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oxxyfx

Using RSSI signal for Patch antenna positioning

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Hello,

I was thinking today - on a possibility to use the RSSI signal coming out of the receiver to rotate the Patch antenna so it sort of follows the plane.

The ideea came from reading several posts on this forum, I know this already has been done, and I seek the advice of those who have done it.

I have the Airwave 623 receiver, and it has an RSSI output pin (7). I put it on my scope today, and started measuring, checking the signal levels, but I am a little confused - perhaps because of my lack of understanding this signal.

From all I've read, the RSSI should give us a DC signal, which increases when the transmitter is closer and decreases when the signal level decreases.

I thought about introducing this signal into a PIC comparator module and on one of the PIC output pins to generate a servo signal, which will rotate the servo left or right depending if the signal is getting stronger or lower.

Now, so far what I've seen on the scope is the following:

1. I turned on the receiver with no transmitter on nearby - (however I have a wifi router and a 2.4 Ghz phone working in the house) and the RSSI shows me about 3.4-3.7V DC signal.

2. I turn on the transmitter right beside me, the RSSI signal drops to 0.5-0.7V DC.

Am I missing something here, or this is working exactly in the reverse as it should?

Please let me know what I am doing wrong. A regular voltmeter confirmed the above values, since I didn't see to get anywhere with the scope, I verified the values with the regular Voltmeter.

Thanks,

Ox.

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So is the idea workable? Can I just simply bring that signal into a PIC's comparator module, and in function of the signal level try to manipulate a servo on the output?

Or do I need to modify the signal for (ex. invert it) before I bring it in?

Thanks,

Ox.

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Thanks Terry,

I spent quite a bit of time today reading that thread. It is a great thread, and based on that I am not sure any more if it would be worht doing this with a servo or not. I've been thinking of a single PIC solution which would read the rssi, compare it to a preset , and if it is higher - than go and move the servo.

If the servo is center, and not been moved before, move it right 5 degrees, check signal, if it is above previou stay, store success in a variable. If if is lower, store failed in a variable, move left 10 degrees, check signal, if it is better than compare it againt the one before the movement to see if it is better than that or not. If it is not store failed in a variable, move another 5 degrees in the same direction. If it is, stay, store success in a variable.(I hope you can follow me... :))

and so on, there are several scenarios here.

Also I would drive the servo with PIC signal, stretching the pulses to allow nead 170 degree rotation, I would probably not need more, since my club does not allow me to fly behind the flight line anyway.

However seeing your website, reading the thread I was also thinking about the 3-4 receiver solution where we switch to the one with the strongest signal - the only backdraw for this, is that it would require a powerouse to keep all 4 receivers under power all the time...

Thanks,

Ox.

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If the servo is center, and not been moved before, move it right 5 degrees, check signal, if it is above previou stay, store success in a variable. If if is lower, store failed in a variable, move left 10 degrees, check signal, if it is better than compare it againt the one before the movement to see if it is better than that or not. If it is not store failed in a variable, move another 5 degrees in the same direction. If it is, stay, store success in a variable.(I hope you can follow me... )

Yep, thats how mine works. The only other thing is to take multiple signal checks each time or the aerial movement gets very jumpy due to odd dips in the signal. It only take a blip as you test the RSSI and the aerial will move the wrong way. There is a balance to be made, how long you test for v speed of tracking. Long range tracking is easy as tracking speed dose not need to be high which also suits your servo idea.

Your right about the 4 receiver system eating power though, mine pulls around 1A. The upside is it never looses track of your plane even if you buzz the aerials or do loop the loop round them.

Terry

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Thanks Terry.

In case of the 4 receiver system, what kid of circuit do you use to switch between video signals? can that be done with a PIC, or it needs a special signal processor?

Thanks,

Ox.

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Yes I use a PIC ( 16f818 ) as the brain. 12f508 and LM1881 on each rx to detect the valid video and an LM6574 to switch the video.

Terry

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Terry,

in another thread I've seen here you said that when switching from one receiver to another you can see horizontal lines on the picture - I cannot recall exactly your terms.

Do you switch the receiver during the v-sync signal? If you don't can these lines be eliminated if you would switch the receiver while this v-sync occurs?

I am just thinking one thing here, how can one make sure that the 4 video signas coming from each of the receivers are in sync with each other? Because it these are not, then the v-sync on one receiver does not occur the same time as on the other....

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how can one make sure that the 4 video signas coming from each of the receivers are in sync with each other? Because it these are not, then the v-sync on one receiver does not occur the same time as on the other....

I was also thinking about the same thing recently. And it struck me one day just after I woke up. They will always be in sync, because they receive the same signal and all sync to it.

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Do you switch the receiver during the v-sync signal? If you don't can these lines be eliminated if you would switch the receiver while this v-sync occurs?

No I don't. I use my video link to allow me to fly to, take still pictures of a target and then fly back and land. Switching lines or minor drop outs are not a problem to me as I don't use the feed to make movies. This is one reason I have not shared my code, most users seem to want to make movies so it would not be suitable for them. Having said that, it is only a big problem when indoors, when outdoors very little switching goes on.

I think the lines could be eliminated but it's not an issue for me.

Terry

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