I'm still playing with the rocket antenna.
The rocket body is a 12 inch diameter aluminum tube.

If I want to put a horzintal dipole on the body I can do one of two
things.


1)Cut an Oval or oblong hole in the skin up near the electronics and
then put in a fibnerglass panel, on that panel I put a cu foil dipole.

How much bigger does the opening around the dipole have to be to not
reduce the efficency of the antenna.

2)I can put a thin dialectric patch on the outside of the rocket and
put the antenna on that.
How thick would a fiberglass dielectric need to be for a good antenna?



I now have a 900Mhz capable bird so I can trim the antenna for minimum
SWR.

This sunday is my last chance to make all of this work so I'm running
out of time.


Paul (Kl7JG)

wrote in message
...
I'm still playing with the rocket antenna.
The rocket body is a 12 inch diameter aluminum tube.

If I want to put a horzintal dipole on the body I can do one of two
things.


1)Cut an Oval or oblong hole in the skin up near the electronics and
then put in a fibnerglass panel, on that panel I put a cu foil dipole.

How much bigger does the opening around the dipole have to be to not
reduce the efficency of the antenna.

2)I can put a thin dialectric patch on the outside of the rocket and
put the antenna on that.
How thick would a fiberglass dielectric need to be for a good antenna?



I now have a 900Mhz capable bird so I can trim the antenna for minimum
SWR.

This sunday is my last chance to make all of this work so I'm running
out of time.


Paul (Kl7JG)

Since you are considering cutting holes in the body, I would suggest a
vertical slot dipole antenna, which at 900 MHz is 6.25" long -- not sure on
the slot width, but it is lambda/2. A vertical slot has a horizontally
polarized radiation pattern. You may consider 2 or 3 vertical slots fed
from a splitter to ensure complete coverage. This is a similar arrangement
as used by ground based VORs -- a VHF aviation navaid. Radiation directly
below the rocket is at a minimum, as it probably will be with any antenna.

73,

Frank

10-9-8-7-6-5-4-3-2-1... Houston, we have a problem... hopefully NOT!

Warmest regards,
John
--
Sit down the six-pack!!! STEP AWAY!!! ...and go do something...

wrote in message
...
| I'm still playing with the rocket antenna.
| The rocket body is a 12 inch diameter aluminum tube.
|
| If I want to put a horzintal dipole on the body I can do one of two
| things.
|
|
| 1)Cut an Oval or oblong hole in the skin up near the electronics and
| then put in a fibnerglass panel, on that panel I put a cu foil dipole.
|
| How much bigger does the opening around the dipole have to be to not
| reduce the efficency of the antenna.
|
| 2)I can put a thin dialectric patch on the outside of the rocket and
| put the antenna on that.
| How thick would a fiberglass dielectric need to be for a good antenna?
|
|
|
| I now have a 900Mhz capable bird so I can trim the antenna for minimum
| SWR.
|
| This sunday is my last chance to make all of this work so I'm running
| out of time.
|
|
| Paul (Kl7JG)
|
|
|
|
|

wrote in :

I'm still playing with the rocket antenna.
The rocket body is a 12 inch diameter aluminum tube.

If I want to put a horzintal dipole on the body I can do one of two
things.


1)Cut an Oval or oblong hole in the skin up near the electronics and
then put in a fibnerglass panel, on that panel I put a cu foil dipole.

How much bigger does the opening around the dipole have to be to not
reduce the efficency of the antenna.

2)I can put a thin dialectric patch on the outside of the rocket and
put the antenna on that.
How thick would a fiberglass dielectric need to be for a good antenna?



I now have a 900Mhz capable bird so I can trim the antenna for minimum
SWR.

This sunday is my last chance to make all of this work so I'm running
out of time.


Paul (Kl7JG)

Did you consider a cylindrical patch around the body of the rocket?

Sam

Did you consider a cylindrical patch around the body of the rocket?


I've considered lots of things..
A cylindrical patch would probably be good,
but I lack the information to design one.


Paul

wrote in message
...
Did you consider a cylindrical patch around the body of the rocket?


I've considered lots of things..
A cylindrical patch would probably be good,
but I lack the information to design one.


Paul

Patch antenna design is described in "Antennas" by John D. Kraus, ISBN
0-07-035422-7, pp 745 - 749. If you do not have access to this book I can
scan and send you the pages.

A patch antenna consists of a conductive rectangle of dimension lambda/2 X
lambda, and mounted on a substrate over a ground plane. The longer
dimension is dependant on the Er of the substrate.

73,

Frank

wrote in message
...
I'm still playing with the rocket antenna.
The rocket body is a 12 inch diameter aluminum tube.



How high is the rocket going ? If you are running 1 watt of power, then
the rocket will be in view of the ground station ? then just about anything
you do will be good enough for a transmitting antenna. Try insulating
(electrically) the transmitter from the body of the rocket and feeding the
output of the transmitter directly to the body of the rocket.
Seems that you are over engineering a simple system.

A slot antenna obviates all the kludges your proposing.

wrote in message
...
I'm still playing with the rocket antenna.
The rocket body is a 12 inch diameter aluminum tube.

If I want to put a horzintal dipole on the body I can do one of two
things.


1)Cut an Oval or oblong hole in the skin up near the electronics and
then put in a fibnerglass panel, on that panel I put a cu foil dipole.

How much bigger does the opening around the dipole have to be to not
reduce the efficency of the antenna.

2)I can put a thin dialectric patch on the outside of the rocket and
put the antenna on that.
How thick would a fiberglass dielectric need to be for a good antenna?



I now have a 900Mhz capable bird so I can trim the antenna for minimum
SWR.

This sunday is my last chance to make all of this work so I'm running
out of time.


Paul (Kl7JG)

Paul wrote:
"The rocket body is a 12 inch diameter aluminum tube."

The tube could be slotted lengthwise and the gap insulated to make a
slot antenna. Low profile can minimize atmospheric drag.

Look at page 320 of Kraus` 3rd edition of "Antennas". On page 321 Kraus
writes:
"Typical slotted cylinder dimensions for resonance are D= 0.125 WL,
L=0.75 WL, and the slot width about 0.02 WL."

12 inches, the rocket tube diameter, is 30.48 cm. If this is 1/8 WL, the
WL= 2.438 m and F=123 MHz.

The length of the slot is 0.75x2.438=1.83 meters. Slot width is
0.02x2.438m=4.9 cm.

The length od the slotted cylinder is greater than 1/2-wavelength as
needed for resonance because the cylinder circumference is not an
infinite sheet.

Polarization is the same direction as the voltage across the slot,
horizontal when the cylinder is erect. It has been used as an
omnidirectional VHF broadcast antenna. The slotted cylinder can be
scaled for any frequency.

Best regards, Richard Harrison, KB5WZI