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)
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