2.4GHz antenna problem

[martin griffith]

I want to put a camera and 2.4GHz transmitter on a windsurf sail,
pointing down towards the sailor so I can see what happens when they
do a loop


I know relatively little about 2.4G stuff, so what sort of Rx antenna
wiil I require as the Tx antenna will revolve through at least 360
degree...see
http://uk.geocities.com/martingriffith/splashcam.htm

I found these simple designs on the web
http://www.packetattack.com/wireless.html

a yagi, a circular polarised , a pringle can and a parabolic antenna
which type would be most appropriate?

The antenna will be mounted on a tripod, so that it can follow the
action.


thanks

martin

 

[Winfield Hill]

martin griffith wrote...

I want to put a camera and 2.4GHz transmitter on a windsurf sail,
pointing down towards the sailor so I can see what happens when they
do a loop

And the "sailer" is...? :>) Nice to see you're still alive and
kicking, Martin!

I know relatively little about 2.4G stuff, so what sort of Rx antenna
wiil I require as the Tx antenna will revolve through at least 360
degree...see http://uk.geocities.com/martingriffith/splashcam.htm

Why consider directional antennas when the source will be taking
on all angles (including underwater I assume? :>) Most of these
designs only give you +6 to 9dB gain anyway, easily gotten from a
more powerful transmitter power. With omni antennas you're legal
up to 1W, which is 10 to 20x more power than the wimpy units you
normally see, arguably more effective than a directional antenna
anyway.

Some folks (LinkSys?) offer power step-up units at just over $100.
One issue, they need an internal 2.5GHz T/R switch, which is a
tricky component. There are a few homebrew designs on the web,
but if you make one watch out for proper 2.5GHz "wiring."

Another point, across the open ocean to shore you should get more
range anyway, no trees, etc. Have you tried it yet?

I found these simple designs on the web
http://www.packetattack.com/wireless.html

a yagi, a circular polarised , a pringle can and a parabolic
antenna which type would be most appropriate?

Have you considered windage?

Thanks,
- Win

whill_at_picovolt-dot-com

 

[Tim Auton]

martin griffith wrote... [snip]

I know relatively little about 2.4G stuff, so what sort of Rx antenna
wiil I require as the Tx antenna will revolve through at least 360
degree...see http://uk.geocities.com/martingriffith/splashcam.htm

Why consider directional antennas when the source will be taking
on all angles (including underwater I assume? :>)

I don't see the point in not going for a directional Rx antenna of
some description, it's not like the windsurfer is going to end up on
the beach behind the Rx so it's more gain without having to carry more
kit on the windsurfer.

The TX spinning through all angles would affect polarization, but
aren't most (all?) omnis polarized too? I can see how an onmi would be
better for a moving target, but not for a rotating one. Perhaps I
don't know enough about polarization.

Most of these
designs only give you +6 to 9dB gain anyway, easily gotten from a
more powerful transmitter power. With omni antennas you're legal
up to 1W, which is 10 to 20x more power than the wimpy units you
normally see, arguably more effective than a directional antenna
anyway.

It's the Rx antenna he's asking about, I presume there are no legal
limits on gain at that end (I can't see any logical reason for it and
there's no restriction in the UK on Rx, only Tx).

Have you considered windage?

At first I read that as the ballistics definition: "The point or
degree at which the wind gauge or sight of a rifle or gun must be set
to compensate for the effect of the wind" and wondered just how much
you knew about photons

The 2.4GHz antennas I've built for video have been for a different
application - robots driving around on the ground. For that I went
with vertical polarization, a 1/4 wave whip on the Tx and a diacone
(omnidirectional, compact, good gain and they look cool too!) on the
Rx. Given this experience wasn't in a commercial environment I
wouldn't take the following advice as gospel, but here goes anyway.

For the OP's application I'd go for horizontal polarization (left to
right in the OP's images: perpendicular to the vertical and
longitudinal axes of the windsurfer) with a flexible whip or dipole
antenna tough enough to take the punishment. For the Rx end a
horizontally polarized Yagi with the right combination of
directionality and gain. The right combination is left as an exercise
for the reader

A parabola would probably give more gain but you'd have to be aiming
it all the time and on a windy day that wouldn't be fun (the "windage"
effect Win was getting at I presume). Horizontal polarization wouldn't
change as the windsurfer flipped over, whereas vertical would be
rotating with respect to the receiver so your gain would vary
(theoretically dropping to zero as the mast pointed towards the
receiver).


Tim

 

[martin griffith]

martin griffith wrote...

And the "sailer" is...? :>) Nice to see you're still alive and
kicking, Martin!

not me, i'm the camera dude, but still thinking of starting
kitesurfing!

Why consider directional antennas when the source will be taking
on all angles (including underwater I assume? :>) Most of these
designs only give you +6 to 9dB gain anyway, easily gotten from a
more powerful transmitter power. With omni antennas you're legal
up to 1W, which is 10 to 20x more power than the wimpy units you
normally see, arguably more effective than a directional antenna
anyway.

I need a small Tx on the sail, powered by a couple of AA cells, the
10dB Tx is 40ma @5V, 120ma @20dB, not including the camera power.
and weight is important, not to unbalance the sail, most masts are in
the 4.3M length, so 500g half way up the mast may make a difference to
its handling (

Some folks (LinkSys?) offer power step-up units at just over $100.
One issue, they need an internal 2.5GHz T/R switch, which is a
tricky component. There are a few homebrew designs on the web,
but if you make one watch out for proper 2.5GHz "wiring."

Another point, across the open ocean to shore you should get more
range anyway, no trees, etc. Have you tried it yet?

not yet, just working on the waterproofing ATM

Have you considered windage?

yep, probably from too many roast potatoes!

Thanks,
- Win

whill_at_picovolt-dot-com

thanks

martin

 

[martin griffith]

martin griffith wrote... [snip]

I know relatively little about 2.4G stuff, so what sort of Rx antenna
wiil I require as the Tx antenna will revolve through at least 360
degree...see http://uk.geocities.com/martingriffith/splashcam.htm

Why consider directional antennas when the source will be taking
on all angles (including underwater I assume? :>)

I don't see the point in not going for a directional Rx antenna of
some description, it's not like the windsurfer is going to end up on
the beach behind the Rx so it's more gain without having to carry more
kit on the windsurfer.

The TX spinning through all angles would affect polarization, but
aren't most (all?) omnis polarized too? I can see how an onmi would be
better for a moving target, but not for a rotating one. Perhaps I
don't know enough about polarization.

Most of these snip

A parabola would probably give more gain but you'd have to be aiming
it all the time and on a windy day that wouldn't be fun (the "windage"
effect Win was getting at I presume). Horizontal polarization wouldn't
change as the windsurfer flipped over, whereas vertical would be
rotating with respect to the receiver so your gain would vary
(theoretically dropping to zero as the mast pointed towards the
receiver).


Tim

Thanks tim

I'm still confused about circular polarised antennas, would these help
me?


thanks

martin

 

[Winfield Hill]

martin griffith wrote...

I need a small Tx on the sail, powered by a couple of AA cells, the
10dB Tx is 40ma @5V, 120ma @20dB, not including the camera power.

When reading your post seeing 2.4GHz, I first assumed 802.11b data
transmission, but now I see you mean analog transmission, e.g., like
those little X10 thingamajigs. Going for more power still seems a
good idea, and easier since the 2.4GHz transmission is one way only.
You can bring DC power from some C cells, etc., up the mast, right?

Thanks,
- Win

whill_at_picovolt-dot-com

 

[Ian Stirling]

not me, i'm the camera dude, but still thinking of starting
kitesurfing!

What's wrong with a camcorder in a sealed box, with a small camera feeding
the video-in input?

 

[Tim Auton]

martin griffith wrote... [snip]
I know relatively little about 2.4G stuff, so what sort of Rx antenna
wiil I require as the Tx antenna will revolve through at least 360
degree...see http://uk.geocities.com/martingriffith/splashcam.htm

Why consider directional antennas when the source will be taking
on all angles (including underwater I assume? :>)

I don't see the point in not going for a directional Rx antenna of
some description, it's not like the windsurfer is going to end up on
the beach behind the Rx so it's more gain without having to carry more
kit on the windsurfer.

The TX spinning through all angles would affect polarization, but
aren't most (all?) omnis polarized too? I can see how an onmi would be
better for a moving target, but not for a rotating one. Perhaps I
don't know enough about polarization.

Most of these snip

A parabola would probably give more gain but you'd have to be aiming
it all the time and on a windy day that wouldn't be fun (the "windage"
effect Win was getting at I presume). Horizontal polarization wouldn't
change as the windsurfer flipped over, whereas vertical would be
rotating with respect to the receiver so your gain would vary
(theoretically dropping to zero as the mast pointed towards the
receiver).

I'm still confused about circular polarised antennas, would these help
me?

What I think I know of polarisation isn't enough to give a definitive,
or even useful, answer to this. I'm going to have to pass on this one
- anybody else care to contribute?

The best answer I can think of (with some, but not enough, theory
behind it) is "perhaps". That's really no answer at all, I know. I did
some more reading about polarisation and all that did was confirm I
really don't know enough about it and how it might affect your
application. For the sake of a usenet post I can't be arsed to learn
more. Sorry. Surely there must be someone with experience or at least
good references here?


Tim

 

[Fred Bloggs]

martin griffith wrote...
[snip]

I know relatively little about 2.4G stuff, so what sort of Rx antenna
wiil I require as the Tx antenna will revolve through at least 360
degree...see http://uk.geocities.com/martingriffith/splashcam.htm

Why consider directional antennas when the source will be taking
on all angles (including underwater I assume? :>)

I don't see the point in not going for a directional Rx antenna of
some description, it's not like the windsurfer is going to end up on
the beach behind the Rx so it's more gain without having to carry more
kit on the windsurfer.

The TX spinning through all angles would affect polarization, but
aren't most (all?) omnis polarized too? I can see how an onmi would be
better for a moving target, but not for a rotating one. Perhaps I
don't know enough about polarization.

Most of these snip

A parabola would probably give more gain but you'd have to be aiming
it all the time and on a windy day that wouldn't be fun (the "windage"
effect Win was getting at I presume). Horizontal polarization wouldn't
change as the windsurfer flipped over, whereas vertical would be
rotating with respect to the receiver so your gain would vary
(theoretically dropping to zero as the mast pointed towards the
receiver).


Tim

Thanks tim

I'm still confused about circular polarised antennas, would these help
me?


thanks

martin

That would be better but may not be necessary. The polarization is just
another loss factor that adds to the equation when there is a mismatch
between the tx and rx orientation. If you go with two vertically
polarized omnidirectionals then this loss factor does not become
significant until the tx antenna tips way over to something like 60o
from vertical or more, and even then the polarization loss pales in
comparison to path loss of 20xLog(4pi x range/lamda). You can consider
the polarization mismatch loss to be equivalent to an added range, and
at your frequency, the craft will be on its side water by the time this
adds up to maybe 200 meters. If you can find a circularly polarized
antenna, and use omni directional on receive, the gain will be down by
something like 6dB due lesser antenna gain and polarization mismatch
loss between circular and vertical, but it will be impervious to the
glider orientation off vertical. If you know your range is never going
to exceed say 200m, then sizing for 500m on match should do it. Don't
hold me to the numbers- do your own research

 

[Winfield Hill]

martin griffith wrote...

I want to put a camera and 2.4GHz transmitter on a windsurf sail,
pointing down towards the sailor so I can see what happens when they
do a loop...
a yagi, a circular polarised , a pringle can and a parabolic antenna
which type would be most appropriate? The antenna will be mounted
on a tripod, so that it can follow the action.

Aha, finally I realize you mean the high-gain antenna will be onshore!
Where it should be, of course. I have had excellent results with the
+24dB parabolics that have open-screen in construction. I found some
excellent commercial versions on eBay for on the order of $100 to $120.

Thanks,
- Win

whill_at_picovolt-dot-com

 

[Marc H.Popek]

The key statement is "loops of the windsurfer aka radio" to maintain a
constant radio contact you will need circularly polarized antennas on both
ends.

Marco

for amazing antenna detail go to;
www.fwt.niat.net

 

[Frank Raffaeli]

The key statement is "loops of the windsurfer aka radio" to maintain a
constant radio contact you will need circularly polarized antennas on both
ends.

Marco

for amazing antenna detail go to;
www.fwt.niat.net

Nice pictures.

There are many excellent suggestion in this thread; however, what you
are attempting is inconsistent with what I know about microwave signal
propagation.

First, to increase reliability, lower the frequency. As anyone who has
tried a portable TV in a moving car will confirm, the picture is a lot
more stable on the lower channels (60-90 MHz), all else being equal.

The water will contribute to the same type of multipath as ground
effects, only worse. Even though the rx antenna can be made more
directional, 2.4 GHz is not the frequency to use. Go to a low or high
VHF channel, use top part of the the mast as the (linearly polarized)
antenna, and use a circularly polarized antenna at the receiver.

If licensing is a problem at low VHF, at least try for 902-928 MHz.
The multipath effects will be compounded and severe relative to low
VHF, but better than 2.4 GHz.

If you have no choice but 2.4 GHz, use a linearly polarized tx
antenna, and a circularly polarized rx antenna. In the propagation
studies we have done at 2.4 GHz, using a moving tx or rx, we concluded
that a CP antenna at one end and linear (variable orientation) at the
other improves the "worst case" fade margin 16 dB over a
linear-to-linear. This is despite the power losses due to polarization
mismatch.

Frank Raffaeli
http://www.aomwireless.com/

 

[GrahamH]

What's wrong with a camcorder in a sealed box, with a small camera feeding
the video-in input?

Very good point. Or even a micro-DV camcorder on the mast. Best quality and
no problems with H2O and 2.4GHz which is a bad combination. Water absorbs
2.4GHz extremely well. You will most likely lose signal on your radio link
if the antenna dips below a wave crest. Spray may also be a problem. And
what about waves intruding into the fresnel zone? A camcorder is a bit more
expensive but consider the all-in-one construction, no antenna equipment, no
tracking problems, no receiving equipment required.

Seal the camera inside a watertight industrial box with clear lid and
start-stop recording using the IR remote.

 

[Sylvan Butler]

Aha, finally I realize you mean the high-gain antenna will be onshore!
Where it should be, of course. I have had excellent results with the
+24dB parabolics that have open-screen in construction. I found some
excellent commercial versions on eBay for on the order of $100 to $120.

I've had good results with http://www.fab-corp.com/ (more like $80).

sdb

--
| Sylvan Butler | Not speaking for Hewlett-Packard | sbutler-boi.hp.com |
| Watch out for my e-mail address. Thank UCE. >>>> change ^ to @ <<<< |
It may be better to live under robber barons than under omnipotent moral
busybodies. The robber baron's cruelty may sometimes sleep, his
cupidity may at some point be satiated; but those who torment us for our
own good will torment us without end, for they do so with the approval
of their consciences. -- C. S. Lewis

 

[Winfield Hill]

Sylvan Butler wrote...

I've had good results with http://www.fab-corp.com/ (more like $80).

I'm impressed, the $80 units look good! There must be a big market
for high-gain antennas for their prices to have become so attractive.

Thanks,
- Win

whill_at_picovolt-dot-com