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