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.
|