sv2fpv

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OpLink mini rf amplifier
« on: June 30, 2017, 08:28:20 pm »
Hi
My question, can connect unidirectional rf amplifier on OpLink mini?
Setting OpLink mini only control ppm as coordinator
Setting Revo only control ppm as Receiver
Is that right to work?

Re: OpLink mini rf amplifier
« Reply #1 on: June 30, 2017, 09:21:37 pm »
I think that is correct; that in this case the receiver does not send acknowledgements.

Of course you can test this.  Set both ends to say 1mw and determine the range.  Then set just the transmitter end to a much higher power and make sure the range significantly increases.

sv2fpv

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Re: OpLink mini rf amplifier
« Reply #2 on: June 30, 2017, 10:15:32 pm »
"I think that is correct; that in this case the receiver does not send acknowledgements" I don't know if that is sure.
Tested with 7 watt amplifier
At 100mw in, out is 6 watt.
Not flying tested but in range of 50meter
100mw = 9 +20 on Gcs
6watt = 9 +60 on Gcs

Thanks

Re: OpLink mini rf amplifier
« Reply #3 on: June 30, 2017, 10:40:15 pm »
The question is whether the receiver sends acknowledgements back.  Just measuring the received power doesn't answer that question.

If you test like I suggest, you can be sure that you don't need to increase power on the receiver as well.  I am almost certain that you don't need to increase power on the receiver for the setup you discribe, but this is a way to test any system.

I get about 300m at 1.6mw with omni antennas.  That is 2-3 km at 100mw.

Re: OpLink mini rf amplifier
« Reply #4 on: June 30, 2017, 10:46:40 pm »
(It wouldn't let me edit the previous message.)

It is important to have good antenna systems, especially at high power.  Interference can be a real problem even at 100mw.

sv2fpv

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Re: OpLink mini rf amplifier
« Reply #5 on: June 30, 2017, 11:15:23 pm »
 interference have at 6watt but at 3-4 watt is ok, tested with stock antenna, next step with custom antenna.
Oh i don't believe that 1.6 mw 300 meters data transfer.

Anyway thanks

Re: OpLink mini rf amplifier
« Reply #6 on: June 30, 2017, 11:53:33 pm »
I have good omni antennas and a flight log to back it up.  I will try to dig it up and post it here.

Edit:
Here is a screen capture of the logged flight.  For this flight, the max distance was more like 260 meters (don't forget to calculate as sqrt(x^2+y^2+z^2)), but it also was never out of range, even with all the stunts I did that flight.  It did have some dropped packets.  At the end of the flight, you can see where I disconnected the flight battery; the RSSI went to -127 and RxGood went to 0 just before I stopped logging, yet it was better than that the whole flight.  When the link is completely lost RSSI goes to -127 and RxGood goes to 0.

This is with vertically oriented linearly polarized omni antennas.  I used a Nagoya 771 on the ground and a Nagoya 701 in the air (didn't even have ferrite beads).  These are not ideal because they really need a ground plane / counterpoise.  Simple dipoles like the stock OP antenna would be better than these.

Home was in the center of the runway, but the GCS/OpLink was off to the side of the runway.  I was flying mainly up and down the runway and on the far side of the runway and the actual distances would be slightly farther than logged.

Screen cap shows x, y, z distances from Home, OpLink RSSI, OpLink RxGood (number of good packets in last 64 packets).

« Last Edit: July 01, 2017, 05:41:48 am by TheOtherCliff »

Brian

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Re: OpLink mini rf amplifier
« Reply #7 on: July 01, 2017, 12:47:23 am »
If the radios are configured for control only, then that is unidirectional.  Acks are not used in either case, and I'm pretty sure that, even in the bi-directional case, control information will always be received correctly as long as the Rx can receive from the Tx, but, of course, no data can be sent the other direction.

That said, what country are you in?  Most regions have restrictions on 433 MHz that limit the power used, and you really shouldn't need more that a watt.

sv2fpv

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Re: OpLink mini rf amplifier
« Reply #8 on: July 01, 2017, 09:20:09 am »
Thanks
Maybe have interference from amateur radio repeaters
Amateur radio band 430-440 mhz
Flight test, 3 watt next days.

Have a good day.

f5soh

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Re: OpLink mini rf amplifier
« Reply #9 on: July 01, 2017, 11:55:18 am »
The Ham radio 70cm band is indeed 430-440Mhz but you should take in account the IARU band plan, especially using this power levels:
https://www.iaru-r1.org/index.php/spectrum-and-band-plans/uhf/70-centimeter

Avoiding repeater inputs and sat up link, configured channels 85-124 (433.400-434.960Mhz) will be a good candidate.

sv2fpv

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Re: OpLink mini rf amplifier
« Reply #10 on: July 01, 2017, 02:03:46 pm »
Yes that is my choice, more wide 50 - 150
Repeaters have very strong signals in all open area in the town
About 437-439 rx tx
About 431-434 rx tx
426 - 427 tetra(dataVoiceRepeater)very strong signal

Next days testing with custom antenna and 3 watt tx, 85-124 channels

Please tell me if that is right "If the radios are configured for control only, then that is unidirectional.  Acks are not used in either case"

Thanks for all answers

Brian

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Re: OpLink mini rf amplifier
« Reply #11 on: July 01, 2017, 05:23:06 pm »
Read my post above.  ACKs are not used in any case.

Re: OpLink mini rf amplifier
« Reply #12 on: July 01, 2017, 06:00:48 pm »
Isn't it more accurate to say that Acks are used with some forms of telemetry, but never with "control only"?

Also, for long range unidirectional "telemetry only" you may want to try setting the model as Coordinator and making it's transmit power be the higher one.  This may or may not work well as the high priority coordinator task can fight with with the high priority stabilization task for time critical CPU access.  Is this task priority issue tracked to be worked on?

sv2fpv

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Re: OpLink mini rf amplifier
« Reply #13 on: July 01, 2017, 08:22:06 pm »
Ok Brian i understand it, it does not have ack, thanks.

Oh Cliff thanks  i understand it.
 I do not want the telemetry, but I can try it, with another receiver(2.4ghz) for control.

All working fine
osd = ok
only control(3watt TX) = ok (not tested in flight range)
very good position Hold

Little problem with the compass, oscillating in gps mode in all directions

Thanks

Re: OpLink mini rf amplifier
« Reply #14 on: July 01, 2017, 08:56:07 pm »
Is the compass oscillating or is the vehicle oscillating or both?

You really need an external compass and still must carefully twist all power (high current) cables.

There is also a different GPS oscillation issue that happens with some DJI/Naza GPS/compass.
https://forum.librepilot.org/index.php?topic=3012.msg21154#msg21154