I am looking for some help developing a properly tuned piano wire
antenna for an all metal experimental rocket.
This particular vehicle currently uses a Digi International 9Xtream
100 mw transmitter which operates using Frequency Hopping Spread
Spectrum from 910 to 918 MHz.

The first flight used a .062" diameter length of piano wire cut so
that the exposed length was about 1/2 wavelength. The wire antenna was
isolated from the metal airfame with a small nylon penetrator and
connected to the transmitter via about a 12" length of RG-178 coax.
The coax was terminated at the antenna via two small jumpers (soldered
to the center conductor and shield). The shield was grounded on the
metal airframe transforming the entire rocket into an artificial
ground plane (the antenna was also swept back at about a 45 degree
angle to reduce drag.

During this first flight we observed a range of about 10 miles, about
half of the published range of this transmitter. The RF system is used
as a downlink for GPS data and we did not get a good radio link after
ignition until the rocket had descended to about 50,000 feet. Maximum
velocity was about Mach 3 which is why a conventional antenna cannot
be used as it will be melted by friction.

For the second version, we are thinking of using a slightly smaller
diameter piano wire for a 1/4 wave length antenna as I think this may
be more suitable for a system using an artificial ground plane. In
addition, I plan to terminate the RG-178 coax directly at the antenna
and seal it with potting compound. This new antenna will be mounted
totally on the exterior of the airframe and angled back only about 10
degrees to give a better radiation pattern.

However, I would really like to properly tune this new antenna and was
wondering if anyone in this group has any ideas as to how to do this.
Doing a tuned RCL circuit at this frequency is proving to be difficult
using discrete components, to say the least. I do not have an SWR, but
do have an RF millivolt meter as well as the means to measure the
capacitance between the antenna and metal airframe.

Any help will be appreciated as I would hate to fly this thing again
and not get it back because our RF downlink had insufficient range.

C. Newport

On Sat, 23 May 2009 16:40:22 -0700 (PDT), mr1956
wrote:

Maximum
velocity was about Mach 3 which is why a conventional antenna cannot
be used as it will be melted by friction.

Would seem to be at odds with:

This new antenna will be mounted
totally on the exterior of the airframe and angled back only about 10
degrees to give a better radiation pattern.

At Mach 3, I seriously doubt you could hold it as erect (80 degrees to
the fuselage) as you might try with smaller wire (in fact, I would say
it would be plastered down).

If your telemetry is directly below its ascendance, you might try a
full-wave or longer antenna trailing below (if it can withstand the
propulsion heat). If that is not possible, look into an inverted F:
http://www.qsl.net/kb7qhc/antenna/In...%20F/index.htm
(it doesn't have to be a thick antenna).

73's
Richard Clark, KB7QHC

On May 23, 11:08*pm, Richard Clark wrote:
On Sat, 23 May 2009 16:40:22 -0700 (PDT), mr1956
wrote:

Maximum
velocity was about Mach 3 which is why a conventional antenna cannot
be used as it will be melted by friction.

Would seem to be at odds with:

This new antenna will be mounted
totally on the exterior of the airframe and angled back only about 10
degrees to give a better radiation pattern.

At Mach 3, I seriously doubt you could hold it as erect (80 degrees to
the fuselage) as you might try with smaller wire (in fact, I would say
it would be plastered down).

If your telemetry is directly below its ascendance, you might try a
full-wave or longer antenna trailing below (if it can withstand the
propulsion heat). *If that is not possible, look into an inverted F:http://www.qsl.net/kb7qhc/antenna/In...%20F/index.htm
(it doesn't have to be a thick antenna).

73's
Richard Clark, KB7QHC

Yes the antenna will be pressed back against the airframe during
flight but should be erect at apogee and during descent. The previous
one survived just fine.

C. Newport

"mr1956" wrote in message
...
I am looking for some help developing a properly tuned piano wire
antenna for an all metal experimental rocket.
This particular vehicle currently uses a Digi International 9Xtream
100 mw transmitter which operates using Frequency Hopping Spread
Spectrum from 910 to 918 MHz.

The first flight used a .062" diameter length of piano wire cut so
that the exposed length was about 1/2 wavelength. The wire antenna was
isolated from the metal airfame with a small nylon penetrator and
connected to the transmitter via about a 12" length of RG-178 coax.
The coax was terminated at the antenna via two small jumpers (soldered
to the center conductor and shield). The shield was grounded on the
metal airframe transforming the entire rocket into an artificial
ground plane (the antenna was also swept back at about a 45 degree
angle to reduce drag.

During this first flight we observed a range of about 10 miles, about
half of the published range of this transmitter. The RF system is used
as a downlink for GPS data and we did not get a good radio link after
ignition until the rocket had descended to about 50,000 feet. Maximum
velocity was about Mach 3 which is why a conventional antenna cannot
be used as it will be melted by friction.

For the second version, we are thinking of using a slightly smaller
diameter piano wire for a 1/4 wave length antenna as I think this may
be more suitable for a system using an artificial ground plane. In
addition, I plan to terminate the RG-178 coax directly at the antenna
and seal it with potting compound. This new antenna will be mounted
totally on the exterior of the airframe and angled back only about 10
degrees to give a better radiation pattern.

However, I would really like to properly tune this new antenna and was
wondering if anyone in this group has any ideas as to how to do this.
Doing a tuned RCL circuit at this frequency is proving to be difficult
using discrete components, to say the least. I do not have an SWR, but
do have an RF millivolt meter as well as the means to measure the
capacitance between the antenna and metal airframe.

Any help will be appreciated as I would hate to fly this thing again
and not get it back because our RF downlink had insufficient range.

C. Newport

Hi C

Have you considered flush antennas, like slots?

Is is practical to use antenna directivity at the ground station to
increase the "range"?

It might be advantageous to use Linear Polarization on the rocket and
Circular Polarization on the ground.

For impedance measurement at L band, it is possible to build a slotted
line using plumbing supplies. That presumes that you already have access
to a signal generator and a detector to record the signal generator's
output.
A home built slotted line will have difficulty regestaring low VSWRs.
But, once it is known that the load impedance is close to the line impedance
(low VSWR), a directional coupler can be used to match more precisely.

I have built a "plumber's delight" slotted line that works well at 130
MHZ. The high quality directional couplers are affordable on eBay.
Note - If I can do it, it cant be too complicated!

Jerry KD6JDJ

On Sun, 24 May 2009 04:04:52 GMT, "Jerry"
wrote:

Have you considered flush antennas, like slots?

Slot antennas have the maximum lobe perpendicular to the rocket axis.
There's very little signal below the rocket. This is why tracking
stations are far away from the launch site. If the rocket were
overhead, and going straight up, there's no signal.

Slot antennas are also a power waste. You need 4 slots, run by a
power splitter, in order to insure that at least one antenna is
oriented in the direction of the receiver. Meanwhile, the other 3
slot antennas are radiating power to nobody in particular. Say goodby
to about 3/4th of your tx power. Receive sensitivity is not
affected.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"Jeff Liebermann" wrote in message
...
On Sun, 24 May 2009 04:04:52 GMT, "Jerry"
wrote:

Have you considered flush antennas, like slots?

Slot antennas have the maximum lobe perpendicular to the rocket axis.
There's very little signal below the rocket. This is why tracking
stations are far away from the launch site. If the rocket were
overhead, and going straight up, there's no signal.

Slot antennas are also a power waste. You need 4 slots, run by a
power splitter, in order to insure that at least one antenna is
oriented in the direction of the receiver. Meanwhile, the other 3
slot antennas are radiating power to nobody in particular. Say goodby
to about 3/4th of your tx power. Receive sensitivity is not
affected.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Hi Jeff

Why are you so negative?? I have designed and built lots of slot
antennas that were widely used on military aircraft. The efficiency is
quite good. I am sure a smart guy like you could design a slot antenna and
locate it for those guys with the 3G rocket. There hasnt been any text
that restricts where the slot could be located. As I read the original
post, they werent receiving signal from the accending rocket. Maybe they
only want to receive data that was recorded after the rocket reached it's
peak. There are lots of information that you and I dont yet know. But,
my major question for you is "Why are you so negative?".

Jerry KD6JDJ

On Sun, 24 May 2009 07:30:03 GMT, "Jerry"
wrote:


"Jeff Liebermann" wrote in message
.. .
On Sun, 24 May 2009 04:04:52 GMT, "Jerry"
wrote:

Have you considered flush antennas, like slots?

Slot antennas have the maximum lobe perpendicular to the rocket axis.
There's very little signal below the rocket. This is why tracking
stations are far away from the launch site. If the rocket were
overhead, and going straight up, there's no signal.

Slot antennas are also a power waste. You need 4 slots, run by a
power splitter, in order to insure that at least one antenna is
oriented in the direction of the receiver. Meanwhile, the other 3
slot antennas are radiating power to nobody in particular. Say goodby
to about 3/4th of your tx power. Receive sensitivity is not
affected.

Hi Jeff
Why are you so negative?? I have designed and built lots of slot
antennas that were widely used on military aircraft. The efficiency is
quite good. I am sure a smart guy like you could design a slot antenna and
locate it for those guys with the 3G rocket. There hasnt been any text
that restricts where the slot could be located. As I read the original
post, they werent receiving signal from the accending rocket. Maybe they
only want to receive data that was recorded after the rocket reached it's
peak. There are lots of information that you and I dont yet know. But,
my major question for you is "Why are you so negative?".
Jerry KD6JDJ

I don't think I'm being particularly negative or offensive. I offered
what I consider to be a more reasonable alternative (CP turnstile
antenna) and ran the path loss calculations to insure that it would
work. I also itemized why a slot antenna would be an inferior
solution. My main point is that with a vertically ascending rocket,
the antenna pattern should be primarily ahead and behind the rocket,
not perpendicular.

I've seen one paper design that used insulated fins for the 4
turnstile antenna elements. However, I haven't seen the actual
rocket. I also built a 2.4GHz antenna system for a model airplane for
a video downlink. The initial design was a slot antenna system in the
fuselage, which worked great when the aircraft was overhead, but did
badly when near the horizon and out of the antenna pattern. Two
vertical monopoles and a power splitter did much better, especially
since it worked well in inverted flight. I must admit that I haven't
designed a slot antenna system for a high power Mach 3 rocket. I did
build a small "G" motor rocket without telemetry but that doesn't
count for much.

Anyway, we're both guessing. Without a clue as to the size, geometry,
and construction of the rocket, the configuration of the ground
station antenna, the location of the ground station, and the
approximate trajectory (probably straight up), we can only speculate
as to the optimal design. My guess is that this a level 1 rocket with
an "H" or "I" motor which could barely tolerate the slight increase in
diameter required for multiple slot antnnas. Wire or fin antennas
don't add anything.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann wrote:
On Sun, 24 May 2009 04:04:52 GMT, "Jerry"
wrote:

Have you considered flush antennas, like slots?

Slot antennas have the maximum lobe perpendicular to the rocket axis.
There's very little signal below the rocket. This is why tracking
stations are far away from the launch site. If the rocket were
overhead, and going straight up, there's no signal.

That was my first thought on side mounted antennas.

The best solution would be something on the fins if that were
possible with the airframe design.


--
Jim Pennino

Remove .spam.sux to reply.

On May 24, 12:04*am, "Jerry" wrote:
"mr1956" wrote in message

...



I am looking for some help developing a properly tuned piano wire
antenna for an all metal experimental rocket.
This particular vehicle currently uses a Digi International 9Xtream
100 mw transmitter which operates using Frequency Hopping Spread
Spectrum from 910 to 918 MHz.

The first flight used a .062" diameter length of piano wire cut so
that the exposed length was about 1/2 wavelength. The wire antenna was
isolated from the metal airfame with a small nylon penetrator and
connected to the transmitter via about a 12" length of RG-178 coax.
The coax was terminated at the antenna via two small jumpers (soldered
to the center conductor and shield). *The shield was grounded on the
metal airframe transforming the entire rocket into an artificial
ground plane (the antenna was also swept back at about a 45 degree
angle to reduce drag.

During this first flight we observed a range of about 10 miles, about
half of the published range of this transmitter. The RF system is used
as a downlink for GPS data and we did not get a good radio link after
ignition until the rocket had descended to about 50,000 feet. *Maximum
velocity was about Mach 3 which is why a conventional antenna cannot
be used as it will be melted by friction.

For the second version, we are thinking of using a slightly smaller
diameter piano wire for a 1/4 wave length antenna as I think this may
be more suitable for a system using an artificial ground plane. *In
addition, I plan to terminate the RG-178 coax directly at the antenna
and seal it with potting compound. This new antenna will be mounted
totally on the exterior of the airframe and angled back only about 10
degrees to give a better radiation pattern.

However, I would really like to properly tune this new antenna and was
wondering if anyone in this group has any ideas as to how to do this.
Doing a tuned RCL circuit at this frequency is proving to be difficult
using discrete components, to say the least. I do not have an SWR, but
do have an RF millivolt meter as well as the means to measure the
capacitance between the antenna and metal airframe.

Any help will be appreciated as I would hate to fly this thing again
and not get it back because our RF downlink had insufficient range.

C. Newport

* Hi C

* Have you considered flush antennas, like slots?

* Is is practical to use antenna directivity at the ground station to
increase the "range"?

* It might be advantageous to use Linear Polarization on the rocket and
Circular Polarization on the ground.

* For impedance measurement at L band, it is possible to build a slotted
line using plumbing supplies. * That presumes that you already have access
to a signal generator and a detector to record the signal generator's
output.
* A home built slotted line will have difficulty regestaring low VSWRs.
But, once it is known that the load impedance is close to the line impedance
(low VSWR), a directional coupler can be used to match more precisely.

* I have built a "plumber's delight" slotted line that works well at 130
MHZ. * The high quality directional couplers are affordable on eBay.
* Note - If I can do it, it cant be too complicated!

* * * * * * * * * * * * Jerry * KD6JDJ
I have looked at slotted or flush wrap around antennas but integrating
one into the existing design would be difficult due to the wall
thickness of the metal. Something like that would have to be mounted
flush and I would be worried about the wind blast peeling the thing
off. Certainly, there is much that can be done but I am unfortunately
not Wallops Island and have limited resources like anyone else.

"mr1956" wrote in message
...
On May 24, 12:04 am, "Jerry" wrote:
"mr1956" wrote in message

...



I am looking for some help developing a properly tuned piano wire
antenna for an all metal experimental rocket.
This particular vehicle currently uses a Digi International 9Xtream
100 mw transmitter which operates using Frequency Hopping Spread
Spectrum from 910 to 918 MHz.

The first flight used a .062" diameter length of piano wire cut so
that the exposed length was about 1/2 wavelength. The wire antenna was
isolated from the metal airfame with a small nylon penetrator and
connected to the transmitter via about a 12" length of RG-178 coax.
The coax was terminated at the antenna via two small jumpers (soldered
to the center conductor and shield). The shield was grounded on the
metal airframe transforming the entire rocket into an artificial
ground plane (the antenna was also swept back at about a 45 degree
angle to reduce drag.

During this first flight we observed a range of about 10 miles, about
half of the published range of this transmitter. The RF system is used
as a downlink for GPS data and we did not get a good radio link after
ignition until the rocket had descended to about 50,000 feet. Maximum
velocity was about Mach 3 which is why a conventional antenna cannot
be used as it will be melted by friction.

For the second version, we are thinking of using a slightly smaller
diameter piano wire for a 1/4 wave length antenna as I think this may
be more suitable for a system using an artificial ground plane. In
addition, I plan to terminate the RG-178 coax directly at the antenna
and seal it with potting compound. This new antenna will be mounted
totally on the exterior of the airframe and angled back only about 10
degrees to give a better radiation pattern.

However, I would really like to properly tune this new antenna and was
wondering if anyone in this group has any ideas as to how to do this.
Doing a tuned RCL circuit at this frequency is proving to be difficult
using discrete components, to say the least. I do not have an SWR, but
do have an RF millivolt meter as well as the means to measure the
capacitance between the antenna and metal airframe.

Any help will be appreciated as I would hate to fly this thing again
and not get it back because our RF downlink had insufficient range.

C. Newport

Hi C

Have you considered flush antennas, like slots?

Is is practical to use antenna directivity at the ground station to
increase the "range"?

It might be advantageous to use Linear Polarization on the rocket and
Circular Polarization on the ground.

For impedance measurement at L band, it is possible to build a slotted
line using plumbing supplies. That presumes that you already have access
to a signal generator and a detector to record the signal generator's
output.
A home built slotted line will have difficulty regestaring low VSWRs.
But, once it is known that the load impedance is close to the line
impedance
(low VSWR), a directional coupler can be used to match more precisely.

I have built a "plumber's delight" slotted line that works well at 130
MHZ. The high quality directional couplers are affordable on eBay.
Note - If I can do it, it cant be too complicated!

Jerry KD6JDJ
I have looked at slotted or flush wrap around antennas but integrating
one into the existing design would be difficult due to the wall
thickness of the metal. Something like that would have to be mounted
flush and I would be worried about the wind blast peeling the thing
off. Certainly, there is much that can be done but I am unfortunately
not Wallops Island and have limited resources like anyone else.


Hi C

It looks like your "wire" antenna might actually be OK for your project.
You have demonstrated that it works when the rocket is nearly 10 miles away
when you hoped for 20 miles. Evidently, the antenna doesnt need to
function while the rocket is accending.
Are you able to improve the ground based antenna The equipment you now
have would need only 6 dB improvement to provide the 20 mile range.
I'd like to know more about your ground based antenna system.

Jerry KD6JDJ (who has lots of small
diameterTeflon dielectric coax to donate to a real project)