I am just out of my field here (never stopped my comments yet grin) but,
symmetry seems to be the key here…



Others are often having greater luck than me; however, I have great respect
for Mr. Murphys’ law.



If I were to hang a long wire (even at near Ghz freqs.) off a single fin,
having constructed it from “wire” hefty enough to take mach speeds with
ease, I would worry about drag.



While that long-wire may not end up taking on the weight of an elephant, I
would take it for granted it could be measured in ounces, indeed, I expect
pounds are quite possible…



This does not suggest itself favorable to “straight as an arrow” flight…



Warmest regards,

John

"Fred W4JLE" wrote in message
...
| 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.
| |
|
|
|
|

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.

Well, let's just kick back and relax--after all-we are not dealing with
"Rocket Scientists" here....

OHH! Wait a minute--WE ARE!!!! grin

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

Paul:



If you don't mind, I would have a question for you (or, if you would be so
kind as to pose it to a college there)--one I have always pondered...



Take your rocket there, if its top speed is mach II--why not--say at
mach-one, release the fins in a simultaneous-organized-precise
manner--ridding the rocket of the leading fin edge drag--and
hopefully--allowing it to reach a greater max speed/altitude...



Wouldn't the "steering" of the air drag on the sides of the body provide
enough "control" at such speeds or, even sub-mach speeds--possibly?



Of course, if that antenna is there... grin



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