isk

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OPLink signal range - Revo vs Mini
« on: April 13, 2017, 07:04:15 pm »
Hi, first post here. I'm trying to get OPLink running between a Revo and a Mini without much success

I set everything according to the docs with the Revo as receiver and the mini as coordinator and connected to a PC running GCS 16.09. Flash erased both and installed firmware, set everything in the config, and binding was successfull and I get wireless telemetry. The only problem is, the connection is only active when the devices are about 10cm apart, any further apart and the signal drops.

I always have the stock antennas connected on power up and only set the power > 0 when testing. I tried with two separate minis but same problem. Is this a problem with the OPLink antenna on the Revo? Or have I missed something blindingly obvious?

Thanks, Ian   

Brian

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Re: OPLink signal range - Revo vs Mini
« Reply #1 on: April 13, 2017, 07:23:37 pm »
It is likely the OPLink.  Where did you get you OPLink from?  There have been problems with clone OPLinks having short on the antenna, which (of course) greatly reduces the power/range.

If you have a multimeter, please test the resistance between the center pin of the antenna connector and ground (all of the other pins on the connector are ground).  If it's very close to zero, you have a bad OPLink.

isk

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Re: OPLink signal range - Revo vs Mini
« Reply #2 on: April 13, 2017, 08:38:20 pm »
Hi Brian, I got them both from RadioC, the product link is https://www.radioc.co.uk/ProductDetails.asp?ProductCode=3116-1. I checked the resistance as suggested and get 0.6 ohms and 0.8 ohms respectively. I guess that's pretty close to 0? Thanks

Brian

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Re: OPLink signal range - Revo vs Mini
« Reply #3 on: April 13, 2017, 09:03:58 pm »
Yes.  That's not good.

The problem is that there is insufficient clearance between the center pin of the antenna and the inner ground plane.  If the manufacturer tolerances are not good enough, the antenna pin shorts.

We were actually able to track down one manufacturer and told him about this, and he said he would fix it, but there could be other manufacturers, or these could be from the older batch.

In any case, the only fix is to de-solder the antenna connector and drill out the center hole with a very small drill bit to break the short.  You will not be able to put the antenna connector back on after this, but you can solder a wire antenna directly onto the RFM22B module.  I have done that on a couple of moudles, but you probably will want to talk to the re-seller and see if you can send them back.

isk

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Re: OPLink signal range - Revo vs Mini
« Reply #4 on: April 13, 2017, 10:16:09 pm »
Thanks again Brian, I did a bit of Google research and see now that this is a common problem. I emailed the reseller but don't expect a response until next week. Frankly, for the price and limited availability of these things, I might have a crack at the mod as you've suggested. Soldering a wire antenna onto the RFM22B seems achievable but I wouldn't know which wire to use or pins to solder. Can I chop and wire the MMCX end of the SMA pigtail that came with it?

Failing that, is there a reputable supplier selling working modules out there?

Thanks. 

f5soh

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Re: OPLink signal range - Revo vs Mini
« Reply #5 on: April 13, 2017, 10:49:50 pm »
Take a look here:
https://forum.librepilot.org/index.php?topic=312.msg18007#msg18007

And a few post before for cutting pcb trace.

Brian

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Re: OPLink signal range - Revo vs Mini
« Reply #6 on: April 13, 2017, 10:54:16 pm »
I don't know of any supplier that is known to have good ones.  I haven't bought any in a while.

Any small gauge standard wire will work.  I like using something like 24 gauge silicon wire, which is flexible.  You just need to solder it onto the first pin of the rfm22b next to the antenna connector, and cut it to ~173mm in length.

isk

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Re: OPLink signal range - Revo vs Mini
« Reply #7 on: April 14, 2017, 12:51:52 am »
Thank you both for the advice and guidance. I went ahead and made the mod with promising results. I'll do a full range test tomorrow but for now I get a really good telemetry signal at about 30m. I'll mod the other one later. I have attached an image of my work. Cheers  :D

Re: OPLink signal range - Revo vs Mini
« Reply #8 on: April 14, 2017, 08:48:33 am »
For anyone else looking for OpLinks, about 2 months ago I bought one of these and it was perfect (all working and frequency correct).  Of course they printed my review because it was favorable:
http://www.xt-xinte.com/F16086.html

I also bought a second of these (OpLink with case with SMA) and the USB connector had to be resoldered this time (perfect a year or two ago).  I like the SMA connectors.  I have watched this link for a while, and the review numbers don't add up.  I now have two sets, and thus two "OpLink Air" that I can't use except if I ever burn an RFM22B (I haven't ever so far).
http://www.xt-xinte.com/F17009.html

They also have Sparky2's for about $39 shipped.  I bought 2 years ago and 2 months ago and both needed power jumper resoldering, and rf connector solder blob removal.  Good baros.  Again review numbers are complete lies, they have a 1 star, a 3 star and a 5 star review averaging out to 4.5   Go figure (standard overseas lies).
http://www.xt-xinte.com/F16821.html

These Sparky2's (about $50 shipped) are the real authentic black ones that aren't sold any more.  Probably the last of the authentic stock.  They appeared after the official seller (hobbiesfly) stopped selling them.  I bought 2, two months ago.  Perfect in all regards.
http://www.ebay.com/itm/Taulabs-Sparky-2-0-32bit-F4-MCU-Based-Flight-Controller-compatiable-Librepilot-/172353561802

I guess I have been lucky because all the RFM22B stuff (10?) I have bought in the last couple years (most recent purchases 2 months ago) has been good (no shorts and correct frequency) except for the one USB connector that had to be resoldered.  (I have an uncrashed authentic Nano that needed USB resoldered when it just popped off one day.  I blame ROHS solder.)

startrek66

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Re: OPLink signal range - Revo vs Mini
« Reply #9 on: October 10, 2018, 01:03:06 pm »
Hi guys. A question about the range of signal reception. With the classic antennas that are sold that distance of reception should be expected based on the transmission powers?

Re: OPLink signal range - Revo vs Mini
« Reply #10 on: October 10, 2018, 06:03:20 pm »
All max ranges assume 100mw setting.  1/4 the power goes 1/2 as far (e.g. 25mw goes half as far as 100mw), so you can figure out ranges for lower power levels.  1/64th the power goes 1/8th as far.

Any one with similar or different experiences please post.  :)

There are reports of 7km on other omnidirectional antennas.  This was probably under ideal conditions and should not be expected.  I've gotten easily 2km on other good antennas (at 100mw ... that translates to about 250m at 1.6mW) without doing any of the extended range things:
- mounting the base station antenna on a pole
- directional base station antenna
- flying at a high angle above base
but doing the minimum:
- both antennas vertical
- aircraft always high enough to be in line of sight

Beware that simply banking the aircraft can cause loss of reception when at long range.  This is an antenna polarization issue.  Two antennas like this | | work well but like this | _ do not work well.

The wire dipole antennas that come with OpLinks and Revos are good antennas if configured and mounted correctly.  I would put their performance as about as good as you will get.  These wire dipoles should be mounted like ---| with the dashes being the coax coming out sideways and the two wires being vertical (one up, one down).  A ferrite bead on the coax at the antenna wire junction probably helps.

Here is a post I did testing many antennas:
https://forum.librepilot.org/index.php?topic=4199.msg28510;topicseen#msg28510

My guess is that anyone who has decent antennas mounted/held correctly can hope for 2km LOS when both antennas are vertical but your RF environment may be different (noisy):  You really really should either:
- have a working failsafe RTB
- fly with base antenna held in a non-optimal way (low or pointing toward the aircraft) so that when it goes out of range you can just raise the transmitter above your head with antenna vertical and know you can get control back.

You should also fly in attitude mode.  Loss of FPV vision or RC control when banking in Rate mode will cause a crash.

Careful base station antenna mounting (high and clear of obstruction) and you might get 4km, but you should assume it will fail at any time until proven otherwise.  Again, RTB should be considered a requirement.

Experts can replace the RFM22B with an RFM23BP (requires soldering rework station, expert soldering, electronics knowledge to add an additional clean 5.5V or 6V power supply for only the RFM23BP, possibly additional licensing depending on your country) which runs at basically 1000mW only until you measure/verify the lower power settings (which for the RFM23BP are undefined).  There is a reason those lower power levels are undefined (the amplifier design doesn't throttle well/cleanly).

Be careful of switching power supplies, such as switching BECs.  They can produce a lot of RF noise and greatly affect range.  I had an issue before, so now I run linear BECs or at least test.  The 3rd harmonic of 433 is 1299, which is really close to 1280.  433 will affect 1280 FPV reception on the ground (but 1280 shouldn't hurt 433).

Test test test.  Use min power for tests.  Do not set it on the ground for a test.  Keep metal away.  Turn things off (fpv cameras sometimes have switching regulators) or use linear power supplies for the test to see what range you can get with accessories on/off and using linear/switching power supplies.  I get hundreds of meters on 1.6mW.  When you get that your antennas are good and your noise level is good.

startrek66

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Re: OPLink signal range - Revo vs Mini
« Reply #11 on: October 11, 2018, 05:25:07 pm »
great you are a mine of information! I read that to check the quality of the oplink module, just measure with a Ohm Etro the resistance between the central and the ground of the antenna connector. is it enough and safe?

Re: OPLink signal range - Revo vs Mini
« Reply #12 on: October 11, 2018, 05:37:36 pm »
Some outputs are shorted out.

Measure with an Ohm meter.  It should show as an open circuit (no connection) because it is capacitively coupled.  There are reports of successful repairs where a trace was cut before the short and a cable with connector was soldered on, center conductor soldered upstream of the cut and cable shield soldered to ground.