wireless range vs. power

Hi,

I've ordered a wireless webcam that will be out onboard an autonomous
aircraft for a university project.

The camera has a "2dBi Diversity Antenna" and transmits video over an
IP protocol in the 2.4-2.4835 GHz range.

Now the aircraft needs to operate in a 500x500m area, although I
expect that my ground station computer will be placed some distance
away from the operating area.

My problem is that I don't know how to calculate the achievable
transmission range from power and frequency. Is there a rule of thumb
calculation for finding the transmission range?

UK regulations say that I cant have a power above 100mW- does anybody
know what range is achievable with this power in the 2.4 GHz band?

Any help is heartfuly appreciated.

Adam

Adam Chapman wrote:
> My problem is that I don't know how to calculate the achievable
> transmission range from power and frequency. Is there a rule of thumb
> calculation for finding the transmission range?

There are too many unpredictable variables. If your airplane tilts in
just the slightest, you'll loose the signal. All you can really do is
try it out and see how far it works.

On Apr 2, 4:37*pm, DTC <m...@nothingtoseehere.zzx> wrote:
> Adam Chapman wrote:
> > My problem is that I don't know how to calculate the achievable
> > transmission range from power and frequency. Is there a rule of thumb
> > calculation for finding the transmission range?
>
> There are too many unpredictable variables. If your airplane tilts in
> just the slightest, you'll loose the signal. All you can really do is
> try it out and see how far it works.

even if i have an omni-directional antenna?

Adam Chapman wrote:
> Hi,
>
> I've ordered a wireless webcam that will be out onboard an autonomous
> aircraft for a university project.
>
> The camera has a "2dBi Diversity Antenna" and transmits video over an
> IP protocol in the 2.4-2.4835 GHz range.
>
> Now the aircraft needs to operate in a 500x500m area, although I
> expect that my ground station computer will be placed some distance
> away from the operating area.
>
> My problem is that I don't know how to calculate the achievable
> transmission range from power and frequency. Is there a rule of thumb
> calculation for finding the transmission range?

Communication is a 2 way operation and you would need to know the Rx
sensitivity, Tx o/p, Antenna gain... of both the devices to get even a
vague idea of the Link distance that would be achieved by 2 staic devices.
If one of the devices is moving in 3 dimensions that would make it
extremely difficult to calculate. You say it would operate in an area
500x500 metres...not true as it would be 500x500xheight metres.
If you were
>
> UK regulations say that I cant have a power above 100mW- does anybody
> know what range is achievable with this power in the 2.4 GHz band?
>
> Any help is heartfuly appreciated.
>
> Adam

LR wrote:
> Adam Chapman wrote:
>> Hi,
>>
>> I've ordered a wireless webcam that will be out onboard an autonomous
>> aircraft for a university project.
>>
>> The camera has a "2dBi Diversity Antenna" and transmits video over an
>> IP protocol in the 2.4-2.4835 GHz range.
>>
>> Now the aircraft needs to operate in a 500x500m area, although I
>> expect that my ground station computer will be placed some distance
>> away from the operating area.
>>
>> My problem is that I don't know how to calculate the achievable
>> transmission range from power and frequency. Is there a rule of thumb
>> calculation for finding the transmission range?
>
> Communication is a 2 way operation and you would need to know the Rx
> sensitivity, Tx o/p, Antenna gain... of both the devices to get even a
> vague idea of the Link distance that would be achieved by 2 staic devices.
> If one of the devices is moving in 3 dimensions that would make it
> extremely difficult to calculate. You say it would operate in an area
> 500x500 metres...not true as it would be 500x500xheight metres.

Bleeding cats..grrh.
How do you intend to keep the Antennas in the same plane.Depending on
the gain of the omni on the ground unit you may find that if your
aircraft goes to high the camera's antenna may not be in the beamwidth
of the groundstaions antenna.
http://my.athenet.net/~multiplx/cgi-bin/omni.main.cgi

You could perhaps get a rough idea of the max distance of a static link
using a link calculator:-
http://www.wifiextreme.com.au/index....in_page=page_5
However adding movement in will just just reduce the workable distance.
You will also have to try and factor in the Data transfer rate you need
to use for an acceptable video quality. The higher the rate the less
distance.

>>
>> UK regulations say that I cant have a power above 100mW- does anybody
>> know what range is achievable with this power in the 2.4 GHz band?
>>
>> Any help is heartfuly appreciated.
>>
>> Adam

Adam Chapman wrote:
> On Apr 2, 4:37 pm, DTC <m...@nothingtoseehere.zzx> wrote:
>> Adam Chapman wrote:
>>> My problem is that I don't know how to calculate the achievable
>>> transmission range from power and frequency. Is there a rule of
>>> thumb calculation for finding the transmission range?
>>
>> There are too many unpredictable variables. If your airplane tilts in
>> just the slightest, you'll loose the signal. All you can really do is
>> try it out and see how far it works.
>
> even if i have an omni-directional antenna?

remember that any omni antenna readiates as a donut sitting over the
antenna.
So - just as an example - imagine if the plane was directly overhead,
you might be able to see it, but not receive the video since your receiving
"donut"
and the plane's transmitting "donut" would not intersect.

As you can see - the name of the game is for both plane + ground station
to have intersecting donuts....
As the plane flies away, you may actually receive a better signal
as the donut beamwidth pattern increases with distance - but strength
decreases -
SO - ??

On Wed, 2 Apr 2008 08:00:06 -0700 (PDT), Adam Chapman
<adam.chapman@student.manchester.ac.uk> wrote:

>I've ordered a wireless webcam that will be out onboard an autonomous
>aircraft for a university project.

I've done that. You're about to have a battery problem.

>The camera has a "2dBi Diversity Antenna" and transmits video over an
>IP protocol in the 2.4-2.4835 GHz range.

Duz this camera have a manufacturer and a model number? A URL with
the specifications would be nice.

2dBi is a simple monopole antenna. It has a radiation pattern that
looks like a donut. There's a big null when in line with the antenna,
such as when the aircraft is flying directly overhead.

>Now the aircraft needs to operate in a 500x500m area, although I
>expect that my ground station computer will be placed some distance
>away from the operating area.

I have this thing about numbers. How far is "some distance"? How
high does the air thing have to fly? What's the MAXIMUM distance you
expect to see an image?

>My problem is that I don't know how to calculate the achievable
>transmission range from power and frequency.

Neither do I. You've supplied exactly one non-ambiguous number (the
2dBi antenna gain). What's missing is everything else that's on the
specification sheet.

>Is there a rule of thumb
>calculation for finding the transmission range?

If you can see your thumb, you can communicate.

Yes, there are calculations possible. They're actually fairly easy.
See example at:
<http://wireless.wikia.com/wiki/Wi-Fi#Link_Calculations>
However, you're doing video which requires some tweaks to the
calculations (depending on bandwidth and modulation method). I can't
help without you supplying some numbers.

>UK regulations say that I cant have a power above 100mW- does anybody
>know what range is achievable with this power in the 2.4 GHz band?

Sorry, no answer without knowing the antenna gains, receiver
sensitivity, SNR required, and modulation method.

>Any help is heartfuly appreciated.

Take your video xmitter and receiver and connect to a portable TV.
Start walking. When the picture starts to look horrible, stop. Record
the distance. Let's say it's 100 meters.

If you increase the antenna gain by 6dB, you will get twice the range
or 200 meters. 12dB increase in gain will give you 4 times the range,
or 400 meters. 18dB gain will yield 8 times the range. Ad nasusium.
The problem is that every time you increase the gain, the beamwidth
and pattern of the antenna gets narrower and narrower. The airplane
mounted video camera I helped throw together had about a 1000 meter
range. However, we used a 24dBi dish antenna on the ground, that
tracked the aircraft (both automagically and manually).

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

On Wed, 02 Apr 2008 15:37:48 GMT, DTC <me@nothingtoseehere.zzx> wrote:

>If your airplane tilts in
>just the slightest, you'll loose the signal.

Nope. A 2dBi donut pattern isn't the same as a hemispherical pattern,
but close enough. When we were tinkering with model airplane video,
the best antenna was a 3cm coaxial antenna (1/4 wave driven element,
1/4 wave coax sleeve) made out of a piece of RG-175, dangling roughly
downward. The only times when the signal disappeared were when the
plane flew overhead and when the body blocked the signal (i.e.
inverted flying). The null was rather sharp and the image returned
quickly. It's not as bad as it would seem. Some of the other model
airplane pilots were using patch antenna, which had less drag, and
were only useful in level flight.

What was really cool was flying the plane with the camera in the
cockpit and watching through video goggles. 640x480 for each eye:
<http://www.vuzix.com/iwear/products_vr920.html>
Nice for watching 3D TV when not flying. Say goodby to about $350 for
those.

Incidentally, almost all the ground based video receivers had some
manner of directional antenna attached. Ours was overkill with a
24dBi dish (because I had one handy). Others were using everything
from cantennas to big panels. There were a few high gain omnis, but
they didn't work too well.

>All you can really do is
>try it out and see how far it works.

Yep. I kinda prefer calculations first, but a sanity check is always
a good idea.

Thought 2.4GHz was kinda crowded? Futaba 2.4GHz radio control.
<http://2.4gigahertz.com/>
The wireless video and these should interfere nicely.

Ugh. Back to working on my taxes...


--
Jeff Liebermann jeffl@cruzio.com
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:

<snip>

> The airplane mounted video camera I helped throw together had about
> a 1000 meter range. However, we used a 24dBi dish antenna on the
> ground, that tracked the aircraft (both automagically and manually).

Did you build a nutating feed for the ground station, or perhaps a
phased array with electronic nutation?

Michael

On Wed, 02 Apr 2008 20:33:34 -0600, msg <msg@_cybertheque.org_> wrote:

>Jeff Liebermann wrote:
>
><snip>
>
>> The airplane mounted video camera I helped throw together had about
>> a 1000 meter range. However, we used a 24dBi dish antenna on the
>> ground, that tracked the aircraft (both automagically and manually).

>Did you build a nutating feed for the ground station, or perhaps a
>phased array with electronic nutation?
>Michael

Nope. There were numerous models of tracking antenna. That was my
job. The problem was that the spread spectrum signal does not have a
carrier, which made it difficult to throw together an easy tracking
circuit. The ability of the airplane to fly close and perpendicular
to the antenna made tracking even more difficult. Worse, the 24dBi
dish has a -3dB beamwidth of about 7 degrees. What seemed like an
easy project turned into a real mess.

One scheme that came really close to working required 4 additional
receivers. The center feed mount was extended beyond the feed and
made from an RF absorber (i.e. PVC pipe fill of water). 4 antennas
were arranged in 4 quadrants on each side of the center feed pipe
extension. With the signal source dead ahead, the signal levels at
all 4 receivers is (allegedly) identical. If the antenna were offset
in one direction, the center pipe casts an RF "shadow" on the one of
the 4 antennas. A differential amplifier runs a gimbal mounted pair
of motors to correct the direction.

This worked well fairly for tracking under ideal conditions, but had
acquisition problems that drove me into overtime and later panic.
There were just too many reflections that screwed up the direction. If
I had a deep solid dish (large f/D ratio), instead of a barbeque grill
dish, the reflections would have been minimized and it might have
worked better. However, once the direction antennas were hit by a
reflection, the motor would swerve the antenna radically, losing lock,
and not easily recovering.

The radio link was via 802.11b wi-fi so unlike the ATV link, there was
a transmitter involved at the dish. When it transmitted, the
directional receivers were instantly overloaded. I worked around this
problem by temporarily disabling the servos in transmit.

I eventually gave up on the RF approach.

There were several other attempts to build a tracker. I finally threw
together an optical system that worked. It was similar to the RF
tracker, but was immune to all but the most disgusting reflections.
The aircraft carried several green LED's that pulsed at about 100 Hz.
The 4 antennas were replaced by 4 security camera lenses and photo
transistors. The center pipe was replaced by a fiberglass tube, which
blocks light, but passes RF.

This system worked much better, especially at night. It crapped out
when pointed into the sun, when some dingbat shines his flashlight on
the antenna, and when I took a flash photo. Range was limited to
about 300 meters. I never did nail down the servo loop damping
factor, so it tended to either crawl across the traverse, or twitch
badly as it moved. Neither seemed to bother the RF data link, but it
sure made everyone around the antenna nervous. Like the RF solution,
it worked for tracking and sucked for acquisition.

I had thought of using a nutating (conical scan) feed (straight out of
the WWII SCR-584 radar):
<http://www.carnarvonspace.com/wiki/index.php?title=SCR-584_Technical_Description>
However, I didn't have time to machine the required components and the
corresponding control system. When I was much younger, there were
tons of those feeds available in the WWII surplus stores, but those
are long gone today.

I have some other ideas on how to do a wi-fi tracking antenna.
However, I keep seeing high skool and college project proposals that
involve the construction of such systems. I don't wanna ruin it for
the students.


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

Thanks to all of you, I replied to this particular post because it had
the most questions for me to answer.
I do hope that Im not appearing to be lazy here, I've never had to
work in wireless systems as I am an aerodynamisist recently turned
image processing geek. I was expecting my question to have an easy
answer but as usual here wasn't so sorry and thank you for taking your
own time to help me.

On Apr 2, 11:54 pm, Jeff Liebermann <je...@cruzio.com> wrote:
> On Wed, 2 Apr 2008 08:00:06 -0700 (PDT), Adam Chapman
>
> <adam.chap...@student.manchester.ac.uk> wrote:
> >I've ordered a wireless webcam that will be out onboard an autonomous
> >aircraft for a university project.
>
> I've done that. You're about to have a battery problem.
>
> >The camera has a "2dBi Diversity Antenna" and transmits video over an
> >IP protocol in the 2.4-2.4835 GHz range.
>
> Duz this camera have a manufacturer and a model number? A URL with
> the specifications would be nice.
>

The camera is a Trendnet IP-TV301W model, specification at
http://trendnet.com/products/proddet...-IP301W&cat=48.
I don't physically have the camera yet because the university is still
processing the account, which in my experience can take a very long
time. If it is possible to estimate transmission ranges with certain
equipment, I would have an easier job justifying the expense to my
department.

> 2dBi is a simple monopole antenna. It has a radiation pattern that
> looks like a donut. There's a big null when in line with the antenna,
> such as when the aircraft is flying directly overhead.
>

The 2dBi antenna can be replaced, if there is a better type then I am
happy to use it. I would prefer an antenna that emits as spherical a
pattern as possible, otherwise we will have to limit aircraft
maneuevres.



> >Now the aircraft needs to operate in a 500x500m area, although I
> >expect that my ground station computer will be placed some distance
> >away from the operating area.
>
> I have this thing about numbers. How far is "some distance"? How
> high does the air thing have to fly? What's the MAXIMUM distance you
> expect to see an image?
>

I have just recieved more information from the competition organisers,
who tell me that all flying will be within 500m of the launch site and
flying is not permitted above 400ft (121.92 m) This gives the max.
Euclidean distance as 514.65m, although i expect we will be measuring
that distance on the aircraft with GPS, and with the civilian accuracy
limitations on GPS (~ +- 12m), I would suggest a target transmission
distance of 550m.

Due to safety rules we will never lose sight of the aircraft so we can
expect no obstacles between transmitter and reciever.

I've been slowly writing this reply all day, and thinking a lot as i
do so. A helical antenna looks the best as it is the most isotropic,
although it is also pretty big for our aircraft. However even that has
+-45 degree 3dB lobe, so i might have to have the aircraft bank more
when closer to the centre of its circular mission area.

The link calculator link from LR told me that if i put an antenna with
a 7dBi gain (like the one at _) on the UAV and at the ground station,
i will have a range of over 7km with a 100mW transmitter, which I
assume can be achieved using an in-line amplifier. Does this
calculator use the range in the direction of the strongest energy
emisiion from the antenna?

I guess that more than on antenna on the same aircraft with different
orientations would interfere with each others signals?

Adam

Thanks to all of you, I replied to this particular post because it had
the most questions for me to answer.
I do hope that Im not appearing to be lazy here, I've never had to
work in wireless systems as I am an aerodynamisist recently turned
image processing geek. I was expecting my question to have an easy
answer but as usual here wasn't so sorry and thank you for taking your
own time to help me.

On Apr 2, 11:54 pm, Jeff Liebermann <je...@cruzio.com> wrote:
> On Wed, 2 Apr 2008 08:00:06 -0700 (PDT), Adam Chapman
>
> <adam.chap...@student.manchester.ac.uk> wrote:
> >I've ordered a wireless webcam that will be out onboard an autonomous
> >aircraft for a university project.
>
> I've done that. You're about to have a battery problem.
>
> >The camera has a "2dBi Diversity Antenna" and transmits video over an
> >IP protocol in the 2.4-2.4835 GHz range.
>
> Duz this camera have a manufacturer and a model number? A URL with
> the specifications would be nice.
>

The camera is a Trendnet IP-TV301W model, specification at
http://trendnet.com/products/proddet...-IP301W&cat=48.
I don't physically have the camera yet because the university is still
processing the account, which in my experience can take a very long
time. If it is possible to estimate transmission ranges with certain
equipment, I would have an easier job justifying the expense to my
department.

> 2dBi is a simple monopole antenna. It has a radiation pattern that
> looks like a donut. There's a big null when in line with the antenna,
> such as when the aircraft is flying directly overhead.
>

The 2dBi antenna can be replaced, if there is a better type then I am
happy to use it. I would prefer an antenna that emits as spherical a
pattern as possible, otherwise we will have to limit aircraft
maneuevres.



> >Now the aircraft needs to operate in a 500x500m area, although I
> >expect that my ground station computer will be placed some distance
> >away from the operating area.
>
> I have this thing about numbers. How far is "some distance"? How
> high does the air thing have to fly? What's the MAXIMUM distance you
> expect to see an image?
>

I have just recieved more information from the competition organisers,
who tell me that all flying will be within 500m of the launch site and
flying is not permitted above 400ft (121.92 m) This gives the max.
Euclidean distance as 514.65m, although i expect we will be measuring
that distance on the aircraft with GPS, and with the civilian accuracy
limitations on GPS (~ +- 12m), I would suggest a target transmission
distance of 550m.

Due to safety rules we will never lose sight of the aircraft so we can
expect no obstacles between transmitter and reciever.

I've been slowly writing this reply all day, and thinking a lot as i
do so. A helical antenna looks the best as it is the most isotropic,
although it is also pretty big for our aircraft. However even that has
+-45 degree 3dB lobe, so i might have to have the aircraft bank more
when closer to the centre of its circular mission area.

The link calculator link from LR told me that if i put an antenna with
a 7dBi gain (like the one at _) on the UAV and at the ground station,
i will have a range of over 7km with a 100mW transmitter, which I
assume can be achieved using an in-line amplifier. Does this
calculator use the range in the direction of the strongest energy
emisiion from the antenna?

I guess that more than on antenna on the same aircraft with different
orientations would interfere with each others signals?

Adam

Adam Chapman wrote:

> A helical antenna looks the best as it is the most isotropic,
> although it is also pretty big for our aircraft. However even that has
> +-45 degree 3dB lobe, so i might have to have the aircraft bank more
> when closer to the centre of its circular mission area.

How about taking a lesson from radiosonde antennas; I don't know about
current models, but for a very long time the antenna at 1680 MHz was
a 1/4 wave stub mounted at the center of an inverted conical reflector
(about 60 degrees). When suspended from the balloon, the antenna points
downward and illuminates the ground with a pattern formed from that
of the stub combined with the reflector, giving horizon-wide coverage
with no nulls for high inclination either.

Also, you could mount two such antennas on the fuselage, at 180 degrees
top and bottom and use a splitter to drive them so that there is
coverage during maneuvers.

Michael

Jeff Liebermann wrote:

<snip>

Sounds like a heck of a project you did ;)

>
> I had thought of using a nutating (conical scan) feed (straight out of
> the WWII SCR-584 radar):
> <http://www.carnarvonspace.com/wiki/index.php?title=SCR-584_Technical_Description>
> However, I didn't have time to machine the required components and the
> corresponding control system. When I was much younger, there were
> tons of those feeds available in the WWII surplus stores, but those
> are long gone today.

In days gone by, I had feeds from the MPQ-10A mortar tracking radar as well
as the GMD-1 ground station.

Michael

On Thu, 3 Apr 2008 08:12:00 -0700 (PDT), Adam Chapman
<adam.chapman@student.manchester.ac.uk> wrote:

>I do hope that Im not appearing to be lazy here, I've never had to
>work in wireless systems as I am an aerodynamisist recently turned
>image processing geek.

If this is a skool project, you are expected to do your own research
and calculations. You don't learn much by having us doing it for you.
If you have a *SPECIFIC* problem with some aspect of the project, feel
free to ask. However, the basic design in implimentation should be
all your work.

>I was expecting my question to have an easy
>answer but as usual here wasn't so sorry and thank you for taking your
>own time to help me.

Welcome to engineering at its worst. The URL I listed:
<http://wireless.wikia.com/wiki/Wi-Fi#Link_Calculations>
shows a simplified wireless link calculation. You are apparently
using 802.11b/g instead of VSB modulation for video (and data) so the
examples should work. Use this as the basis for your calcs. However,
please note that the resultant numbers are the *BEST* case
calculations. Real world situations only make things worse. For
example, the 2dBi gain of the antenna is actually the MAXIMUM gain of
the antenna. If you are off axis from the antenna pattern, the gain
(and range) will be less. Receiver sensitivity is never as good as
they claim. This should help:
<http://802.11junk.com/jeffl/rx-sens/receiver%20sensitivity.htm>
You will need to specify the other end of your radio link (equipment,
coax, antenna) before I can help with the numbers. It's really quite
simple.

>The camera is a Trendnet IP-TV301W model, specification at
>http://trendnet.com/products/proddet...-IP301W&cat=48.

OK. 802.11b/g. Draws 7 watts (at 12V) and weighs 0.5kg. Do you
have any idea of how big a battery will need to be to supply 7 watts
of continuous power? 4ea LIPO cell phone batteries will do the trick,
but you'll only have perhaps 15 minutes of operating time. To lift
all this, the plane doesn't need to be huge, but it certainly won't be
a styrofoam fly weight.

>I don't physically have the camera yet because the university is still
>processing the account, which in my experience can take a very long
>time.

The local university owes me some money from a project that is now 22
years overdue. Good luck.

>If it is possible to estimate transmission ranges with certain
>equipment, I would have an easier job justifying the expense to my
>department.

I don't see the connection between range and funding. I suspect
you'll do better with a feasability and finance study, than with a
performance estimate.

>The 2dBi antenna can be replaced, if there is a better type then I am
>happy to use it. I would prefer an antenna that emits as spherical a
>pattern as possible, otherwise we will have to limit aircraft
>maneuevres.

It really depends on what material you make the airplane from. If RF
transparent, a simple monopole (as supplied) will work. When
inverted, the signal will go through the aircraft. However, if you
make the airplane from reflective or absorptive materials, you'll need
multiple antennas. One 1/4 wave monopole on top and one on the bottom
should be sufficient. With a small ground plane under the antenna,
the pattern should be mostly cardioid shaped. If you have a wind
resistance problem, you can use a small ceramic patch antenna instead.
It is possible to model the antenna pattern using (free) antenna
modeling tools:
<http://home.ict.nl/~arivoors/>
The sample files include a 747 aircraft (which will need to be
scaled). This is not exactly a trivial exercise, a potential time
burning diversion, and is probably overkill for what you're
attempting. It's easy enough to construct a model, install the
camera, and just play with the position of the antenna until it's a
workable compromise.

Note that installing a bigger antenna on the airplane is not what you
want. Bigger antennas imply more gain. You want hemispherical
antenna pattern which requires a smaller or simpler antenna. Here's
an approximation of an isotropic antenna:
<http://802.11junk.com/jeffl/antennas/isotropic/index.html>
I think this is overkill and probably not practical on an airplane. If
you're going to do work with the antenna, do it on the ground station.

>I have just recieved more information from the competition organisers,
>who tell me that all flying will be within 500m of the launch site and
>flying is not permitted above 400ft (121.92 m) This gives the max.
>Euclidean distance as 514.65m, although i expect we will be measuring
>that distance on the aircraft with GPS, and with the civilian accuracy
>limitations on GPS (~ +- 12m), I would suggest a target transmission
>distance of 550m.
>
>Due to safety rules we will never lose sight of the aircraft so we can
>expect no obstacles between transmitter and reciever.

If this is competition flying, it's also likely (but not guaranteed)
that you'll also get minimal 2.4GHz interference. It's traditional to
confiscate the controllers during the competition to prevent sabotage.
That works because RC has dedicated frequencies. That's NOT the case
with 2.4GHz, where there's a chance that some lunatic, with a portable
wireless router, can crash your flying machine. You can also lose
control when the aircraft flys over a coffee shop wireless hot spot.
(I'm assuming that you'll be controlling on 2.4GHz). I sure hope this
is going to be run in the middle of nowhere. Testing it at skool,
where there's lots of 2.4GHz interference, is going to be ummm...
interesting.

>I've been slowly writing this reply all day, and thinking a lot as i
>do so.

At the beginning of any project, leaps of faith, wild ideas, the
shooting from the hip, are standard procedure. Once the ideas are
ossified, then you can be more studious and careful.

>A helical antenna looks the best as it is the most isotropic,

Too big, too much drag, too critical, poor gain to volume ratio. If
you're going to go to that level of complexity, think about two
ceramic patch antennas with a -3dB Wilkinson combiner. Two back to
back cartoid patterns equal roughly a hemisphere.

>although it is also pretty big for our aircraft. However even that has
>+-45 degree 3dB lobe, so i might have to have the aircraft bank more
>when closer to the centre of its circular mission area.

Translation. If you have a hole in the antenna pattern, you're going
to lose control. A helix also has no gain in the reverse direction,
so you'll need two. Hint: Look at what's on a real airplane or
guided missile.

>The link calculator link from LR told me that if i put an antenna with
>a 7dBi gain (like the one at _) on the UAV and at the ground station,
>i will have a range of over 7km with a 100mW transmitter, which I
>assume can be achieved using an in-line amplifier. Does this
>calculator use the range in the direction of the strongest energy
>emisiion from the antenna?

I'm still missing some numbers. See the example calcs on the URL I
mentioned. Copy the table of numbers and plug in YOUR numbers.
Remember, those are the BEST case calculations. Reality only makes it
worse.

>I guess that more than on antenna on the same aircraft with different
>orientations would interfere with each others signals?

If the two antennas cannot "see" each other, they will not mangle the
combined pattern. What other signals?

Good luck. Sounds like an interesting project. Watch your weight and
power consumption.
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Thu, 03 Apr 2008 10:41:08 -0600, msg <msg@_cybertheque.org_> wrote:

>Adam Chapman wrote:
>
>> A helical antenna looks the best as it is the most isotropic,
>> although it is also pretty big for our aircraft. However even that has
>> +-45 degree 3dB lobe, so i might have to have the aircraft bank more
>> when closer to the centre of its circular mission area.
>
>How about taking a lesson from radiosonde antennas; I don't know about
>current models, but for a very long time the antenna at 1680 MHz was
>a 1/4 wave stub mounted at the center of an inverted conical reflector
>(about 60 degrees). When suspended from the balloon, the antenna points
>downward and illuminates the ground with a pattern formed from that
>of the stub combined with the reflector, giving horizon-wide coverage
>with no nulls for high inclination either.

Radiosondes have two basic assumptions. The transmitter is always
above the receiver and that antenna is always roughly vertically
oriented. Those assumptions don't work well with an RC airplane,
which can easily be inverted, at odd angles, and at the same elevation
as the controller. Incidentally, the usual RC screwup is losing
control on landing, where the ground (small hills, cars, buildings)
block the signal and the radio link loses control.

>Also, you could mount two such antennas on the fuselage, at 180 degrees
>top and bottom and use a splitter to drive them so that there is
>coverage during maneuvers.

Yep. That's what I'm thinking. Two cardioid patch antennas make a
fair hemispherical pattern. The receive sensitivity won't be affected
much by the splitter, but the xmit power will be equally divided
between the two antennas. Link calcs in each direction will need to
be independently calculated.

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

On Thu, 03 Apr 2008 10:43:07 -0600, msg <msg@_cybertheque.org_> wrote:

>Jeff Liebermann wrote:
>
><snip>
>
>Sounds like a heck of a project you did ;)

Not "my" project. I originally got involved in bailing out a group of
arrogant engineers by cleaning up the antenna design. That grew
rapidly into cleaning up the control system, data link, and tracking
mechanism. The basic design was already done when I arrived. I just
made it all work.

One of the bad habits found in engineering is stopping when there is a
problem. These guys were running in circles around the problems
without actually attacking the problem. One had spent about a month
doing a computer simulation of a fundamentally flawed control system.
So, I got to jump in with both feet, turn the muddy waters into
quicksand, and kick those involved into action. Once the sacred cows
were slaughtered and sacrificed, and those involved were willing to
question their own assumptions, progress was rapid. I wasn't the only
one spending sleepless nights on this project.

>In days gone by, I had feeds from the MPQ-10A mortar tracking radar as well
>as the GMD-1 ground station.

2.7GHz, as I recall. Nice:
<http://www.primeportal.net/artillery/don/mpq10a_walk_1.htm>
It should work well at 2.4GHz for a Wi-Fi "shoot out". Got any more
sitting around?


--
Jeff Liebermann jeffl@cruzio.com
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:
> Radiosondes have two basic assumptions. The transmitter is always
> above the receiver and that antenna is always roughly vertically
> oriented.

Not so. The weather reporting radiosonde used in the 60s and 70s
aways drifted off to the horizon, driven by the prevailing wind.

The radio receiver was something like a ten foot diameter dish
under a plastic radome that tracked the radiosonde.

As i recall, they had a single tube transmitter that was frequency
modulated by the thermometer and air pressure was sensed by a
bellows that was mechanically connected to a rheostat that pulse
proportional modulated the signal. All this is going back over
thirty years ago when I played with the project.

Direction was resolved by the rotation coordinates of the dish.

On Apr 3, 6:02*pm, Jeff Liebermann <je...@cruzio.com> wrote:
> On Thu, 3 Apr 2008 08:12:00 -0700 (PDT), Adam Chapman
>
> <adam.chap...@student.manchester.ac.uk> wrote:
> >I do hope that Im not appearing to be lazy here, I've never had to
> >work in wireless systems as I am an aerodynamisist recently turned
> >image processing geek.
>
> If this is a skool project, you are expected to do your own research
> and calculations. *You don't learn much by having us doing it for you.
> If you have a *SPECIFIC* problem with some aspect of the project, feel
> free to ask. *However, the basic design in implimentation should be
> all your work.
>
> >I was expecting my question to have an easy
> >answer but as usual here wasn't so sorry and thank you for taking your
> >own time to help me.
>
> Welcome to engineering at its worst. *The URL I listed:
> <http://wireless.wikia.com/wiki/Wi-Fi#Link_Calculations>
> shows a simplified wireless link calculation. *You are apparently
> using 802.11b/g instead of VSB modulation for video (and data) so the
> examples should work. *Use this as the basis for your calcs. *However,
> please note that the resultant numbers are the *BEST* case
> calculations. *Real world situations only make things worse. *For
> example, the 2dBi gain of the antenna is actually the MAXIMUM gain of
> the antenna. *If you are off axis from the antenna pattern, the gain
> (and range) will be less. *Receiver sensitivity is never as good as
> they claim. *This should help:
> <http://802.11junk.com/jeffl/rx-sens/receiver%20sensitivity.htm>
> You will need to specify the other end of your radio link (equipment,
> coax, antenna) before I can help with the numbers. *It's really quite
> simple.
>
> >The camera is a Trendnet IP-TV301W model, specification at
> >http://trendnet.com/products/proddet...-IP301W&cat=48..
>
> OK. *802.11b/g. * Draws 7 watts (at 12V) and weighs 0.5kg. *Do you
> have any idea of how big a battery will need to be to supply 7 watts
> of continuous power? *4ea LIPO cell phone batteries will do the trick,
> but you'll only have perhaps 15 minutes of operating time. *To lift
> all this, the plane doesn't need to be huge, but it certainly won't be
> a styrofoam fly weight.
>
> >I don't physically have the camera yet because the university is still
> >processing the account, which in my experience can take a very long
> >time.
>
> The local university owes me some money from a project that is now 22
> years overdue. *Good luck.
>
> >If it is possible to estimate transmission ranges with certain
> >equipment, I would have an easier job justifying the expense to my
> >department.
>
> I don't see the connection between range and funding. *I suspect
> you'll do better with a feasability and finance study, than with a
> performance estimate.
>
> >The 2dBi antenna can be replaced, if there is a better type then I am
> >happy to use it. I would prefer an antenna that emits as spherical a
> >pattern as possible, otherwise we will have to limit aircraft
> >maneuevres.
>
> It really depends on what material you make the airplane from. *If RF
> transparent, a simple monopole (as supplied) will work. *When
> inverted, the signal will go through the aircraft. *However, if you
> make the airplane from reflective or absorptive materials, you'll need
> multiple antennas. *One 1/4 wave monopole on top and one on the bottom
> should be sufficient. *With a small ground plane under the antenna,
> the pattern should be mostly cardioid shaped. *If you have a wind
> resistance problem, you can use a small ceramic patch antenna instead.
> It is possible to model the antenna pattern using (free) antenna
> modeling tools:
> <http://home.ict.nl/~arivoors/>
> The sample files include a 747 aircraft (which will need to be
> scaled). *This is not exactly a trivial exercise, a potential time
> burning diversion, and is probably overkill for what you're
> attempting. *It's easy enough to construct a model, install the
> camera, and just play with the position of the antenna until it's a
> workable compromise. *
>
> Note that installing a bigger antenna on the airplane is not what you
> want. *Bigger antennas imply more gain. *You want hemispherical
> antenna pattern which requires a smaller or simpler antenna. *Here's
> an approximation of an isotropic antenna:
> <http://802.11junk.com/jeffl/antennas/isotropic/index.html>
> I think this is overkill and probably not practical on an airplane. If
> you're going to do work with the antenna, do it on the ground station.
>
> >I have just recieved more information from the competition organisers,
> >who tell me that all flying will be within 500m of the launch site and
> >flying is not permitted above 400ft (121.92 m) This gives the max.
> >Euclidean distance as 514.65m, although i expect we will be measuring
> >that distance on the aircraft with GPS, and with the civilian accuracy
> >limitations on GPS (~ +- 12m), I would suggest a target transmission
> >distance of 550m.
>
> >Due to safety rules we will never lose sight of the aircraft so we can
> >expect no obstacles between transmitter and reciever.
>
> If this is competition flying, it's also likely (but not guaranteed)
> that you'll also get minimal 2.4GHz interference. *It's traditional to
> confiscate the controllers during the competition to prevent sabotage.
> That works because RC has dedicated frequencies. *That's NOT the case
> with 2.4GHz, where there's a chance that some lunatic, with a portable
> wireless router, can crash your flying machine. *You can also lose
> control when the aircraft flys over a coffee shop wireless hot spot.
> (I'm assuming that you'll be controlling on 2.4GHz). *I sure hope this
> is going to be run in the middle of nowhere. *Testing it at skool,
> where there's lots of 2.4GHz interference, is going to be ummm...
> interesting.
>
> >I've been slowly writing this reply all day, and thinking a lot as i
> >do so.
>
> At the beginning of any project, leaps of faith, wild ideas, the
> shooting from the hip, are standard procedure. *Once the ideas are
> ossified, then you can be more studious and careful.
>
> >A helical antenna looks the best as it is the most isotropic,
>
> Too big, too much drag, too critical, poor gain to volume ratio. *If
> you're going to go to that level of complexity, think about two
> ceramic patch antennas with a -3dB Wilkinson combiner. *Two back to
> back cartoid patterns equal roughly a hemisphere.
>
> >although it is also pretty big for our aircraft. However even that has
> >+-45 degree 3dB lobe, so i might have to have the aircraft bank more
> >when closer to the centre of its circular mission area.
>
> Translation. *If you have a hole in the antenna pattern, you're going
> to lose control. *A helix also has no gain in the reverse direction,
> so you'll need two. *Hint: *Look at what's on a real airplane or
> guided missile.
>
> >The link calculator link from LR told me that if i put an antenna with
> >a 7dBi gain (like the one at _) on the UAV and at the ground station,
> >i will have a range of over 7km with a 100mW transmitter, which I
> >assume can be achieved using an in-line amplifier. Does this
> >calculator use the range in the direction of the strongest energy
> >emisiion from the antenna?
>
> I'm still missing some numbers. *See the example calcs on the URL I
> mentioned. *Copy the table of numbers and plug in YOUR numbers.
> Remember, those are the BEST case calculations. *Reality only makes it
> worse.
>
> >I guess that more than on antenna on the same aircraft with different
> >orientations would interfere with each others signals?
>
> If the two antennas cannot "see" each other, they will not mangle the
> combined pattern. *What other signals?
>
> Good luck. *Sounds like an interesting project. *Watch your weight and
> power consumption. *
> --
> Jeff Liebermann * * je...@cruzio.com
> 150 Felker St #D * *http://www.LearnByDestroying.com
> Santa Cruz CA 95060http://802.11junk.com
> Skype: JeffLiebermann * * AE6KS * *831-336-2558

I have found a commercially available patch antenna, here at
http://www.cisco.com/en/US/docs/wire...e/ant2485.html
and a groundstation antenna at http://www.radiolabs.com/products/wireless/waverv2.php
.
Now the cisco site I linked for the patch antenna does not say what
the Tx power is, althoug at a another site (http://www.cisco.com/en/US/
prod/collateral/wireless/ps7183/ps469/
product_data_sheet09186a008008883b.html) I read that the Cisco Aironet
2.4 GHz Bridge transmitter power is 20 dBm. I cant seem to find a
defintion for a bridge transmitter though, so im not sure if i know
the Tx power of the patch antenna or not. Does 20 dBm seem reasonable
for this antenna?


If the patch antenna power is 20dBm (which is the legal maximum in the
UK), then over a 550m range the SOM should be just below 28 dB
according to my calculations. Although I was aiming for 28 or above
the PER does not appear to be too bad.

Thanks again
Adam

DTC wrote:

> Jeff Liebermann wrote:
>
>> Radiosondes have two basic assumptions. The transmitter is always
>> above the receiver and that antenna is always roughly vertically
>> oriented.
>
> Not so. The weather reporting radiosonde used in the 60s and 70s
> aways drifted off to the horizon, driven by the prevailing wind.

Indeed, the antenna was vertical, but the pattern permitted
horizon to horizon coverage but without nulls overhead.

>
> The radio receiver was something like a ten foot diameter dish
> under a plastic radome that tracked the radiosonde.

The GMD-1 dish often was exposed and not in a radome.

>
> As i recall, they had a single tube transmitter that was frequency
> modulated by the thermometer and air pressure was sensed by a
> bellows that was mechanically connected to a rheostat that pulse
> proportional modulated the signal.

There was a baroswitch which selected the sensor to read based on
increments in altitude; the modulation was PRR. The oscillator
was a pencil triode in a cavity resonating at 1680 MHz and tuned
with a screw probe.

Michael

On Thu, 3 Apr 2008 16:13:32 -0700 (PDT), Adam Chapman
<adam.chapman@student.manchester.ac.uk> wrote:

>I read that the Cisco Aironet
>2.4 GHz Bridge transmitter power is 20 dBm. I cant seem to find a
>defintion for a bridge transmitter though, so im not sure if i know
>the Tx power of the patch antenna or not. Does 20 dBm seem reasonable
>for this antenna?

The power rating of an antenna is the point where the antenna can be
safely operated without melting, arcing, or self-destructing. There's
no way an antenna is going to do any of these at 20dBm (100
milliwatts).

>If the patch antenna power is 20dBm (which is the legal maximum in the
>UK), then over a 550m range the SOM should be just below 28 dB
>according to my calculations. Although I was aiming for 28 or above
>the PER does not appear to be too bad.

Antenna power handling ability has nothing to do with range.

Any antenna that has the proper gain, size, and weight characteristics
will work. It's up to you to determine the requirements.

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

On Thu, 03 Apr 2008 16:57:55 -0500, DTC <me@nothingtoseehere.zzx>
wrote:

>Jeff Liebermann wrote:
>> Radiosondes have two basic assumptions. The transmitter is always
>> above the receiver and that antenna is always roughly vertically
>> oriented.
>
>Not so. The weather reporting radiosonde used in the 60s and 70s
>aways drifted off to the horizon, driven by the prevailing wind.

Sure. Assuming a flat earth model, the tracking antenna cannot be
expected to dip much below horizontal. My point is that there was no
need for any RF to be radiated by the radiosonde ABOVE the horizon or
in an upwards direction. You can't make that assumption with a model
airplane, which can fly upside down, and does require RF to be
radiated in the upward direction.

>The radio receiver was something like a ten foot diameter dish
>under a plastic radome that tracked the radiosonde.

I have one in the closet somewhere. I'll dig it out and take some
photos (later). It's amazingly crude and cheaply made.

>As i recall, they had a single tube transmitter that was frequency
>modulated by the thermometer and air pressure was sensed by a
>bellows that was mechanically connected to a rheostat that pulse
>proportional modulated the signal. All this is going back over
>thirty years ago when I played with the project.

Tube? Thermionic Valve? Whazzat? Dis is da space age. We don't do
no stinkin tubes.

>Direction was resolved by the rotation coordinates of the dish.


--
Jeff Liebermann jeffl@cruzio.com
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:

<snip>
>
> Tube? Thermionic Valve? Whazzat? Dis is da space age. We don't do
> no stinkin tubes.

Ground support computers for the first few Redstone/Mercury launches
included Bendix G-15 vacuum tube machines; most of the hardware
was in fact tube-based. IIRC, the Mercury capsule even contained
some tubes.

Michael

msg wrote:
> There was a baroswitch which selected the sensor to read based on
> increments in altitude; the modulation was PRR.

That's the phrase I was trying to remember, Pulse Repletion Rate.

Adam Chapman wrote:>
> The camera is a Trendnet IP-TV301W model, specification at
> http://trendnet.com/products/proddet...-IP301W&cat=48.

It's been interesting reading....
but was wondering why you went with a larger heavy camera
vs the tiny 2.4Ghz spycams you see advertised.

Do you only need a webcam for a visual view,
OR
is this part of the onboard autonomous navigation
and you need a "good" camera image to use for processing ?

Adam Chapman wrote:
> Thanks to all of you, I replied to this particular post because it had
> the most questions for me to answer.
> I do hope that Im not appearing to be lazy here, I've never had to
> work in wireless systems as I am an aerodynamisist recently turned
> image processing geek. I was expecting my question to have an easy
> answer but as usual here wasn't so sorry and thank you for taking your
> own time to help me.
>
> On Apr 2, 11:54 pm, Jeff Liebermann <je...@cruzio.com> wrote:
>> On Wed, 2 Apr 2008 08:00:06 -0700 (PDT), Adam Chapman
>>
>> <adam.chap...@student.manchester.ac.uk> wrote:
>>> I've ordered a wireless webcam that will be out onboard an
>>> autonomous aircraft for a university project.
>>
>> I've done that. You're about to have a battery problem.
>>
>>> The camera has a "2dBi Diversity Antenna" and transmits video over
>>> an IP protocol in the 2.4-2.4835 GHz range.
>>
>> Duz this camera have a manufacturer and a model number? A URL with
>> the specifications would be nice.
>>
>
> The camera is a Trendnet IP-TV301W model, specification at
> http://trendnet.com/products/proddet...-IP301W&cat=48.
> I don't physically have the camera yet because the university is still
> processing the account, which in my experience can take a very long
> time. If it is possible to estimate transmission ranges with certain
> equipment, I would have an easier job justifying the expense to my
> department.
>
>> 2dBi is a simple monopole antenna. It has a radiation pattern that
>> looks like a donut. There's a big null when in line with the
>> antenna, such as when the aircraft is flying directly overhead.
>>
>
> The 2dBi antenna can be replaced, if there is a better type then I am
> happy to use it. I would prefer an antenna that emits as spherical a
> pattern as possible, otherwise we will have to limit aircraft
> maneuevres.
>
>
>
>>> Now the aircraft needs to operate in a 500x500m area, although I
>>> expect that my ground station computer will be placed some distance
>>> away from the operating area.
>>
>> I have this thing about numbers. How far is "some distance"? How
>> high does the air thing have to fly? What's the MAXIMUM distance you
>> expect to see an image?
>>
>
> I have just recieved more information from the competition organisers,
> who tell me that all flying will be within 500m of the launch site and
> flying is not permitted above 400ft (121.92 m) This gives the max.
> Euclidean distance as 514.65m, although i expect we will be measuring
> that distance on the aircraft with GPS, and with the civilian accuracy
> limitations on GPS (~ +- 12m), I would suggest a target transmission
> distance of 550m.
>
> Due to safety rules we will never lose sight of the aircraft so we can
> expect no obstacles between transmitter and reciever.
>
> I've been slowly writing this reply all day, and thinking a lot as i
> do so. A helical antenna looks the best as it is the most isotropic,
> although it is also pretty big for our aircraft. However even that has
> +-45 degree 3dB lobe, so i might have to have the aircraft bank more
> when closer to the centre of its circular mission area.
>
> The link calculator link from LR told me that if i put an antenna with
> a 7dBi gain (like the one at _) on the UAV and at the ground station,
> i will have a range of over 7km with a 100mW transmitter, which I
> assume can be achieved using an in-line amplifier. Does this
> calculator use the range in the direction of the strongest energy
> emisiion from the antenna?
>
> I guess that more than on antenna on the same aircraft with different
> orientations would interfere with each others signals?
>

how big is the plane ?
do you have a UK link for the project, or ph