Ground OpLink is always 50mw.  I increase air Revo RF power from 1.6mw to 50mw and get much less range.  That's wrong.  Details that follow seem to me to prove that Revo has much less range (both Tx and Rx !!!) when set to 50mw and much better range when set to 1.6mw.  OK, 50mw somehow messes up the transmission (telemetry going back to GCS), but why would it mess up reception (RC Control signal from OpLink to Revo) ?? ??   I have not tested other power settings.

I have verified this issue with two different models and two different (authentic OP) Revos.

Details:

I have an old FW FPV rig using 72mhz for control and Revo(air)/Oplink(ground) "telemetry only" that I flew to about 2km with telemetry still working most of the time at 2km.  GCS is 50mw and aircraft is 1.6mw because high power in the aircraft seems to mess with the Futaba PCM 72mhz RC rig.  Still not certain about that because RC problems at high power seem to still happen even with GCS OpLink powered off (so the aircraft Revo should never transmit).  GCS OpLink is coordinator.  Both links are set to "telemetry only".

I have a new FW FPV rig using Revo (50mw) with OpLink (50mw) for control and a base station with RC receiver sending PPM to OpLink currently connected via USB, although there is a bluetooth adapter connected that I have not had time to get working.  GCS OpLink is coordinator.  Both links are set to "control and telemetry".

I assumed that frequency drift was the problem, but before going there, I wanted to recreate the issue.  I did.  I also did some mix and match.  Using same (new) GCS OpLink, always set to 50mw, the old fixed wing Revo got good ground range at 1.6mw (several hundred meters and didn't try farther) and bad ground range at 50mw (hard range limit hit at about 100m and walked around for a while at several hundred meters and got zero telemetry packets received.

The PPM outbound link at 50mw(air) and 50mw(ground) has the same range issue as the inbound telemetry link because it ran out of range solid hard at 200-300m with good antenna alignment and perfect LOS and no RF reflective stuff in the environment.

The one experiment was at the flying field and the other was in my subdivision, so two different locations with same results.

Using good Nagoya antennas.  The long one on the base and the short one in the aircraft.  The new aircraft has a ferrite bead at the antenna end of the RF cable.

Both Revos are old originals from OP days.  I think one OpLink is new China stuff but the other is OP from Kevin Finisterre's store.  But again, I can't see any difference caused by OpLinks.

Given that the OpLink is running 50mw in all cases and the Revo works well at 1.6mw but not at 50mw it seems to be a Revo hardware issue since I have a hard time imagining a software issue that won't work just because it is 50mw.  I don't think it is an AGC recovery issue with the Revo because it seems that the Revo never transmits.

What could cause both issues?
 - Revo (non-coordinator) isn't supposed to transmit with base station (coordinator) OpLink powered off but the 72mhz RC fails if Revo is set to high power even when GCS OpLink is powered off
 - Configuring (authentic) Revo to send at 50mw causes both Control reception and Data transmission to fail.

I wonder if old OP release works better than this; the one where the Revo RF task had a higher priority.  Hmmm an RF echo at high power causes a 0 byte reception and the last good receive packet is parsed again....

I have a Nano with an OpLink that I will test to see if OpLink to OpLink can work at 50mw and 50mw.  (Update:  Nano + OpLink works much better than either of these two authentic Revos).

I can also look at the noise floor to see if the Revo is generating noise when set to 50mw.
« Last Edit: November 20, 2017, 06:16:52 am by TheOtherCliff »

Nano with OpLink telemetry at 50mw had much better connectivity than any previous test.  It appears that the OpLink is working as specified at 50mw and Revo is not working well at 50mw.

I used the same GCS rig, same antenna location, same ground OpLink, same power as all other tests I did today.  I used the air antenna (short Nagoya) that does well with [email protected] but does poorly with [email protected]

I noticed that the signal level at the GCS was about -23dbm with Nano + OpLink in warmup location.  It was in the -40's for Revos with the same aircraft warmup location.  Everything at 50mw.  This alone says there is something very much different with Nano+Oplink in aircraft vs. Revo in aircraft, both set to 50mw.

Conclusion is that OpLink RF works correctly but Revo RF does not.

A good test would be to measure current at each power level (while transmitting a lot).  It won't be conclusive in that low current does not necessarily mean that low power is being requested by the code, but high current at high power setting will at least suggest that the code is asking for high power.
« Last Edit: November 19, 2017, 04:53:20 am by TheOtherCliff »

Can anyone recreate this?

f5soh

  • *****
  • 4363
    • LibrePilot
No, at least here.  :o
Power levels measured at output are as expected while changing setting from 1.25mW to 100mW, using 3 Revo, 2 Oplink and 2 Sparky2 boards.

Did you try all power levels from 1.25mw to 100mw (in particular 1.6 and 50)?  I only tested 1.6mw and 50mw so far and have not tested 1.25 or 100 for range.

I have a Field Strength Meter kit here that I now need to build when I get the time.  :)

I can tell you that a 50mw OpLink (with Nano) in an aircraft produces about -23dbm in GCS where a 50mw Revo in an aircraft produces about -42dbm in GCS (aircraft in "same" location, exact same aircraft antenna (moved)).

Walking down the road with aircraft test: The same aircraft gets better telemetry range at 1.6mw than it does at 50mw (GCS at 50mw for all tests).

Really I tested three complete aircraft, two with authentic OP Revos and one with authentic OP Nano/OpLink, so it isn't just one bad setup.  Always bad results with any aircraft that has a Revo at 50mw.

I have a wife "honey do" list before I can spend much more time on this...   ::)

f5soh

  • *****
  • 4363
    • LibrePilot
Quote
Did you try all power levels from 1.25mw to 100mw (in particular 1.6 and 50)?
Yes, i tested the 7 boards listed above and all the power settings.
Results are as expected except one Oplink (clone) where the power curve response i little bit different than others.

Brian

  • *
  • 119
Cliff,

It seems to me like it's either a hardware problem with both Revos, or, since it gets worse with higher power levels, some sort of ground reflection interference. Radios never work well close to the ground. The difference between the Revo and OPLink setups could be ground plane related.

You might have a larger/better ground plane when you have the two boards connected than just the Revo ground plane. It may seem silly, but you might try connecting the OPLink to the Revo, not configured to transmit, but just to act as a ground plane extension and see what that does. I've seen some weird effects like that in the past.

It would also be useful to do some more controlled tests, like plotting the RSSI in both configurations at different power levels and a few different ranges. I believe you can also get the remote RSSI from a UAVO now. I remember working on that, but I don't remember what the UAVO is off hand. If you use OPLink you have to configure it as a serial link and use OPLinkReceiver, although I think you can also get it off a channel of the PPM stream as well.

Unfortunately I'm moving soon and have packed most of my RC stuff, so I can't test ATM.

...some sort of ground reflection interference. Radios never work well close to the ground. The difference between the Revo and OPLink setups could be ground plane related.

The first case was me using [email protected] to send PPM to [email protected] (control and data) in the new fixed wing during it's first flight.  It was probably 50m altitude, so that at least was not a problem with it too close to ground.  FYI, I lost both telemetry and control, so the packet was not even getting to the aircraft.  That GCS setup sends just fine to a 1.6mw setup in the air a mile away!

I have another, similar rig, with ground 50mw too, but air is 1.6mw and get telemetry from a mile away.  This "another" rig shows the same issues when I increase air from 1.6mw to 50mw.  I have a quad with a Nano + OpLink that does as expected when increasing from 1.6mw to 50mw though!

Details:
GCS antenna was about 1.5m above ground (grass).  Intermittent loss of control (obvious when motor stops) at several times and several places.  Final full loss of control at perhaps 200m horizontally gliding perpendicular to me.  Both antennas straight up.  The aircraft was in attitude mode and gliding level.  The motor stopped. It was 10-20 seconds before it hit the trees.  I was holding full aileron (bank angle) the whole time.  No motor change.  No bank change.  No telemetry received.  I could not wave the Tx antenna because I am using a "relay box" and the ground OpLink was not actually part of the RC transmitter.

You might have a larger/better ground plane when you have the two boards connected than just the Revo ground plane.

I will remember that, but remember that it works fine at 1.6mw...

It would also be useful to do some more controlled tests, like plotting the RSSI in both configurations at different power levels ...

I intend to examine both RSSI's for received power level at some fixed range and to determine noise floor from RSSI just before loss of sync.


Musings:

Does this say that the non-coordinator is actually transmitting something even when it doesn't hear the coordinator?  I think I recall that the 72mhz RC had problems at 433mhz OpLink 50mw but not 1.6mw even with no GCS OpLink.  That is so crazy that I must recreate to believe myself.

Maybe the ground is trying to send a multipacket UAVO (or at least the PPM packet is split at the end of the buffer).  The first half gets through.  Still no valid control has been received.  The aircraft sends at high power and the aircraft AGC is then bad enough that the aircraft doesn't hear the (next) rest of the packet.

Do I remember OpLink problems with data + control from OP days?  Recommendations to only do one or the other?  This could be related.

I need to try an OP dipole with a ferrite bead which would probably have the lowest SWR of all my antennas.

Try a Sparky2 which has an LC filter on the RF.