[karla]

Hello all,
I would like to reach out and hear your experience / expectations about the range before failsafe (not stretch range but your comfort zone) when using OPlink as a control channel on 433 mHz using the max 0.1 watt power (100 mW).
Lets assume you stand on ground and vehicle is out over sea.
Also assume you use these antennas on both transmitting and receiving units (hope pic uploads ok)

. 100 m
. 1.000m
. 10.000m
. Anything in between or beyond?

For me I would expect a range longer than any 5.8 Ghz video link can provide, even with a tracker.
But I don't experience that.
Whats your experience?

(I am just assuming there should be no major difference in range if you are using the built in receiver on the revolution board?)

[jdl]

My personal expirience:

RMILEC 433MHz SRC771 Dipole on OPLINK Transmitter (Ground):



433MHz Whip monopole antenna: (on Carbon Frame ZMR250):



Using Revo built-in receiver, running 57600bps control & telemetry, 100mW TX power.

Flying at height 150-200 meters above ground, almost never had problems before 3km. Once got failsafe at 3300+ meters (RF interference), and my record is 3500-3600 meters distance, not bad for ZMR250 frame with a HD camera on it (5200mAh battery ). I think 4km is absolutely achievable and 5km is marginally possible distance (without almost any spare juice left in the battery after return), but these limitations come from the frame, not from the OPLINK Radio.

But, if flying 1-2 meters above ground, I usually lose contact and FS is triggered at about 600-800 meters distance.

[chromvis]

I had significant problems even within 10 m, but this did not seem to be transmission problems but rather signal processing.
I was using this Remilec antenna and various types of antennas on revolution. System was set for Data and Control with 57600 baud for telemetry. I modify my TX, connect OpLink to trainer port for PPM and to GCS via USB. Before I was trying to use Bluetooth for telemetry transmission to computer, but it seems to jam everything within 5 m.
With this setup everything works fine in general. I did walk test for up to 500 m in the forest and behind houses RSSI was falling to -80 or 90 dB but control still works. What force me to abandon this form of copter control is occasional sudden loss of signal forcing copter to literally fall form the sky. It happens about 6 - 7 times within last 6 month with different setups (I have 5 Revolution FCs and 2 Sparky2 and I was testing different configurations). I noticed a couple of times that when it happens GCS show -128 dB signal (complete loss of a signal) it usually recover within 2 to 5 sec, but copter already grounded. So, I decided it will be safer to install receiver in S.Bus mode (never had problems with it) and use OpLink only for telemetry and things like mag calibration or checking vibration values after autotune etc.

[hwh]

The "expected" or design range is more what jdl is experiencing, good long range.

Unfortunately the quality of the oplinks coming from China varies a great deal.  Some are good, some are almost dead and only reach a few tens of meters.  Some even have the antenna center pin shorted to the ground and only reach a few meters.  Others use clone RFM22b modules that are way off frequency and won't connect to one that's correct.

[karla]

Thanks a lot idl, chromvis and hwh!
That was three really different answers and all very useful.

I noticed a couple of times that when it happens GCS show -128 dB signal (complete loss of a signal)

Regarding the Link Meter in the GCS, Is it a reliable source of the actual control signal (using PPM and telemetry 57K speed)?
Do you have any explanation to the scale of the Link meter, How to read it?
beyond red is bad and green is good

[f5soh]

Do you have any explanation to the scale of the Link meter, How to read it?

This show the signal strength according to classic S-Meter specifications:
https://en.wikipedia.org/wiki/S_meter

S1 is -121dBm
S2 is -115dBm, etc.

[zzaphod]

Thank God I thought I was going mad!!

The quality issue is a pain, I have been sent two OPLM modules and two revo's by my supplier so far and although they will bind and work the range on both occasions has only been a few meters, 10 Meters at very best, so this time I got myself an RF meter 

The Revo is putting out 84Mw but the OPLM is reading 0mw, I checked continuity etc before returning the OPLM AGAIN, the supplier has emailed me to say they have tested it and it is working and attached a screen shot showing the link at -64bB  with the OPLM and Revo side by side 

WOW think I need to change supplier!!!!!
 

[hwh]

Some of the OPLM from China have a defect, the center pin of the connector is shorted to ground on the inner pcb layer.  There's another thread that explains how to check and fix them.  To check them you just check what the resistance is between the antenna connector center pin and ground.  Anything other than open is bad.  The thread https://forum.librepilot.org/index.php?topic=312.msg17951#msg17951 discusses this and how to fix them.

[zzaphod]

Some of the OPLM from China have a defect, the center pin of the connector is shorted to ground on the inner pcb layer.  There's another thread that explains how to check and fix them.  To check them you just check what the resistance is between the antenna connector center pin and ground.  Anything other than open is bad.  The thread https://forum.librepilot.org/index.php?topic=312.msg17951#msg17951 discusses this and how to fix them.

I did check continuity on the first one I returned and there was a reading where as the revo was open, at the time I did not have my RF meter but assumed it should be open LOL. Thanks for this info, just wish I had found it earlier, shop just say they have tested and cannot find a fault as it does pair up, I have replied telling them to move the Revo and OPLM ten meters apart then they will see the problem.

[hwh]

You could send them a link to the thread I mentioned. 

The "defect" was in the original oplinks as well, the clearance on that inner layer is really too small.  If you have the PCBs made by a company that does a really good job (the original OpenPilot apparently did) it works OK.  If the PCB house tolerances are a little looser you end up with boards that are shorted.

[xfce]

Do you have any explanation to the scale of the Link meter, How to read it?

This show the signal strength according to classic S-Meter specifications:
https://en.wikipedia.org/wiki/S_meter

S1 is -121dBm
S2 is -115dBm, etc.

you said is for HF
it seems for 433MHz(UHF), S1 is -141dBm, S2 is -135dBm.

[karla]

You could send them a link to the thread I mentioned. 

I actually did send the link to my two suppliers who each send me 2 shorted OPLM. I have not got any answer yet after a week. As I have mentioned before these two suppliers sell on all the major platforms AliExpress, Banggood, DHgate, ThanksBuyer, eBay etc. Platforms differ but products are the same. I keep chasing them, meanwhile I am repairing the boards with the kind help of people in this forum. I don't think they should be left keep on doing what they are doing without being noticed.

[hwh]

It's hard to detect whether an oplink available on a website is the defective one or a good one.

One thing I've noticed is that the ones that the Chinese laid out the board in a slightly different design don't usually have the problem with the shorted antenna.  The defective ones are the ones that are an exact copy of the original oplink.

I've switched to buying the ones that have been redesigned to have a SMA connector on them.  I prefer the larger connector anyway.

[f5soh]

you said is for HF
it seems for 433MHz(UHF), S1 is -141dBm, S2 is -135dBm.

I do not known this scale.
This "UHF scale" do not make sense assuming the RFM22 noise floor mentionned in doc  is -121dBm.
Same for Rssi range: