May 7th 05, 05:31 PM
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On Fri, 06 May 2005 19:23:55 -0700, wrote:
Thanks for all the fine suggestions.
Some general comments and answers to questions...:
1)The body of the rocket is Aluminum.
Figured that.
2)The receiving station is right next to the rocket so as it launches
it will be going directly away from the telemetry transmitter.
Not too close I hope [g].
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.
I didn't say that. I'm not a composites man, but it seems to me that
"carbon fiber" is a pretty broad catagory, with potentially a wide
range of dielectric properties. When you attach your radiator, of
whatever kind, to a dielectric substrate the electrical properties are
going to be affected to some degree.
If by experiment (something you are without the means to do) you find
the proper length for your dipole, then when you encapuslate it in
glass fiber, you have added a second dielectric.
And then... how do you attach the transmission line? I presume that
the line will be inside a hollow fin but you have to make a connection
to a foil that, until it is covered with the overlay, is on the
outside of the fin. Even if you succeed in the attachment, at Mach 2
this is not a benign enviroment. I suspect a lot of vibration. A
soldered connection might fail. In industry, we would shake the hell
out of the thing to see what happens.
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)
See above. Can't say.
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)
As you've seen, being "specific" isn't going to happen. I think you
have enough trouble without trying to achieve circular polarization,
something that doesn't seem to be a requirement anyway.
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.
No help unless you can use a reflection bridge, driven by the
generator and sampled by the SA. Otherwise, these are useful for
insertion measurements only.
If I have just one fin antenna how can I build a circularly polarized
antenna for the ground side?
The axial-mode helix would normally seem to be the antenna of choice.
They are forgiving designs and of reasonable size at 900 MHz. Do not
expect the gain that is rumored by Kraus. However, one expects that
the missile goes "downrange" so if you want recovery data down to the
ground then you might need some tracking using a gain antenna.
An option might be a turnstile over a groundplane that can give
circular polarization and a nearly omni pattern down to the horizon.
But if you achieve the 100 mile altitude and depending on when the
parachute is deployed and winds aloft, "downrange" might be quite a
distance. You need to do some link budget calculations for this.
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