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Old Jan 03, 2010, 11:46 PM
Fly Big, Low and Slow....
Alpina540's Avatar
USA, VA, Wicomico
Joined Aug 2008
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Quote:
Originally Posted by Alpina540 View Post
Where exactly is the RSSI pin located on the RX? I take it its internal right?

+1 where to buy ...... Digi key?
Wow that was stupid of me I totally missed your post on the RSSI pin sorry...
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Old Jan 03, 2010, 11:55 PM
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subscribed for later... may really read into this
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Old Jan 04, 2010, 08:13 AM
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wedge98's Avatar
East Hartford, CT
Joined Sep 2006
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AWESOME!!! A great tutorial. I plan to buy a few RX's and give this a shot. Well done sir. When I begin the build, I will post everything into this thread
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Old Jan 04, 2010, 08:29 AM
The Flying Circus
ommadawn's Avatar
Adelaide South Australia
Joined Sep 2007
4,032 Posts
I had a quick read of the thread and I guess you are using a comparator cct to switch the strongest Rx signal.

I read the Oracle spiel and they claim:

"Oracle employs a sophisticated real-time video analysis technique. Simply put, the video display is switched to the best receiver based on its video quality. "

Does this seem to compare with your RSS switcher, or are there more smarts happening with the Oracle?

Great thread! I love to see people hacking and building.
Cheers
Frank
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Old Jan 04, 2010, 08:52 AM
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barok's Avatar
Canada, ON, Toronto
Joined Apr 2006
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hi.. please show us a photo of the pcb board with all the electronics soldered on..
thankz..
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Old Jan 04, 2010, 09:47 AM
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wedge98's Avatar
East Hartford, CT
Joined Sep 2006
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Which of these DPDT relay would you suggest to use?

2.95 - 1AMP max - http://www.jameco.com/webapp/wcs/sto...oductId=762030
2.95 - 2AMP max - http://www.jameco.com/webapp/wcs/sto...oductId=187258

I just totalled everything up minus RXs, RX antenna, the voltmeter and 12V battery and cost is $20.67 + shipping from Jameco

Nice
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Old Jan 04, 2010, 10:28 AM
Engineer for Christ
IBCrazy's Avatar
Amherst, VA
Joined Jun 2006
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@Wedge98 - Either will work just fine. The video signal is only a few miliamperes. I would probably opt for the 2Amp unit just because it gives me more room to solder the wires down.

@Ommadawn - This is a bit different than the Oracle system. It switches based on signal strength, not video quality. However, it stands to reason that better video quality follows better signal strength. The good thing about this system is that there is barely any interpretation in the diversity controller.

@barok - Circuit board pictures are coming. I'm out of town for the week. I will take a few pictures when I get back.

-Alex
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Old Jan 04, 2010, 10:55 AM
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wedge98's Avatar
East Hartford, CT
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Thanks Alex.

For those who want to buy it all at Jameco, here's the full list with links:
1 - LM393 voltage comparator (an LM339 works as well and can be found at Radio Shack)
http://www.jameco.com/webapp/wcs/sto...oductId=840000
0.79

1 – LM358 Opamp
http://www.jameco.com/webapp/wcs/sto...oductId=839367
0.99

1 - 12V DPDT relay (I’d get the PC board type, but the automotive type works in a pinch)
2.95 - 2AMP max - http://www.jameco.com/webapp/wcs/sto...oductId=187258

1 - RCA cable
http://www.jameco.com/webapp/wcs/sto...ductId=1949470
0.95

1 - RCA female output jack
http://www.jameco.com/webapp/wcs/sto...ductId=1766091
3.55

1 - UA 7805 voltage regulator
http://www.jameco.com/webapp/wcs/sto...gDrillDownView
0.69

1 - pcb board (2”X4” is sufficient if you are decent at packing electronics)
http://www.jameco.com/webapp/wcs/sto...oductId=169279
2.95

3 - 10K resistors (1/4 Watt)
http://www.jameco.com/webapp/wcs/sto...ductId=1867634
3 x 0.03 = 0.09

1 - 2K resistor (1/4 Watt)
http://www.jameco.com/webapp/wcs/sto...ductId=1867896
0.03

1 - NPN transistor (2n2222A, BC547C, or similar)
http://www.jameco.com/webapp/wcs/sto...roductId=38236
0.45

2 - 47uF Capacitors
http://www.jameco.com/webapp/wcs/sto...oductId=546100
2 x 1.25 = 2.50

1 – 100K potentiometer
http://www.jameco.com/webapp/wcs/sto...roductId=29103
1.09

For the system:
2 - video receivers
2 - Video antennas (I used 2 patch antennas, but you can use Yagis, Patches, Omin directional dipoles, or any mix)

A 12V battery

Optional Parts:

Voltage monitor or volt meter

Power switch
http://www.jameco.com/webapp/wcs/sto...oductId=158078
1.29

Red LED/green LEDs
Green:
http://www.jameco.com/webapp/wcs/sto...oductId=697661
0.08
Red:
http://www.jameco.com/webapp/wcs/sto...oductId=697611
0.09

2 – 100k multi turn potentiometers
http://www.jameco.com/webapp/wcs/sto...roductId=29103
2 x 1.09 = 2.18

Total Cost:
0.79 + 0.99 + 2.95 + 0.95 + 3.55 + 0.69 + 2.95 + 0.09 + 0.03 + 0.45 + 2.50 + 1.09 + 1.29 + 0.08 + 0.09 + 2.18
$20.67
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Old Jan 04, 2010, 08:18 PM
Engineer for Christ
IBCrazy's Avatar
Amherst, VA
Joined Jun 2006
10,567 Posts
Excellent post Wedge. I don't know about the PCB board though. It's a lot of drilling to drill out that one. I prefer this Pefrorated board

I also prefer these potentiometers: 100K cermet trimmer

I also forgot that in the optional parts you need 2 390 ohm resistors for the LEDs: 390 ohm resistor

I'd also use these capacitors (they're cheaper): 47uF electrolytic capacitor

-Alex
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Old Jan 05, 2010, 01:05 AM
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I'm subscribing to this, looks useful.
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Old Jan 14, 2010, 01:00 PM
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Hi IBCrazy,

Now that you've had your diversity for awhile, how do you like the performance?

Thanks,

-Patrick
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Old Jan 14, 2010, 01:10 PM
How do I change this text?
Darth_Elevator's Avatar
The Beautiful Mountains of Utah
Joined Oct 2006
6,232 Posts
Alex, thanks for a great thread. For $20 bucks worth of parts and a few hours of my time, I can hear this sweet little project calling my name.
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Old Jan 14, 2010, 07:02 PM
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Ireland
Joined Apr 2001
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i like the idea of useing the rssi signal but the relay is a bit too primitive in my opinion.
Who knowsw a "solid state" way of switching ?
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Old Jan 14, 2010, 08:28 PM
Engineer for Christ
IBCrazy's Avatar
Amherst, VA
Joined Jun 2006
10,567 Posts
cmulder - Use a solid state relay or a video switch. I chose a relay since it's life is well beyond what I'll ever use. It also give the best video quality with the least distortion.


The system works very well for me. I have a Comtech modules, which the RSSI voltage is proportional to the log of the signal strength and drops near zero at no signal. It really works great with this. I have dropped my potentiometer to about half for best performance.

For the inverted signal, the switching is a little harder to tweak and in most cases you'll run the potentiometer all the way up to max resistance or you can just cut it out of the circuit all together. This means it will switch a little more often, that's all. It won't affect performance. However, you can change the direction of the signal and get a non inverting RSSI signal by using an LF412 OpAmp and an extra battery (the LF412 requires a negative voltage to work). What you need is to place the LF412 in the inverting buffer configuration (the exact same as the LM358 buffer, but you just reverse the inputs at the inverting and non inverting terminals). Then you need to place a fixed voltage on the LM358 buffer to act as an adder to get the signal positive voltage. You can use the 5V from the voltage regulator for this and a 10 K resistor on the 5V and the output of the LF412 to make the adder. In my opinion, I'd just use video switch in place of the relay instead and turn the potentiometer all the way up.

If someone wants the signal inverter circuit described above, I can draw it up.

Perhaps MartinY can recommend a video switch IC which will work in place of the relay? It sure as heck would be easier than building the signal inverter. I would think the ba7654 would work fine. Rohm.com sells them. The TS5a4624 from Texas Instruments would also work.

-Alex
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Last edited by IBCrazy; Jan 14, 2010 at 10:02 PM.
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Old Jan 15, 2010, 01:13 AM
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Romania, Dolj, Craiova
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Or maxim chips, they send samples for free
http://www.maxim-ic.com/app-notes/index.mvp/id/3823
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