Q&A on my setup

[ShadesOfGray]

Hey guys,
So, a few things have changed regarding the setup I'm planning, and I wanted to run through it and see what suggestions or changes you'd all propose. As of this writing, we've ordered the 900 MHz stuff, the Wifi stuff, and I'm building an order for the 1.2 GHz stuff.

I'd like to get a reliable signal up to at least 1.5 miles line of sight. 2 miles would be a nice cushion.

Here's what I've got in mind:

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1. Forward Facing Camera & Tx: KX 191 on 900 MHz

Camera: KX-191 on a gimbal from RangeVideo (http://www.rangevideo.com/index.php?main_page=product_info&cPath=47&products_id=132), to be mounted on the bottom of the fuselage

Transmitter: 500 mW, 900 MHz (http://futurehobbies.com/index.php?page=shop.product_details&flypage=flypage.tpl&product_id=116&category_id=19&option=com_virtuemart&Itemid=53)

Receiver: 8 dBi patch (http://futurehobbies.com/index.php?page=shop.product_details&flypage=flypage.tpl&product_id=134&category_id=22&option=com_virtuemart&Itemid=53)

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2. Downward Facing Camera & Tx: Aiptek A-HD+ on 1.2 GHz

Camera: Aiptek A-HD+, sending analog to the tx, recording simulataneously
On a gimbal from Servocity.

Transmitter: Lawmate 500 mW, 1.2 GHz (http://www.nghobbies.com/cart/index.php?main_page=product_info&cPath=50&products_id=284&zenid=0ff499a30acb39064f1396ae9b435f7a)

Receiver: 8 dBi patch (http://www.l-com.com/item.aspx?id=20248)

======================

3. Data Connection and Primary Control Tx/rx: Wifi on 2.4 GHz

Transmitter: Wifi USB Stick, 2.4 GHz (http://www.sparklan.com/data/prod_data/257/prod_data.pdf)

Receiver: 24 dBi grid antenna (http://gnswireless.com/GNS1405.htm)

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4. Primary GPS receiver
Deluo GPS Lite or similar (http://www.deluo.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=DE&Product_Code=GPSU&Category_Code=Gr)

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5. Standby GPS Receiver/Transmitter
441 MHz Beeline GPS Rx/Tx (http://bigredbee.com/BeeLineGPS.htm)

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6. Standby Controller: Hitec on 72 MHz

Transmitter: 72 MHz - Hitec Eclipse 7 QPCM (http://www.hobby-lobby.com/hitec.htm)

Receiver: 72 MHz - Hitec Supreme IIs (http://www.hobby-lobby.com/receiver.htm)

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Because of a design constraint, we may not be able to mount the antennas on the airplane straight up and down; the airplane has to fit inside a rocket. They could possibly be sticking down from the bottom of the fuselage at an angle, or sticking out the tail of the airplane.... or spring-loaded somehow.... It's going to be messy, whatever it is. Still working on that part of it.

As you all know, I'm pretty new to all of this, so I'm all ears for any tips, suggestions, concerns, etc. Lemme know what you think.
Thanks,
-Will

[wolffman73]

What do you mean when you say the airplane must fit inside a rocket?

[ShadesOfGray]

Heh. Quite literally, the airplane is to fit inside a rocket.

It's for a NASA competition where the objective is to fly a scientific payload inside a rocket. Our rocket's payload is the airplane, lol. The airplane's wing is on a rotating mechanism, it has a folding propeller, and the V-tail's are hinged to rotate backwards in line with the fuselage. The airplane is to be packaged inside a 10"-diameter, 14'-tall rocket that carries it to altitude. The project title is "Rocket Launched Reconnaissance UAV."

http://www.vanderbilt.edu/USLI

http://www.vanderbilt.edu/USLI/gallery/inthelab/deployment_subsystem.jpg

http://www.vanderbilt.edu/USLI/gallery/logo.jpg

[ssassen]

Don't mean to rain on your parade, but a WiFi USB stick (unless coupled with an external antenna) is positively not going to give you the range you're looking for.

Cheers,

Sander.

[ShadesOfGray]

Yeah, I had kind of anticipated that, but we hadn't had time to test it definitively yet. What if we connect a 5 dBi or 7 dBi antenna? That should cover it, right? I was thinking of a setup somewhat like documented here:
http://ronobvious.livejournal.com/296.html
http://www.xp11.com/g54/g54.htm

If the wifi antenna is the only real problem with my proposed setup right now then I feel like we're on the right track. Originally I was going to leave all of this to a guy who knows more about electronics and antennas and wireless communication than I do, but he's kind of dropped the ball while he works on some other stuff so I'm having to figure this out by myself. :[ Not quite my cup of tea, obviously.

Thanks for the tips, as always.
-Will

[ssassen]

Will,

I'd get something which has a SMA connector mounted, rather than mod an adapter, as you'll induce a lot of losses. You can then always replace the stock antenna with something else. However maximum output power is just 11dBm, that's not a whole lot. What is the intended height/distance for the UAV to be released? That'll give us an idea whether this has a chance of working.

Cheers,

Sander.

[ShadesOfGray]

Right now the plan calls for the UAV to be released at 2,000'. If everything goes perfectly, it'll be almost directly overhead. In reality it'll probably be 2,000' high and 400' downwind of where we're set up.

I'll look at some other USB sticks, but the catch is it has to be friendly with our 500 MHz computer running some simplified version of linux (whose name I forgot). Our real computer engineer already picked out the USB stick he wanted, but we can always get another one if I track down one that will work and has an SMA connector.

Just how bad are the losses, if an extenna antenna is added tidily? Any ballparks? 20%? 30%?

[ShadesOfGray]

Also, as to the 11 dBm number, you got that from the datasheet for the device, eh? Will different devices have different amplifications? Does that mean that I shouldn't use an omni antenna any more powerful than 11 dBi?

Thanks,
-Will

[skunkworks2006]

Will, I can't help you much, but I wanted to say that I'm a bit jealous of your project. I'm not on the aerospace career tract any longer, but once was and this sounds like a fun project.
Often antenna connections can be de-soldered and replaced with the desired connection if you can identify where everything is connected. I agree that you want to eliminate as much cable gack and adapters as possible to keep the signal clean.
I would think that a spring loaded antenna might be a good solution, or possibly a stacked wheel antenna. http://www.hamtv.com/wheel.html

[ShadesOfGray]

Thanks. Yeah, it's a very cool project, and I enjoy working on it immensely. But I've discovered that I don't know half as much as I thought I knew. And I'm working with a largeish group (12), and rapidly finding that I can't really depend on anyone for anything. :[

Here's another thought for the USB wifi: 500 mW, already set up w/SMA adapter, comes with 8dBi antenna.
http://www.amazon.com/802-11b-Wireless-Adapter-9dBi-Strongest/dp/B001O9X9EU

The only question is whether we can make it work with our little linux computer...

What say ye?

Thanks,
-Will

[ShadesOfGray]

Oh, and what about the 8 dBi patch antennas for the video rx? Will that be sufficient for up to 1.5 miles or so, if I use a 500 mW transmitter for each video source?

Thanks for all the help,
-Will

[ShadesOfGray]

Aight, found a USB-wifi device better suited to our needs:
http://www.amazon.com/802-11b-Wireless-Adapter-9dBi-Strongest/dp/B001O9X9EU

In other news, I also put together a pretty sweet block diagram of all the various electronic systems in the air and on the ground per the current plan. It details some of the basic specs of all the hardware we're using, and hopefully ya'll will make some more observations/suggestions based on this easy-to-interpret map of the system that we've got in mind:

http://www.vanderbilt.edu/USLI/gallery/inthelab/news/2-11-09/uberblock.jpg

[ssassen]

Pie-charts, block-diagrams, flow-charts, love 'm!

A few comments: first the amount of wireless RF links between the groundstation and the UAV. Do you really need that many? Each is a potential point of failure and having that many different bands combined in a single plane is asking for trouble, as interference between the various RF devices *will* occur, the question is whether that'll interfere with the proper functioning of the various devices.

For example the audio channel(s) on the video Tx can be used for telemetry, so GPS data can be send through that. So take another close look at the block diagram and see where you can use existing equipment in a double role.

Cheers,

Sander.

[ShadesOfGray]

Hmmm, worth thinking about definitely. There are two main reasons we have so many different communication links between the ground station and the UAV:
1. Redundancy. The people who fund us want very complete failure charts and they want to see that our plane isn't going to crash unless multiple independent systems fail. We could use a USB webcam for the forward facing camera, and transmit that through the Wifi, but then if the wifi fails we'll have no way of piloting the plane. By using a tried-and-true 900 mhz link for the forward-facing camera, and having a 72 mhz standby receiver, in the event that the wifi uplink fails, and/or the recon camera fails, and/or all the other shite hits the fan, we'll still be OK, provided everything works.
2. We also originally wanted to send the recon camera through the wifi, but our SBC isn't fast enough to convert the analog video to digital in realtime; it has to be transmitted as analog and then we recover the HD version once the plane lands.

Worth thinking about, though. I'll have to look in to using the audio channels from the vtx for the GPS, but I don't think that'd save us any communication links, because we still need the wifi regardless, and we want to have the 441 MHz standby GPS in case the wifi fails....

Thanks for the tips. I'm still all ears for other suggestions or concerns.
Thanks again,
-Will

[ShadesOfGray]

Oh yeah, and P.S. are my 8 dBi patch antennas gonna be sufficient for 1.5-2.0 miles range line of sight?
Thanks for all the help,
-Will

[ssassen]

Will,

are my 8 dBi patch antennas gonna be sufficient for 1.5-2.0 miles range line of sight?

Yes, that should be sufficient.

Cheers,

Sander.

[ShadesOfGray]

OK, great. Thanks again for all the help.
-Will