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)
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