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Old Jan 01, 2013, 07:54 AM
Oxford Panic
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United Kingdom, Oxford
Joined Feb 2003
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Does a tightly focussed tracker ever loose signal when the plane passes overhead so quickly that it can't point accurately? If so I can see the advantage of having diversity with an omni.

A.
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Old Jan 01, 2013, 11:00 AM
Engineer for Christ
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Amherst, VA
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There is no need for diversity when you have a tracker.
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Old Jan 01, 2013, 06:48 PM
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i was just thinking that all the trackers i have seen need a GPS input comeing back from the flying craft to aim the tracker

i was thinking you could use the rssi to do the location info (differential between the 2 side patches)

PS:- i am no electronics person i have read this thread and can only get my head around the most basic parts of it

i didnt even know what rssi was till i started reading this thread

oww and thanks for all your contributions to the RC field IBCrazy
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Old Jan 02, 2013, 07:07 PM
Engineer for Christ
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Amherst, VA
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Check my blog. There's a DIY tracker in there that is RSSI based for you

-Alex
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Old Jan 02, 2013, 07:51 PM
Oxford Panic
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United Kingdom, Oxford
Joined Feb 2003
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The other way to do it is by direction finding using a rotating Doppler array pointing in the direction of the main receiving antenna. I understand this is how full-size aircraft can be tracked by their radio transmissions.

A.
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Old Jan 03, 2013, 02:13 AM
Mobius Cables... I got em'
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United States, TN, Oak Ridge
Joined Dec 2011
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Quote:
Originally Posted by AndyOne View Post
The other way to do it is by direction finding using a rotating Doppler array pointing in the direction of the main receiving antenna. I understand this is how full-size aircraft can be tracked by their radio transmissions.

A.
I think you are overthinking this...

IB will tell you himself... Keep it as simple as possible. You will enjoy the flights more that way. I fly with a Crosshair and a SPW, no tracker, no diversity... I can easily fly miles around me

Diversity was more common before IB and Hugo developed their newer antennas.

Chris
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Old Jan 27, 2013, 05:02 PM
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Romania, Bucharest
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Quote:
Originally Posted by Wadsworth View Post
Turned on both Rx's and the transmitter this time. Both RSSI's are around 4.9v (sorry I didn't mention before that I had positive scaling Rx's and I was running them with the transmitter off).

The selector output goes from 10v to 0v when I switch the Rx channels. Yay! But the video still doesn't switch over from channel two. It just turns into fuz when I switch RX2 to another channel.

On the maxim what is the threshold for the input signal voltage? Mine recieves ~0v when channel two is higher and about 10v when channel 1 is higher. The 10v doesn't seem to be doing the job of triggering the video switch.. But, the video switches when I short it to positive 12v with the saftey bypass switch.

Arrrgh. I'm about ready to call it quits on this thing.
I am in exact the same situation, I've been struggling these days to make the DIY diversity v2 to work. I checked and double checked everything but the damn MAX4547 just won't switch on the another channel. It works only from the manual override switch. In order to clearly test the MAX switching I connected 2 other LED's to pin 2 and 8 and I applied 12V (with a 2k resistor) to the pin 5 (COM1).
I even changed a few MAX chips (I thought I fried something).
The LM chips are working as it should, on the pin 1 of the second LM358 I get 1,2V (not 0V) or 10V, powering accordingly the 2 LED's. The issue is with the video switching. Sometimes this is switching if I touch GND with a metallic screwdriver..that's odd too

IBCrazy, is it ok the 10V command voltage? I read on the MAX4547 datasheet and they say "All digital inputs have 0.8V/2.4V
logic thresholds, ensuring both TTL- and CMOS-logic compatibility ".
Does the second LM358 provide the proper signal for MAX? I mean shouldn't be something with less voltage, like <5V or something (like TTL)?

Thanks!
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Old Jan 27, 2013, 09:59 PM
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Sounds like the threshold is indeed too high. Try turning the gains down on the secondary stage of the Schmitt trigger. You might just use a potentiometer to do this.

-Alex
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Old Jan 28, 2013, 01:38 AM
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As a matter of fact I already tried. I inserted a 5k pot before pin 1 of MAX (as a variable resistor divider) and I crank it at different values. No result unfortunately. I am starting to believe that this v2 schematic (with MAX4547) it is not going to work, this chip expects some specific signal instead of plain DC voltage. On the other hand a HI TTL state means around 2.4V level, right? I got 3V signal using the resistor divider before MAX IC. It didn't work.
A read entire thread and I didn't find anybody who succeeded with this version of the schematic. Everybody started but nobody came up with some field results. I admit that right after I finished assembling the parts on the breadboard I thought it was working. I was fooled by the LED's which were switching correctly. Later I realized that they were the only ones that were switching, the video signal was from a single channel.
I wish there could be a video switch IC that can be used with the resthe circuit (the rest of the schematic works great and it is so simple).

So, anybody... any success story with v2 schematic?
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Old Jan 28, 2013, 04:04 PM
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I have the V2 schematic in my personal unit. Works fine for me. Maybe I miswired something and it worked?

-Alex
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Old Jan 28, 2013, 06:33 PM
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USA
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Quote:
So, anybody... any success story with v2 schematic?
I quickly looked at the V2 schematic in Post #124 and noticed that the MAX4547's logic grounds are missing. If this is the drawing you used then the following pins should be connected to a common ground: 3, 4, 6, 11, 12, 14.

Don't cheat and skip any of these ground pins. Respect them as you would any RF construction and use short lengths on all ground/power wiring. And be sure to include the 10nF capacitor from V+ to ground (see data sheet), soldered in place with very short leads . Skipping little details like this is rarely worth the pennies or time saved.

Keep in mind that the maximum rated voltage for the MAX4547 is 13.0VDC. This is quite close to a fully charged 3S LiPO so it would be ideal to hard limit it to 12V maximum (hint: use a low dropout linear 12V voltage regulator).

Good luck!

- Thomas
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Old Jan 29, 2013, 12:25 AM
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^So I did forget something! I completely forgot that I simply wired the MAX chip per the datasheet and grounded those pins. I still remember talking with you on the phone about this project years ago when I did the V1. My how far we have come since then!

-Alex
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Old Jan 29, 2013, 01:58 AM
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I wired the GND pins, the schematic around MAX was too simple so I studied the datasheet and I connected pins 4, 6, 11, 12, 14 too to the ground. I put even a 10nF cap near the pin 7. But with all these still didn't work. And sometimes the MAX got hot (just as Wadsworth experienced). I use a solderless breadboard so the RF precautions can't be taken enough. Me and a friend of mine checked the circuit so any miswired is excluded.

However, last night I did managed to make it work

I searched the Internet and I found that an opamp used as a comparator will always output less voltage than the power supply by around 2V. And so it was even I powered from 12V or from 5V (desperately I powered form 5V too, I wanted to achieve the TTL threshold required by the MAX IC) I had 10V or 3V on the second LM output.

On the other hand a comparator like LM 393 doesn't have this problem with the lesser output voltage, I bought a few yesterday and put it instead of the second LM. Surprise, the LEDs didn't work anymore (LM393 has open collector output so a pull-up resistor is needed) but the MAX was switching at last, at 12V and 5V. Anyway, I'll stay at 5V as my vRX are integrated on the same board, they are 5.8ghz 5V naked modules used in R305. Besides, at 12V, sometimes, I don't know why, the MAX IC gets hot. So I prefer to stay on the safe side and I lowered the voltage. I even put a Zener diode to limit potentially voltage spikes. Now I have to figure out a way to insert some state indicator LEDs (with some transistors or logic gates). Of course I'll analyse if I have to adjust some resistors for powering everything from 5V.

I noticed that MAX affect a little the video signal that it switches on and off, the video is a fraction duller that the direct connection so I guess a pre video amplifier for both receivers would be useful. As a matter of fact the video signal coming from N01 is brighter than the one that comes from NC1 but I admit is a minor thing that one can live with.
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Old Jan 29, 2013, 02:22 PM
Engineer for Christ
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Amherst, VA
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^I seem to remember messing with the LM393. I had the same results. LEDs no longer worked, but switching worked better. I think I might have used a pull up resistor on the LM358 instead of using the LM393. It has been so long that I cannot remember how I built it. I do remember being frustrated at it, though.

-Alex
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Old Feb 25, 2013, 04:47 AM
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United Kingdom, Sulham
Joined Dec 2010
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Quote:
Originally Posted by futurebreeze View Post
I wired the GND pins, the schematic around MAX was too simple so I studied the datasheet and I connected pins 4, 6, 11, 12, 14 too to the ground. I put even a 10nF cap near the pin 7. But with all these still didn't work. And sometimes the MAX got hot (just as Wadsworth experienced). I use a solderless breadboard so the RF precautions can't be taken enough. Me and a friend of mine checked the circuit so any miswired is excluded.

However, last night I did managed to make it work

I searched the Internet and I found that an opamp used as a comparator will always output less voltage than the power supply by around 2V. And so it was even I powered from 12V or from 5V (desperately I powered form 5V too, I wanted to achieve the TTL threshold required by the MAX IC) I had 10V or 3V on the second LM output.

On the other hand a comparator like LM 393 doesn't have this problem with the lesser output voltage, I bought a few yesterday and put it instead of the second LM. Surprise, the LEDs didn't work anymore (LM393 has open collector output so a pull-up resistor is needed) but the MAX was switching at last, at 12V and 5V. Anyway, I'll stay at 5V as my vRX are integrated on the same board, they are 5.8ghz 5V naked modules used in R305. Besides, at 12V, sometimes, I don't know why, the MAX IC gets hot. So I prefer to stay on the safe side and I lowered the voltage. I even put a Zener diode to limit potentially voltage spikes. Now I have to figure out a way to insert some state indicator LEDs (with some transistors or logic gates). Of course I'll analyse if I have to adjust some resistors for powering everything from 5V.
Futurebreeze

I would like to give this a go using a pair of Rx5808 receivers.
Congratulations on getting it working, are you able to publish the finished circuit for 5v? I have followed the thread, particularly about grounding the appropriate MAX4547 pins, but I am still not quite sure which of the comparators you changed to LM393 and which remained LM358 . I think I will be able to work out the status LEDS with a transistor switch.
Hope you can help
Patrick
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