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Old Nov 16, 2010, 02:13 PM
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Dos Hermanas (Sevilla)
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Great work Alex!

Patrick
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Old Nov 16, 2010, 02:16 PM
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Netherlands, NH, Edam
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Alex,

Nice to finally see you in the flesh!

Cheers,

Sander.
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Old Nov 16, 2010, 04:01 PM
THEY MOSTLY COME OUT AT NIGHT
chimaera's Avatar
Kaysville, Utah
Joined Jul 2005
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How well does this do at long distances? could be interesting with grids.
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Old Nov 16, 2010, 04:12 PM
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Alex,

Can you check/confirm your parts list to your schmetic (post #5)
http://www.rcgroups.com/forums/showp...04&postcount=5

In the parts list, you say 6 x 15k resistors - I count 4 in the schematic?
Also, you list 1 x 270k resistor - I don't see it in the schematic, although I see a 200k resistor in the schematic but not in the parts list?

Am I missing something?

I'm intend to build one, just because... well... it's simple!
I'm going to go with circular polarisation, both on the VRx and the VTx.

Nigel.
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Old Nov 16, 2010, 04:34 PM
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Amherst, VA
Joined Jun 2006
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There is no 30K resistor. You use two 15Ks in series for that. I used a 270k resistor in my controller. The 200K on the schematic can be swapped for the 270K. This part isn't critical. It just regulates the tracker duty cycle. I'd probably go with the 200K.

-Alex
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Old Nov 16, 2010, 04:37 PM
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Canada, BC, Victoria
Joined Feb 2008
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Excellent work Alex!!! That is honestly, very impressive work. Hopefully I can make some time this winter or next spring to build one!

I too want to let you know that I admire your thankfulness to Christ on this project and for you talent and inginuity. I'm also a Christian and it makes me extremely happy to see others standing-up for their faith, even if it's just on some geeky FPV forums.

God bless & an excellent job well done!

Travis
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Old Nov 16, 2010, 05:40 PM
It just keeps getting better!
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Eureka, CA
Joined Oct 2002
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Very very nice!
Your inexpensive antenna designs keep it affordable.
It should be great for use with planes that lack GPS.
It can even give you an idea of where your plane is!
Now for a range test.
-Dave
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Old Nov 16, 2010, 10:19 PM
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I simulated a range test to well beyond video feed range by placing the antenna behind a hill and two garage walls 90 degrees out of polarization on a dead battery.

The farthest I flight tested it was 1 mile. I know it can go further, but I didn't have my RSSI hooked up and was on 72 MHz.

-Alex
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Old Nov 16, 2010, 10:35 PM
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Quote:
Originally Posted by Eganwp View Post
Excellent work Alex!!! That is honestly, very impressive work. Hopefully I can make some time this winter or next spring to build one!

I too want to let you know that I admire your thankfulness to Christ on this project and for you talent and inginuity. I'm also a Christian and it makes me extremely happy to see others standing-up for their faith, even if it's just on some geeky FPV forums.

God bless & an excellent job well done!

Travis
This project was one that should have never been successful on my own. I knew it was over my head when I started. However, it seemed every time I would pray for a solution I had it shortly after. Many times I was ready to give up. I burned several H-bridge chips, couldn't get my planetary gearbox to spin (which I later abandoned), had calibration issues, my turn table would refuse to turn (That center bolt is critical to getting this thing to spin, by the way), and a slew of other problems.

However, now it works phenomenally well. It works even better than I had hoped for. I even went out and bought a garage door opener (I found one for $0.57!) to use as a remote shut down, which I realize I will never need.

Some would call it dumb luck. But there were so many things that had to fall in order for me to got to this point. For example, my first ever video RX had a Comtech module in it (which happens to be the easiest to mess with). Martin Y mentioned the idea almost a year ago in my diversity controller thread. I then happened to become an antenna guru based on making a dipole successfully, which admittedly, I never wanted a boost in performance, just wanted to see if I could do it. Or how about Mr. RC-CAM mentioning the potentiometer to use for RSSI calibration which makes this possible (he mentioned it during the diversity controller design as a passing note).

I didn't get lucky. I had help

-Alex
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Old Nov 17, 2010, 08:56 AM
Whats the wrst that can happn?
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Chicago, IL USA
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Alex, good job and God bless! There's a fine line between luck, coincidence and miracles, it's just a matter of what you're willing to believe...or have faith in

Now I have to re-examine my faith in GPS tracking versus signal strength tracking.
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Old Nov 17, 2010, 10:40 AM
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USA, IN, Bloomington
Joined Aug 2007
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work with DUO 2400

Sander said that I could pull off the RSSI from the two receivers in my DUO 2400:

http://www.readymaderc.com/store/ind...products_id=58

I've not been brave enough to do it yet, but if I did could I use it as part of a tracker?
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Old Nov 17, 2010, 10:47 AM
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Possibly. There are two ways to find out:

1. Open it up and get the part number off of the RX modules inside then post them here.

2. Just try it.

A sync check diversity would eliminate the need for the third antenna. You would aim the antennas at a lesser angle as well, perhaps 45 degrees apart.

As always, I will help you with this. If you do build one, I will include it in the original tutorial as an alternative to my method.

-Alex
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Old Nov 17, 2010, 11:04 AM
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Quote:
Originally Posted by IBCrazy View Post
Possibly. There are two ways to find out:

1. Open it up and get the part number off of the RX modules inside then post them here.


-Alex
From Sander via PM a few months ago:

Yes, you can tap into the RSSI output of the Rx modules, they're Airwave AWM620 or AWM625, consult their datasheet for the pinout. Just hook up one antenna and leave the other input disconnected, then look at the RSSI output of the Rx that is connected to an antenna, use a high impedance (>100Kohm) DVM to measure the RSSI voltage.


Source for datasheet:
http://www.nghobbies.com/cart/index....products_id=22

RSSI is pin 7
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Old Nov 17, 2010, 11:56 AM
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There are a few problems:

1. Close range resolution is going to be a little sketchy, which I guess doesn't matter much. The highest signal it can detect is -45dbm. So up near that range the resolution is likely going to be poor, but acceptable condiering the close range signal strenth is already going to be good.

2. There is no information on how the RSSI is scaled other than it is an inverse scale from 1.5 to 3.5V. I found with the cheap knock off modules in my 900MHz RX units, that the AGC (RSSI) was not scaled evenly.

To know if this is going to work, you need to make a quick table:

Use two identical antennas on your RX unit and a single omni on your TX. If you chose directional antennas on your RX, aim them directly at the TX. Take RSSI readings WITHOUT TOUCHING THE RX ANTENNAS at various signal strengths. You can use techniques such as turning the TX antenna on it's side (loss of polarization) and placing objects (such as walls, hills, barriers) as well as distance to get your data points. 4 points should be sufficient. You will need one high strength, one low strength signal, and two somewhere in the middle. Be sure to turn your cell phone off when doing this test as it will affect the RSSI values.

Write the RSSIs and compare them at each signal strength. They should scale evenly (even if their voltages differ a little). If they scale evenly, tracker should work fine. If not, it won't.

How to tell if the scale is equal:

RSSI#1/RSSI#2 = scale factor

This does not mean they must be equal! If the scale factor changes with your datapoints, the the RSSIs are not scaled evenly and the tracker may not work well. If the scale factor is relatively constant (ie variance less than 10%) then the tracker will work fine.

-Alex
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Old Nov 17, 2010, 12:28 PM
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USA, IN, Bloomington
Joined Aug 2007
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multiplex

I finally understand this circuit. It is basically a Braitenberg vehicle:

http://en.wikipedia.org/wiki/Braitenberg_vehicles

Given the complexities of matching the gain curves, would it work to use a single module and two antennas that are multiplexed, say, a few times a second? The multiplexing would basically be a switch that would connect first one antenna, get the RSSI, and then connect the other antenna and get the RSSI.

You might need an embedded chip like an ATMega to manage the multiplexing and read the values, but you could also display RSSI as a bar graph:

http://www.rcgroups.com/forums/showthread.php?t=1298192

I don't know much about antennas. Perhaps switching antennas quickly would screw up the receiver?
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