|Feb 25, 2012, 01:19 PM|
Sid already answered that question.
Chainlink indicates Rf RSSI, and Rangelink indicates % packets received. It does not
require anywhere close to 100% Rf RSSI to receive 100% of the packets (more like about 25-30%),
which is why Rangelink continues to show 100% almost right up to the point where it loses
the signal completely.
Think of it this way. Your cell phone has an Rf signal strength indicator. 0-5 bars.
Yet you get the same voice quality usually all the way down to 1 bar and then
you might get a few seconds of broken up voice, before it either recovers
or drops the call.
What Rangelink is currently showing is basically an indication of voice quality.
It sounds good for a long time then quits. What Chainlink (and most other UHF systems)
are showing is the Rf signal strength, or reception bars.
The latter is more useful for FPV because it goes down progressively with range, and
will show when you have sub-optimal antenna orientation or external interference
and so forth. Yes it'll tend to jump around a lot more, but it's better than
a steady dummy gauge.
|Feb 25, 2012, 01:25 PM|
|Feb 25, 2012, 01:32 PM|
anything over 0 it thinks it's still getting some packets, but in my range testing I found
that response was noticeably degraded pretty much any time it drops much below 100%
and when drops it often does so very quickly. Your 0.8v was pretty close to total
loss of link, probably due to flying behind terrain.
|Feb 25, 2012, 01:44 PM|
rangelink calculates the mean of rssi in 5 second and shows it ?
real rf rssi:
rangelink calculates and show:
3.0v+1.0v+2-5v+3.2v+2.1v / 5 = 2.3v rssi
i don't know if this concept is correct
|Feb 25, 2012, 01:56 PM|
No, it's not correct, or even close.
It's about bandwidth. The actual RC control signal does not require a lot of bandwidth
to send 100% of the control packets. A strong Rf signal provides many times the
needed bandwidth. Only when the Rf signal strength drops 70-75% can it no longer
provide enough bandwidth for the control signal to pass 100% of the packets.
The problem is, things move pretty quickly in that last 25% of Rf signal strength and if
it drops below that, the % packets received drops very very fast. Since RL RSSI
indicates only % packets received, it'll go from 100% to 50% to 0 in moments.
Again, the cell phone analogy is still the most useful. Modern cell phones use a relatively
small bandwidth digital signal to pass the voice. You can pass that voice signal without
noticeable degradation all the way down to 1 bar (out of 5). Below 1 bar, the voice signal
will degrade quickly or call will be lost. Rf RSSI is like the signal strength bars..
% packet loss indicator (what the RL Rx has) is like the perceived voice quality.
It's good 95% of the time, and then real bad real quick.
|Feb 25, 2012, 06:43 PM|
ok ian, i understand, thank you, you're very helpful.
however i always flown with old chainlink, and today i tested the rangelink.
if i also not considere the rssi, the performances of rangelink are incredible compared to old chainlink.
in the places where chainlink getting some failsafe at @500mw, rangelink worked perfect @200mw... the test is made with 2 different plane and the result was always the same!!
i'm so confused, i've don't understand if sid can explain this differance and i also want to know what will include the new fw and when it will installed.
|Feb 25, 2012, 07:37 PM|
I can't speak to Chainlink (Rangelink evolved from the original Chainlink), but one thing that
attracted me to Rangelink is that the specifications say that the RL Rx has a SAW filter
installed, which should narrow it's view of the spectrum and block out more external
interference from nearby bands (Digital TV is often broadcast on a band pretty close
to this). It's possible that Chainlink Rx does not have this added filtering, and thus will
have less range in a high Rf noise environment. There may be some other reason.
To really do a proper comparison you should use the exact same antennas on the Tx
and Rx, for both systems, mounted the same way.
|Feb 25, 2012, 09:29 PM|
I was out this morning with both Skywalkers.
Each has the same gear:
4S-5000 motor only
3S 1800 electronics, camera, FY21ap
camera servo with ferrite ring. rings on all servos
the vid shows the worst effected, I aborted at 5km, I couldn't hear the engine surge, rather saw the cam servo glitch, & "felt" the rudder pull to the left. I set the FY to return to launch, & experienced no further trouble.
The second SW glitched once over the same area, I ignored it & returned to home.
Never had this happen, any ideas??
|Feb 25, 2012, 10:10 PM|
|Feb 26, 2012, 12:33 AM|
I understand that I've become the designated bad guy for pointing out the obvious,
but wouldn't you expect to find more Chainlink owners in the still active Chainlink thread?
As someone who's owned and flown a lot of UHF control systems, I can say there's just not
enough detailed information to provide a specific diagnosis. In my experience, if I get failsafes
at relatively close range with clear LoS then usually it's due to one or more of
1. Antenna problem (bad connections, bad placement, bad orientation, Tx antenna too close to the ground, etc..)
2. External interference from a source onboard the plane (lots of noisy flight cameras, noisy GoPro, other noisy HD cameras including the keychain cams, noisy voltage regulators, some video Tx frequencies matched with some UHF systems lacking certain types of filtering, certain types of digital servos... etc.. ) installed too close to the UHF Rx or Rx antennas.
3. External interference from a source outside the plane (High powered digital TV broadcast towers are my nemesis, but have been hit by other UHF control systems nearby as well)
While low powered or attenuated (terminator on the Tx antenna, or entire Tx placed in a Faraday
cage.. ala microwave oven) range tests aren't definitive, they do have some value in diagnosing
the first two categories of issues. Set a baseline range with only UHF Tx/Rx powered, and then re-test with
the various other components powered up. If you have two Rx and they're behaving differently,
test them in isolation and if one is still different, then it's an Rx problem. If they behave
differently only when when installed on their respective planes, then it's likely
a problem with something on the plane.
|Feb 26, 2012, 04:43 AM|
exactly ! my test show that the range is the same with only the rx on and in only perfect condition.
the difference on a plane is really big. i tested rangelink vs chainlink in 2 different planes and chainlink lose every time.
really big difference!
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