Frequency Tuning
Certain protocols require tuning for optimal performance. In some cases tuning is required in order for the protocol to bind. Frequency Tuning is specific to each MULTI-Module, and is due to very small variations in the RF components.
Frequency Tuning typically only needs to be performed once per protocol, as there is usually only a small variance between the values found for multiple receivers of the same type. Once known, the same value can usually be used for all receivers which use the protocol.
Protocols which require frequency tuning are:
FrSkyD (e.g. FrSky D4R and D8R, DIY RX-F801 and RX-F802 receivers)
FrSkyV (e.g. FrSky V8R4, V8R7 and V8FR receivers)
FrSkyX (e.g. FrSky X4R, X6R, X8R, XM+ and XSR receivers)
S-FHSS (e.g. Futaba S-FHSS receivers)
Corona (e.g. Corona V1 FSS, Corona V2 DSSS CR8D/CR6D/CR4D and FlyDream IS-4R/IS-4R0 receivers)
Hitec (e.g. Optima, Minima, Micro and RED receivers)
HoTT (e.g. Graupner receivers)
Any protocol which can use the CC2500 RF module to emulate XN297. This will be noted on the protocol details page, e.g E010, V911S, and others.
The general rules is that if the RF Freq. fine tune option appears in the protocol menu, frequency tuning is required and should be performed.
RF Freq. fine tune option
Frequency Tuning is always recommended, but especially when:
It is difficult to bind to the receiver, or the connection is weak or intermittent
Control range is very short
Telemetry data is not received or (for telemetry-enabled receivers only)
Completing the Frequency Tuning Procedure ensures that the radio and receiver will have the strongest possible connection.
If you change the frequency tuning value it is best to re-bind the receiver(s).

# Frequency Tuning Procedure

The procedure can be performed in serial or PPM mode. It is easier in serial mode because the effect can be observed in real-time.
For best results, the fine-tuning procedure should be carried out with a genuine FrSky, Futaba, Corona, Hitec, or HoTT receiver.

## Preparation

If the receiver does not bind, and the RF Freq. fine tune option is available for the protocol, change the RF Freq. fine tune value to either -40 or 40 and try to bind again. If binding is still unsuccessful, continue to try higher and lower values in steps of plus or minus 40 until the bind succeeds.
RF Freq. fine tune
Make sure you try the whole range of RF Freq. fine tune values, -127 to +127.
See the Binding documentation page for more details instructions on completing the bind process.
Once the receiver is bound you can proceed with Fine Tuning.

## Serial Mode Fine Tuning

If you have telemetry configured and a voice-capable radio, you can enable a voice alarm for telemetry loss so that you receive an immediate alert when the receiver connection is lost.
With the radio is bound to the receiver:
1.
Return to the RF Freq. fine tune option
2.
Lower the value until the radio loses the connection with the receiver. Record the value (TUNE_MIN).
3.
Raise the value so that the connection is restored, then continue to raise it until the radio loses the connection with the receiver again. Record the value (TUNE_MAX).
4.
Calculate the median between the two values (TUNE_MIN + TUNE_MAX) / 2 = TUNE_MEDIAN
5.
Set RF Freq. fine tune to the median value
Example
Connection is lost at -73 and +35; the median is -19:
$(-73 + 35) \div 2 = -19$
Once the Fine Tuning value is known, it can be used for all models which use the same protocol.
If you compile your own firmware build you can set the Fine Tuning value in the firmware, removing the need to configure it on each model.

## PPM Mode Fine Tuning

Fine Tuning in PPM Mode requires configuring multiple switch positions with the same protocol, but with different fine tuning values, then compiling and uploading the firmware and testing each value. The compile-upload-test process will need to be repeated several times to get an accurate fine tuning value.
You will need to be familiar with configuring and compiling the MULTI-Module source code. See the Compiling the Firmware page for more information.

Users who compile their own MULTI-Module firmware can specify pre-set frequency fine tuning values in the firmware, so that they automatically apply to a given protocol.
When configuring the firmware source, locate and edit this section in _Config.h:
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/*******************************/
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/*** CC2500 FREQUENCY TUNING ***/
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/*******************************/
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//For optimal performance the CC2500 RF module used by the FrSkyD, FrSkyV, FrSkyX, SFHSS, CORONA and Hitec protocols needs to be tuned for each protocol.
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//Initial tuning should be done via the radio menu with a genuine FrSky/Futaba/CORONA/Hitec receiver.
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//Once a good tuning value is found it can be set here and will override the radio's 'option' setting for all existing and new models which use that protocol.
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//Valid range is -127 to +127
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//Uncomment the lines below (remove the "//") and set an appropriate value (replace the "0") to enable.
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//#define FORCE_FRSKYD_TUNING 0
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//#define FORCE_FRSKYV_TUNING 0
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//#define FORCE_FRSKYX_TUNING 0
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//#define FORCE_SFHSS_TUNING 0
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//#define FORCE_CORONA_TUNING 0
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//#define FORCE_HITEC_TUNING 0
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//#define FORCE_HOTT_TUNING 0
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If a fine tuning value is set in the firmware, the RF Freq. tuning value from the radio is ignored.