RF module for spectrum?

[erhard52]

Erhard,

Your 60% link quality at link failure is uncomfortably close to your 70% flight result.

I've read about folks tuning their 4in1 units to improve the performance.  The procedure is done right from the transmitter.  I do not know how as I have never done it.  Maybe that would increase your safety margin for the sailplane.

Paul

thanks Paul
the tuning is easily done on the radiomaster system, and i did it - yes this is for the 4-in-1 module.
you basically detune it on both sides - lower and higher frequency side and then use the middle value.
you detune it until link breaks on either side.

my the range test still refers to the XPS  module in my multiplex but i get similar range data with the XPS F1 module. 
how can it only be 2m when drew says it should be 30-50ft without TX antenna?

drew always makes it sound like the range is more dependent on the receiver sensitivity than the output power. in the end the range should still depend with 1 over square on the output power.
my receiver antenna ends are now out on the wing and orthogonal to each other.
drew says somewhere that in range test the output power is 0.15mW so in regular mode we have like 50mW? that would be 17x more range. that makes 20m to about 300m. to be honest that sounds about what i see with the glider. 
the main problem is that my actual range test distance is at least 2 x short i think than what it should be.
maybe i can repeat the range test with the radiomaster system and removed antenna.


you are right the 70% or sometimes only high 60ies is not making me feel good either. only argument i have it is a glider and does not need super fast response in case of soaring. 
what nags me as an engineer is that i do not understand what is causing this issue. my output power is at level 5 per XPS instructions.

[flyingw]

Erhard,

Please do not run the RadioMaster transmitter or the 4in1 module with the antenna removed - it could burn out the RF output electronics.  The XPS transmitter modules were the only RC system I ever heard of that could run safely with the antenna removed, and still I never do it (I burnt out some other brand once by turning a transmitter on and forgetting that no antenna was screwed on).

Am I understanding this correctly:  You are getting only two meters of range with both the Multiplex XPS transmitter module and the XPS-F1 (Futaba) transmitter modules?  And that is without the antenna.

Try it with the antenna, but in range test (low power) mode.  Do you get the 125 feet before the servo movements become erratic?

By FCC regulations, all transmitters that are sold in the USA must not exceed 100mw transmit power - and that includes any focusing performed by the antenna.  The actual output of the transmitter module is about 65mw.  The antennas are typically 2.15dB and that brings the total power that the FCC cares about up to about 100mw.  This is at XPS power level 5 (the default) in the transmitter module.

If we have 100mw to work with, then the best way to get more range is a better receiver.  The XPS receivers are outstanding in this respect with the Nano having a sensitivity of something like -102dB and the RFU with -109dB.  Those extra 7dB with the RFU doubles the range over the Nano.  I reckon that the 4in1 and the Spektrum receiver doesn't have as good a performance as that.

My typical range check with an XPS transmitter module and Nano or RFU receiver with the transmitter antenna in place and transmitting in low power mode is about 130 feet.  Give that the low power mode is about 41 times less than full USA power of 65mw, I calculate the theoretical range to be about 41 x 130 = 5,330 feet or just over a mile.

I once flew a plane with an autopilot on a farm out to 2,300 feet away.  The signal strength reported by the Nano receiver was about -85dB.  I was using the XPS Telemetry Station to get these measurements.

Yeah, so I think your range test result and 300 meter result is too low.  Make sure you have failsafe set to bring the sailplane down so it doesn't fly away.

Paul

[erhard52]

Erhard,

Please do not run the RadioMaster transmitter or the 4in1 module with the antenna removed - it could burn out the RF output electronics.  The XPS transmitter modules were the only RC system I ever heard of that could run safely with the antenna removed, and still I never do it (I burnt out some other brand once by turning a transmitter on and forgetting that no antenna was screwed on).

Am I understanding this correctly:  You are getting only two meters of range with both the Multiplex XPS transmitter module and the XPS-F1 (Futaba) transmitter modules?  And that is without the antenna.

Try it with the antenna, but in range test (low power) mode.  Do you get the 125 feet before the servo movements become erratic?

By FCC regulations, all transmitters that are sold in the USA must not exceed 100mw transmit power - and that includes any focusing performed by the antenna.  The actual output of the transmitter module is about 65mw.  The antennas are typically 2.15dB and that brings the total power that the FCC cares about up to about 100mw.  This is at XPS power level 5 (the default) in the transmitter module.

If we have 100mw to work with, then the best way to get more range is a better receiver.  The XPS receivers are outstanding in this respect with the Nano having a sensitivity of something like -102dB and the RFU with -109dB.  Those extra 7dB with the RFU doubles the range over the Nano.  I reckon that the 4in1 and the Spektrum receiver doesn't have as good a performance as that.

My typical range check with an XPS transmitter module and Nano or RFU receiver with the transmitter antenna in place and transmitting in low power mode is about 130 feet.  Give that the low power mode is about 41 times less than full USA power of 65mw, I calculate the theoretical range to be about 41 x 130 = 5,330 feet or just over a mile.

I once flew a plane with an autopilot on a farm out to 2,300 feet away.  The signal strength reported by the Nano receiver was about -85dB.  I was using the XPS Telemetry Station to get these measurements.

Yeah, so I think your range test result and 300 meter result is too low.  Make sure you have failsafe set to bring the sailplane down so it doesn't fly away.

Paul

Q: Am I understanding this correctly:  You are getting only two meters of range with both the Multiplex XPS transmitter module and the XPS-F1 (Futaba) transmitter modules?  And that is without the antenna.
A: yes you understand that correctly AND i am in power mode 5. confirmed with 5 green flashes.
and that is very strange isn't it? i also checked with 2 different RFUs and the same result.

WITH TX antenna but range check mode -low power -i get 20m (60ft) at most. that means antenna not directly pointing at receiver and my body not on between. just very poor.

today i flew at max 300m away -line of sight and LQI dropped to high 70ies. i think it should be in the mid 90iies if everything works right.
i am running out of ideas on what to test.

so 2 different XPS modules give the same result and 2 different RFUs give the same result. 
--> conclusion: all components work as advertised but something is not right

thanks for the tip to NOT to remove the antenna from the radiomaster.

i had bought one of these tiny spectrum analyzers while back to measure the transmitter but it is difficult to draw any conclusion and due to the hopping it is even more difficult to get a power measurement.

no need to look at it but if you are curious here some not really conclusive results results
RC transmitter output power measurement with spectrum tinySA.docx

ok more testing:
i still had the XPS 8 channel receiver in my synergy s914 glider.
i tested it with the XPS-F1 module. similar to the the other tests.
without antenna and low power mode range was 2-3m
with antenna and low power: at about 20m missing frames and at 30m (100ft) all gone

i also bound that XPS-F1 to the nano receiver and got about the same results

so under in no circumstances did i get your range, or at least i am about 30 lower. so could this just be the cabling in the model?
i remember reading way back in a book that the receiver elevation above ground is quite significant too. XPS asks for 6" above ground.

ok went back and used the laser range meter just to make sure my estimates were not too far off.
maybe that is just it.
i keep monitoring my LQI when i am flying and i know below 70% is not ideal

[XPS]

The range test with any v3.x modules is done with the antenna always ON. Only the very early 1.x/2.x modules (up to about 2007) did the range test with the antenna OFF. Look at the LED on the transmitter module when you turn on the transmitter. Once connected to the receiver the LED will flicker it is is a v3.x module. Otherwise the LED will be solid green.

[erhard52]

The range test with any v3.x modules is done with the antenna always ON.  Only the very early 1.x/2.x modules up to about 2007) did the range test with the antenna OFF.  Look at the LED on the transmitter module when you turn on the transmitter.  Once connected to the receiver the LED will flicker it is is a v3.x module.  Otherwise the LED will be solid green.

Paul
ok both of my modules flicker green when connected - so no antenna removal. thanks a lot for this information. where did you find that one?
so the next question then could: " are my modules no damaged because i too the antenna off?
how to know and potentially fix it. 
i wish RF power measurement would not be so difficult. 
there should be a test mode that turns the hopping off for that purpose then i would have a better chance to measure RF power.
the tx16s also has a built in spectrum analyzer but there i also do not see a useable difference when i power any other transmitter on or off

erhard

[flyingw]

Erhard,

I do not have any real lab equipment to measure the output of the transmitters.  I tried using an Immersion RC Power Meter, but since the transmitter signal is hopping and has a low average power, I could only get vague results.

However, I did get repeatable results using the XPS XDP device in conjunction with the XPS RSSI application.

I have repeated this test with my XPS JR and XPS Futaba transmitter modules and the results were pretty much the same.  Using the XDP device:

Bring up the Tx RSSI tester application and place the working transmitter 3 feet away.  I just did this test with my Taranis and XPS-J1 transmitter module.  At 3 feet I saw signal strength numbers in the area of -40dBm.

   

Then I moved the transmitter to a spot about 20 feet away and the new RSSI numbers were about -61dBm.

   

Then, still about twenty feet away, I placed the transmitter in my refrigerator (a big metal box) and the RSSI went down to -77dBm.

Since both of my transmitter modules produced similar results, I decided that they were both working properly.

The RSSI numbers can vary quite a bit based on the relative location of the transmitter and the XDP device.  I wasn't so concerned about the absolute numbers.  The test can, however, give a good comparative results to see if one transmitter module is performing differently from another.

Paul

p.s.  With the RSSI application running, you can press the low power button (range check mode) on the back of the transmitter module and see the overall signal strength go down.

[erhard52]

Erhard,

I do not have any real lab equipment to measure the output of the transmitters.  I tried using an Immersion RC Power Meter, but since the transmitter signal is hopping and has a low average power, I could only get vague results.

However, I did get repeatable results using the XPS XDP device in conjunction with the XPS RSSI application.

I have repeated this test with my XPS JR and XPS Futaba transmitter modules and the results were pretty much the same.  Using the XDP device:

Bring up the Tx RSSI tester application and place the working transmitter 3 feet away.  I just did this test with my Taranis and XPS-J1 transmitter module.  At 3 feet I saw signal strength numbers in the area of -40dBm.



Then I moved the transmitter to a spot about 20 feet away and the new RSSI numbers were about -61dBm.



Then, still about twenty feet away, I placed the transmitter in my refrigerator (a big metal box) and the RSSI went down to -77dBm.

Since both of my transmitter modules produced similar results, I decided that they were both working properly.

The RSSI numbers can vary quite a bit based on the relative location of the transmitter and the XDP device.  I wasn't so concerned about the absolute numbers.  The test can, however, give a good comparative results to see if one transmitter module is performing differently from another.

Paul

p.s.  With the RSSI application running, you can press the low power button (range check mode) on the back of the transmitter module and see the overall signal strength go down.

thanks Paul
yes i remember you shared that data with me earlier and i also repeated it need to look up my numbers again - or better remeasure.

adding:
when i flew today repositioned the receiver antenna - the ends are already on top of the wing, one parallel to the fuselage and one perpendicular - now i basically turned this setup by 45 degrees. so now both antenna parts are about same distance from the conductive (carbon) fuselage. i also pointed the transmitter antenna 45 degrees down to the ground instead usually i have it point basically to my chest. this all did not make a difference -

one thing is not ideal with the LQI. if the number is not changing it is not clear if there was no update or the number was the same because for at least 30 sec it was fixed on 80%.
anyways so far i have not noticed any dropouts

[erhard52]

another scary observation.
while setting up another plane with x10v1 and RFU everything seemed ok and i turned off the transmitter and voila one aileron servo went to the full deflection. turning the transmitter on brought it back , turned off again and all servos stayed where they were.
my failsafe is 'keep last position'

a few minutes later the same happened but a different servo.

now in a possible defense of the system i need to mention this: the receiver and servo voltage was very low - clearly below 5V and most likely around 3.8-4V
i know that is not good and i also realized later that the RFU LED was RED which i think indicates a low voltage situation

[flyingw]

Erhard,

The XPS manual for the RFU says that its led will turn orange if the power supply falls below 4.5v.

Paul

[erhard52]

Erhard,

The XPS manual for the RFU says that its led will turn orange if the power supply falls below 4.5v.

Paul

yes i know and it was red but i did not pay attention initially - 
funny observation: while accidently brushing on a control surface the servo moved and it lit up the x10 LED in red.
the system was not power up.
no real surprise because the servo motor acts as generator but i never thought about this. so the entire RC electronics better be well protected against reverse polarity!

i had a long chat yesterday with AI regarding receiver sensitivities and when not counting long range receives are dual band then the XPS always comes out at the top. the benefit is due to its heterodyne input stage vs simple SDR designs. 
even the multiplex M-Link is only in the -90dBm vs RFU more like -95-100.
however that RFU benefit can go away in RF noisy environments which i think makes sense.