Balance P and D Gains with Step Response
Read a step-response graph and use it to find a practical balance between P and D gains for your FPV quad.
Test a Jumper T15 radio link, interpret signal-quality results, and spot setup issues before flying.
What this tutorial covers
This guide uses FPVSIM Blackbox Analyzer to compare RC-command noise from a Jumper T15 and a modified FrSky X9 Lite. The same method can help you inspect a radio or gimbal after damage, wear, contamination, or an unexplained change in control feel.
A spectrum graph is a comparison tool, not a pass-or-fail certificate. Match the aircraft, receiver link, packet rate, logging setup, and flight maneuver before attributing a difference to the radio. Inspect and repair a suspected hardware fault instead of hiding it with filtering.
Prepare comparable logs
- Back up the radio and flight-controller configuration before testing.
- Bind both radios to the same quad and use the same ExpressLRS packet-rate settings.
- The video uses ExpressLRS at 1000 Hz and Blackbox sampling at 2 kHz so the log can represent that command stream.
- Choose a safe test area, remove propellers for every bench check, and label each log as soon as it is recorded.
Compare RC command quality
Match both setups
Confirm that the quad, receiver, packet rate, flight-controller configuration, and Blackbox logging rate remain unchanged. Change only the transmitter under test.
Fly repeatable inputs
Record a short flight with smooth stick movements and several similar turns on each radio. Avoid comparing a calm hover from one log with an aggressive flight from the other.
Open RC commands in FPVSIM
Load the first log in Blackbox Analyzer, open Input and response, choose RC commands, and select the Spectrum graph.
Inspect every axis
Compare roll, pitch, yaw, and throttle. Look for a raised high-frequency noise floor, narrow spikes, or one axis that is visibly hairier than the others.
Load the comparison log
Open the second radio's log with the same analyzer view and graph scale. In the demonstration, the Jumper T15 trace is cleaner than the modified X9 Lite, especially on the older radio's pitch axis.
Investigate the physical cause
Recalibrate the radio and inspect the gimbal, wiring, connectors, sensor area, and firmware. Dust, wear, impact damage, or a poor connection can all deserve attention before software smoothing.
Retest after any change
Record another matched flight and compare it with the original evidence. Keep the fix only if the high-frequency behavior and real control feel both improve.
Interpret the spectrum carefully
- Most deliberate human stick motion appears at relatively low frequencies.
- In this comparison, the creator treats substantial content above roughly 50 Hz as likely noise and content above 100 Hz as unwanted; those are diagnostic observations, not universal radio specifications.
- A narrow feature near the 1000 Hz link rate can come from timing or sampling behavior and does not by itself prove a bad gimbal.
- Noisier command data may require more feedforward smoothing, which can add latency. Correcting the source is preferable when a hardware problem exists.
Edited transcript
This transcript has been cleaned for readability. Timestamps are approximate, and the conclusions describe this matched comparison rather than every unit of either radio model.
00:00–01:00
The comparison uses a DIY-modified X9 Lite with AG01 gimbals and a Jumper T15. The same quad is bound to both radios so Blackbox logs can be compared under similar conditions.
01:01–02:05
Both links run ExpressLRS at 1000 Hz. Blackbox is configured at 2 kHz because a sampling rate above the command rate is needed to examine the 1 kHz signal without losing the relevant frequency content.
02:06–03:08
Record separate flights for the two radios. In FPVSIM Blackbox Analyzer, open Input and response, select RC commands, and switch to the Spectrum graph.
03:09–04:37
Human stick movement is concentrated at low frequencies. The creator uses activity above about 50 Hz as an indication of likely noise in this test and considers activity above 100 Hz unwanted rather than intentional pilot input.
04:38–05:59
The X9 Lite log has a visibly higher noise floor and many fine spikes. Its pitch command is particularly noisy, suggesting a problem associated with that gimbal or axis. A line close to 1000 Hz may represent link or sampling jitter.
06:00–07:18
The Jumper T15 log is cleaner across the same view. Because the quad and link configuration were held constant, the comparison points toward a transmitter-side difference, although it does not identify the exact damaged or contaminated part.
07:19–08:23
A noisy RC command can require more feedforward smoothing. Smoothing reduces how much command noise reaches the control loop, but extra smoothing also adds response delay, so it is better to correct a physical signal problem when possible.
08:24–09:10
The settings shown are personal examples rather than values to copy. Use matched logs to understand your own radio, inspect any suspicious gimbal, and confirm the result after repair or recalibration.
Frequently asked questions
Does this video prove every Jumper T15 is cleaner than every X9 Lite?
No. It compares two specific radios, including a modified older unit that may have a pitch-gimbal problem. Use the method to evaluate your own hardware.
Why log at 2 kHz for a 1000 Hz ExpressLRS link?
The tutorial uses the higher sampling rate so the log can represent the command stream for spectrum analysis. Lower logging rates can omit or alias high-frequency content.
Is everything above 50 Hz definitely gimbal noise?
No. That threshold is the creator's practical interpretation for these logs. Link timing, sampling, filtering, and other electronics can also create high-frequency features.
Can feedforward smoothing fix a noisy radio?
It can reduce the effect of command noise, but it may add latency and can mask a hardware problem. Inspect, recalibrate, and repair the source first when possible.
Why compare all four channels?
A single noisy axis can stand out against the others and point toward one gimbal sensor, connection, or calibration issue.
