(04-07-2025, 03:04 PM)flyingw Wrote: Erhard,

Please consider the possibility that you experienced some temporary lockouts.  These can happen when the line of sight between the transmitter and receiver is blocked by equipment and or other parts in the airplane.  The XPS system will hold a servo at the last position for which it saw a good control signal.  If the receiver receives a good signal again before the two-second failsafe timer expires, then no failsafe is declared and the system continues on from there.  If the receiver does not see a new signal by the time the failsafe timer expires, then it (or the X10) will declare a failsafe condition and put the servos into whatever "User" positions you configured.  Or, it will leave them in the last known position if you configured "Hold" as the failsafe output.    I determined that in my case my system never went into failsafe while flying - I felt only the short gaps in control.

These equipment and parts that can block the signal includes servos, servo wiring, metal landing gear struts, ESC and wiring, batteries, and carbon fiber parts.  I had a plane with which I experienced temporary lockouts and the problem was repeatable with two different radio systems - Futaba and XPS.  Turned out it wasn't the radio system, it was the location of the receiver antennas relative to that other stuff.

I could reproduce the problem by setting my transmitter on a chair in low power mode, and then walking the airplane away from the transmitter until the system went into failsafe.  Just before reaching that failsafe distance, I tilted the airplane into differing orientations with respect to the transmitter.  I found an orientation where failsafe came much closer than the failsafe check distance (about 100 to 150 feet).  It was just about the same orientation that the airplane was when in flight and I experienced the lockouts.

I ultimately located the receiver antennas (dual antennas on the RFU) with one element pointing aft, and the other pointing down and out through the bottom of the fuse.  The element pointing down below the fuse was "out of the way" of the large aluminum landing gear part.  After relocating the antennas out of the way of the other stuff in all orientations I haven't had the problem since.  I'll bet the XPS Nano would have also worked fine if I placed it below that big aluminum landing gear.

Paul

(04-07-2025, 11:17 AM)XPS Wrote: Let's say you are using the same transmitter that has an output power of 100mw EIRP with 2 different receivers - one has a sensitivity of  -92dBi and the other receiver has -98dBi of sensitivity.  If you get 1000 feet of range out of the receiver with -92dBi of sensitivity you will get 2000 feet of range out of the receiver with -98dBi of sensitivity.  You can also get 2000 feet of range with the receiver having -92dBi of sensitivity if you make the transmitter's output power 400mw (4x the power).  The FCC does not allow that high of power though because there is no way possible to pass spurious emissions and peak power limits.  The only way to increase range is to have very sensitive receivers.

You are using a different transmitter with the Spektrum setup. This could be something as simple as a pot that is dirty, which can cause exactly what you describe.

(04-07-2025, 05:37 PM)erhard52 Wrote:

(04-07-2025, 11:17 AM)XPS Wrote: Let's say you are using the same transmitter that has an output power of 100mw EIRP with 2 different receivers - one has a sensitivity of  -92dBi and the other receiver has -98dBi of sensitivity.  If you get 1000 feet of range out of the receiver with -92dBi of sensitivity you will get 2000 feet of range out of the receiver with -98dBi of sensitivity.  You can also get 2000 feet of range with the receiver having -92dBi of sensitivity if you make the transmitter's output power 400mw (4x the power).  The FCC does not allow that high of power though because there is no way possible to pass spurious emissions and peak power limits.  The only way to increase range is to have very sensitive receivers.

You are using a different transmitter with the Spektrum setup. This could be something as simple as a pot that is dirty, which can cause exactly what you describe.

by "pot" you mean the pot in the servo?. if that were the case it should be RC system independent right? which it is not.
i understand your above description. RF power ideally drops of with 1/distance^2

(04-09-2025, 09:47 AM)XPS Wrote: The output power of the XPS RF modules is 100mW EIRP.

The over-air system that the XtremeLink system uses is unique from all others,  It uses 5MHz of bandwidth for its spread spectrum transmissions.  Spektrum uses 1MHz.  Futaba uses 100KHz.  JR DMSS uses the exact same over-air system we do (it was adopted by JR), but the packet data is different.

You can program the settings of any of the XtremeLink products using the XDP.

Your assumption about the power difference is incorrect.  -30dbM to -22dBM is 8dBm, every 6dBm is double the power output.  Our system is 100mW EIRP, and Spektrum is 200mW EIRP.  You have to be measuring the power output at the antenna connector to determine the true output power.  Antenna angle itself can reduce the range to nearly 0%.  Point the tip of the antenna at your spectrum analyzer and you will understand what I mean.  It's difficult to try to determine much from a simple analyzer just holding a transmitter.

As stated previously, receiver sensitivity is what determines the range.  A built-in (PCB) antenna is probably in the -89dBi to -91dBi sensitivity range, maybe less.  Our Nano receiver is -102dBi and the RFU is -107dBi.

(04-10-2025, 01:22 AM)XPS Wrote: You are not understanding what you are measuring.  If you place your transmitter 10 feet away from your analyzer you are going to see a much different result.  That device is measuring the signal strength as it sees it.  The only way to measure output power is by a direct connection.

Anytime you see a negative (-) value that means receiving signal strength.

You can find various calculators online that will show you some simple things, like for output power 100mw = 20.0dBm, and 200mw = 23.01dBm.  Again, this is output power.  Remember it takes basically 4x the output power (400mw vs. 100mw) to double the effective range.  Every 6dB doubles the range - either via transmitter output power (26dBm = 400mw) or by having a 6dB increase in receiver sensitivity.

(04-11-2025, 09:50 AM)XPS Wrote: Again, you do not understand how power measurements work.  Every 6dB doubles the effective range.  What you see is NOT a factor of 6.3.  8dB is a factor of 8/6dB, which is a factor of 1.33333.  However, your measurement is subjective to the antenna angle, distance, and the environment.  This is why a direct connection is used during FCC testing.

100mW = 20dBm
200mW = 23dBm
400mW = 26dBm

What you are missing here is the receiver sensitivity.  Spektrum receivers typically report a sensitivity of -92dBi.  We know from testing built-in antennas in the past (we had a 3 channel receiver we sold that used a similar antenna) that the sensitivity is typically a bit lower.  So we expect the AR410 sensitivity to be -89dBi to maybe -91dBi.  The Nano receiver has a sensitivity of  -102dBi.  That is a difference of 10 to 12dBi.  So, somewhere between 3.333 to 4 times the range when using the exact same transmitter output power.