View Single Post
  #4   Report Post  
Old May 6th 05, 07:26 AM
John Smith
 
Posts: n/a
Default

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)
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|