antenna testing equipment that is any good at | 900Mhz. | so any suggestions... | | | Paul (Kl7JG) | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
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