RF module for spectrum?

[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