Lemon Rx LM0086 Telemetry Stabilizer Receiver Instruction Manual

Telemetry with the Lemon Rx 7- and 10-Channel Receivers
2022-10-24
Applies to the LM0086 Seven-Channel Stabilized Receiver, LM0087 Ten-Channel
Stabilized Receiver, and LM0082 Ten-Channel Receiver (non-stabilized)

Introduction to the Receivers

The purpose of this manual is to focus on the telemetry capabilities of Lemon Rx 7- and 10-channel receivers and to provide necessary information for users on their setup, operation, and calibration. For information on other aspects of the receivers, please see the Essential Instructions, available separately [7ch, 10ch] The primary focus in this document is on use with Spektrum® transmitters, but these receivers work well with, and can deliver telemetry to, a number of DSMX compatible radios and RF modules from other manufacturers (see page 4).
The Lemon-Rx 7-Channel LM0086 Receiver and 10-Channel Telemetry Stabilized Receiver LM0087 combine in a single package the functions of a high performance DSMX/DSM2™ compatible radio control receiver, a proven rate stabilizer and a full-range telemetry unit. The 10-Channel LM0082 receiver is identical to the LM0087 from a telemetry standpoint but omits the stabilizer. In this document they are all treated as equivalent.
These receivers send back real time data to the transmitter on receiver voltage, temperature, and RSSI (signal strength). An optional V/I external sensor provides voltage (V), current (I) and capacity-used (mAh) readings for the flight pack. Or a voltage sensing wire can provide just flight pack voltage. In addition, altitude, and vertical speed (vario) data are provided by a built-in barometric sensor.
The various parameters of the telemetry data are displayed on the transmitter screen and can trigger audio tones or haptic alarms. Data values and alarms can also be spoken by voice-enabled transmitters. This is a very desirable feature that allows the pilot to take full advantage of telemetry without looking away from the aircraft while flying.
Both the radio control receiver and the telemetry transmission functions of these receivers give exceptionally good range, operating to the normal limits of unaided visual flight and beyond. This is achieved by using efficient circuit design, as well as dual antennas and antenna-switching to ensure maximum signal reliability in both directions. Note that full control is retained even after the telemetry signal is eventually lost.
The receivers will operate reliably between 4.0 and 8.5V. They can use a variety of power sources, including 2s LiFe and LiPo batteries, as well as the usual 5V or 6V power from an electronic speed control (ESC).

Lemon Telemetry

Built in sensors
Within the receivers, built-in sensors provide receiver voltage, internal temperature, and RSSI (signal strength).
In addition, a precision barometric sensor reports altitude and vertical speed (vario).
The unit sends a unique-to-Lemon RSSI (Received Signal Strength Indicator) value, which starts at 100 when the receiver is right next to the transmitter and declines as the signal drops off with distance. The RSSI value is displayed as parameter “A” on the Spektrum Flight Log screen of the transmitter. 1 Fades, holds, etc. are not recorded, but the B, L, and R fields are used to briefly display the firmware version at power on.
LiPo pack voltage and current
To provide battery-related data for electric models, there are two options. The receiver comes either with a simple total flight pack voltage sensor wire (probe), or with a combined voltage/current (V/I) sensor that measures the real-time current and allows the amount discharged from the pack in mAh to be read.
The voltage sensor wire input can tolerate up to 50V input voltage. The 60 Amp V/I sensor is rated for up to 22V (5S LiPo pack) input, while the 130 Amp V/I sensor has a maximum of 26V (6S HV pack). Variants of the V/I sensor are available with T-Plug, XT60, XT90 and EC5 connectors. Lemon do not have a sensor for individual cell voltage telemetry.
The receiver is calibrated for use with whichever external sensor is provided with it. If a different sensor is used, the receiver must be recalibrated to give accurate results. Thus, if a V/I sensor is added after purchase, or if a voltage wire is substituted for a V/I sensor, the receiver must be recalibrated by the user. For details, see Annex A, “Voltage and Current Calibration”. Voltage calibration is fairly simple, but for users intending to use a V/I sensor it is recommended to purchase the sensor with the receiver supplied in the already calibrated state.
WARNING
The receiver has identical connectors for a satellite receiver and the electrical sensor. The satellite connector is designed for 3.3V and, although somewhat protected, should not be exposed to higher voltages.
The V/I sensor has a current-limiting resistor that will protect against receiver damage if it is accidentally plugged into the satellite port. However, voltage wire protection is good only up to 35V, and this for just a few seconds. So, take care to avoid plugging the voltage wire into the satellite port.
¹ The Lemon RSSI values are not directly comparable to Spektrum or FrSky RSSI values.
Note also that there can only be a single source of telemetry for a given model. Thus, if a second receiver is used it must be of a non-telemetry type, as another data stream would interfere with that of the primary receiver.
Likewise, separate telemetry units cannot be installed with a telemetry receiver.

Connections

The photos (below) show how the Voltage sensor wire and V/I sensor are connected.

Compatible Transmitters

Spektrum Transmitters
Telemetry from the receiver can be both displayed on-screen and spoken by most recent Spektrum telemetryenabled transmitters. More specifically:

• DX6G2/3, DX7G2, DX8G2, DX9 (all versions), DX10t, DX18 (all versions except the first), and DX18t are all fully capable. Likewise, the newer NX and iX transmitters are fully telemetry-enabled with both visual displays and voice.
• The DX6e and DX8e, and the first generation DX8, DX7s and DX18, can display telemetry data on-screen and have some limited beep alerts (and, in some cases, vibration). But they lack voice capability and therefore cannot speak values or alarms.

A summary of the telemetry capability of Spektrum transmitters can be seen in this table.
Of particular importance for glider flyers will be the barometric capability of the Lemon receivers. ² When it comes to support for Altitude and Vario telemetry, there are basically four categories of Spektrum transmitter:

1. Older (up to about 2011) transmitters, including the original DX6, DX6i and DX7, as well as the JR X9303/9503, do not support any kind of telemetry.

2. The Generation 1 radios, DX8G1, DX7s and early DX18, can display altitude but not vario, and lack voice capability.
   ² It’s important to understand the difference between “vario”, which is a variable series of tones indicating rate of change of height (i.e., vertical speed up or down), and “altitude”, which is a simple height-above-ground value that can be displayed or spoken. Both use data from the same barometric sensor.

3. All the Generation 2 and above radios, from DX6 and DX6e to DX20, plus NX and iX radios, audibly support vario. They produce varying tones when the model is rising or descending. They can also display the vertical speed and height on screen.

4. All speech-enabled transmitters (see above) can announce the height as well as display it, and also have better quality vario tones.

So, for example, the low cost DX6e can display height and has adequate audible vario tones but cannot announce the height, as it is not speech-enabled.
Always make sure the transmitter is updated to the latest available AirWare.
Non-Spektrum Transmitters
The Lemon RX Telemetry receivers also operate successfully with a number of non-Spektrum transmitters equipped to be compatible with DSMX protocol; in many cases this includes support for telemetry. Some such radios, including the FrSky Taranis, Turnigy 9XR Pro and Turnigy 9x with upgrade mother board, use a JR format module, such as the Multiprotocol 4in1, Jumper or iRangeX. Other compatible transmitters include Jumper and RadioMaster products that have internal Multiprotocol RF modules.
Recent versions of OpenTX, EdgeTX and ErSkyTX firmware all support telemetry.
Lemon’s own DSMP Transmitter module (JR format) can, with certain transmitters and firmware, provide telemetry from the receivers discussed here.
For details on using a non-Spektrum transmitter with these receivers, see “Additional Information” [Not yet available].

Setting Up Telemetry on a Spektrum Transmitter

Telemetry screens generated by Lemon receivers look very much the same in most Spektrum transmitters. The  illustrations here are from a DX8e transmitter, the least capable of Spektrum’s 8 channel transmitters (and effectively the lowest desirable option for use with the receivers discussed here). Other transmitters, such as the newer NX series, may have more sophisticated display features, including color screens, but they provide essentially the same information in the same format. It’s important to review the Telemetry section of your transmitter manual, which provides key information regarding the procedure and options available for setup.
Step 1: Bind
Bind the receiver to the transmitter and allow it to Auto-Configure the sensors.
For the Telemetry heading to show up in the transmitter menu, the receiver must be bound to the appropriate model in the transmitter and powered up with all sensors connected.

When Bind is complete the transmitter will display the Main screen with the Telemetry received symbol in the top left corner. Depending on the transmitter software version, Auto-Configure may assign all sensors correctly during bind but it is recommended that it be repeated in Step 2 below.

Step 2: Select data display
You can now go to Function List, choose Telemetry and select Auto-configure. Once Auto-configure is complete, check each of the numbered items to determine what data is recognized and make changes if necessary.

Selecting Fields
The following parameters will normally be displayed automatically, depending on the availability of sensors: ³

• Receiver voltage. (Rx V) Automatic, no external sensor or lead required. Note that this is not the flight pack voltage; if receiver power is supplied by an ESC or BEC, this value will normally not vary.
• RSSI – signal strength. Automatic. This is not available on the Telemetry setup screen but is displayed on “Flight Log”, the first telemetry screen on the transmitter, as parameter “A”. 4 See Annex C.
• Temperature. Automatic transmission of the internal temperature of the receiver.
• Battery voltage (Volts). This is the flight pack voltage. If a V/I sensor is not used, this requires a connection to the battery positive using the voltage sensing wire provided. See Annex B for connection details.
• Battery current (Amps). This is the flight pack current. It requires that a V/I sensor be inserted into the main power lead. The V/I sensor replaces the voltage sensing wire and provides both current and voltage information, as well as the battery capacity used.
• Flight Pack mAh (mAh). This is the flight pack capacity used since power-up. Requires V/I sensor.
• Altitude. Automatic, no external sensor or lead required. Note that two slightly different Altitude values may be displayed, one in the Telemetry screen, the other in the Vario screen.
• Vario (vertical speed). Automatic, no external sensor or lead required. Not available on a DX8 Gen1 or DX7s transmitter.
• RPM. This value is not transmitted by these Lemon receivers and will display as blank.

Note that third party PowerBox fields are available but are not normally required by modern Spektrum transmitters. They can, however, be used by the first generation DX8 and DX18 (which do not have a Battery Capacity field).
³ There will be differences in the display of telemetry for different generations of Spektrum transmitters, as explained earlier. Note also that the Display item under Telemetry, Settings is normally set to Roller. If set to Main, no telemetry will be displayed, though audio reports and warnings will still be available.
4 Not to be confused with Spektrum’s Signal % parameter, which is also a measure of RSSI but not directly comparable.

Step 3: Understand the Screens

The first item in the Telemetry menu is Auto-Config which is normally applied automatically in the Bind process. In most cases, this will recognize and configure the available sensors, but individual items can be reconfigured separately as required.
The Telemetry page provides basic setup for on-screen telemetry  display. It does not, however, automatically enable the voice and tone signals that are essential to using telemetry effectively. To set these, it is necessary to go to the relevant items on the Telemetry page and select how they will be reported.

Use the roller to move between the numbered fields, click to select, then click again to open. You can then choose what is to be made available. Under most items, the menu allows that particular parameter to be displayed or inhibited, sets minimum and maximum values for purposes of triggering a tone or voice alarm, and determines whether status and warning reports are issued at intervals of between 5 and 60 seconds.
For example, the Altitude screen allows you to Act(ivate) the display and set Minimum and Maximum alarm values. The example has maximum set at 122m (400ft) but the tone alarm on the radio is turned off Inh(ibited).

The Vario item presents a different set of options, in keeping with the audible and graphical nature of the readout. The delay in reporting can be selected from ¼ second to 3 seconds, the onscreen graph can be set to a width of 5 to 60 seconds, and the minimum lift or sink speed to be indicated by audible beeps can be adjusted from 0.1 to 9.9 m/Sec (0.3 to 32.4 Ft/Sec). In addition, a switch can be selected to turn the Vario tones on or off.

On the Telemetry page is also a Settings item, which leads to a choice of how the telemetry display is selected and whether metric or US units are used.
The File Settings item on the Telemetry page allows the filename and method of activation to be set for data logging. See page 8.
The various display fields are generally self-explanatory but there are some differences between Spektrum and Lemon telemetry. In particular the Lemon receivers do not offer the Fade, Frame loss or Hold information used by Spektrum to display receiver functioning.
Instead, using the Spektrum Flight Log display page, Lemon provides a single RSSI number in the “A” field that shows received signal strength on a decreasing scale ranging from 100% to about 20-30%. At this point, telemetry will normally drop out, but solid control will be maintained well beyond this minimum value.

When the receiver is first powered up, the firmware version code is briefly displayed in the B, L and R fields, as shown in the screen shot at right. B = Year, L = Day and R = Month.
Assuming that the voltage wire is connected to the flight pack battery positive OR the V/I sensor is installed in the main power cable, the first Telemetry screen should show Flight Pack Volts. If the flight pack battery Volts field does not appear, you may have to select it manually in the Telemetry setup screen and change some other display field to Volts. Temp displays the receiver processor’s internal temperature. RPM is not used.
The second Telemetry screen will display the Altitude and, if a V/I sensor is connected, the flight pack current (Amps). The Speed field is not used.

The Flight Pack Capacity screen uses the Current (Amps) reading from the optional V/I sensor to measure the usage of battery Capacity in milliampere- hours (mAh). The display is set to zero when the receiver is plugged in and counts up as power is consumed (very slowly when the receiver is idling). This screen also displays Imax, the maximum current to this point in the flight.
There may be one or (as shown here) two Flight Pack Capacity displays. Only the first is valid. The Temp fields on this screen are not used by Lemon telemetry.

The Vario display presents a graphic readout of Vertical Speed over a chosen period of time. However, the most useful vario output for glider flyers is the audible variation in tones as the model rises and descends. This must be activated in the Telemetry (Auto-Config) screen under the Vario item.5
This screen also includes an Altitude number, the value of which may differ slightly from that displayed on the Altitude/Amps screen. This is of no practical significance and either value may be used.

The altitude displayed is Above Ground Level (AGL). The altitude should automatically reset to zero when power is applied, but due to atmospheric fluctuation a small negative value for Altitude is often displayed while on the ground. 6 It is recommended to press the “Clear” button to reset the Altitude reading to zero before flying.
The Min/Max screen gives a summary of high and low values recorded during the flight. You may get an unrealistic value for Minimum Altitude when first connected, but this can be reset by pressing the “Clear” button.

5 Users have noted that the Lemon Vario setup may be more sensitive than the equivalent Spektrum system.
6 On some Spektrum transmitters the reading may just fluctuate around zero. In that case, use the main Altitude field.

Telemetry Log Files

Spektrum telemetry-enabled transmitters can record on the SD card a log file of the data sent to the transmitter by the receiver. This is controlled entirely by the transmitter; no receiver setup is required.
The options available at the transmitter specify whether recording is enabled, if so, how it is to be started, and the name of the resulting file. Refer to your transmitter manual for specific instructions. You may want to assign a switch to start and stop logging, or you may prefer to have it start automatically as soon as the throttle is advanced. One commonly used arrangement is to have logging controlled by the Throttle Cut switch, thus activated whenever the motor is ON.
The log files are saved on the SD card plugged into the transmitter. The log files have the same name as the corresponding model files but with an extension of .tlm rather than .spm. To read Spektrum log files you need a program specifically designed for the purpose. The excellent and versatile Tlmviewer program was written by modeler Mike Petrichenko. This is a free Windows-only program. Contributions are suggested. There is no available program that works with current MacOS.
Here is an example of the Altitude readings from a flight log of a motor glider. The log from the SD card is read and graphed by Tlmviewer. Altitude (here in meters) is shown on the Y-axis, while time is on the X-axis. There is a great deal of flexibility as to which variables are plotted and how they are presented on the graph.
It is also possible to export data from Tlmviewer as a .csv file and then import into Microsoft Excel, where it can easily be displayed in various alternative formats.

Annex A: Voltage and Current Calibration
Two types of sensor are available for use with the Lemon RX Telemetry Receivers to measure the flight battery parameters in an electric powered model: the Voltage Sensing Wire measures only Voltage while the V/I sensor measures both Voltage (V) and Current (I).
The Lemon Rx sensor used must be matched to the specific receiver. Recalibration of the receiver, as explained below, is needed whenever a different V/I sensor is paired with a receiver, or when an installation changes from V/I sensor to a voltage sensing wire or vice versa.
NOTE: You do not need to do any recalibration if you are using the sensor (V/I or voltage sensing wire) that came supplied with your Lemon stabilizer. Factory calibration is sufficiently accurate for all normal purposes.
Voltage wire sensing recalibration is relatively simple but V/I sensor calibration requires some care and effort.
Any time you change to a different V/I sensor, or between V/I and wire, however, you must carry out this procedure, as the calibration is individual to each sensor and is stored in the receiver.
Bottom line: If you change from the sensor supplied with your receiver you must recalibrate.
The following sensors are available from Lemon RX for the 7 and 10 channel Telemetry Receivers:

• 60 Amp, 26 Volt Voltage and Current sensor with XT60 or T-Plug connectors
• 130 Amp, 26 Volt Voltage and Current sensor with XT90 or EC5 connectors
•  LiPo flight pack voltage sensing wire.

Note that Spektrum™ sensors cannot be used with the Lemon-RX receivers.
Recalibrating the Receiver for the Voltage Sensing Wire
For calibrating the voltage sensing wire, you do not need any measuring instrument, just a regular, fully charged 2S-6S LiPo (not an HV LiPo pack), which will provide 8.4V on the balance lead from the second cell. 7
Procedure

1. Connect the voltage sensing wire to the positive side of an 8.4V source. A fully charged 2s LiPo battery will provide an adequately accurate reference voltage. The negative side must connect to the ground of the receiver power supply. An alternative solution is to use a fully charged flight pack of 3S or more and connect the voltage probe wire to the 8.4V (2S) socket on the balance connector. The small current drawn by the receiver in the few seconds it takes to do the calibration will not change the fully charged cell voltage appreciably.

2. To enter Calibration mode, press buttons B and F simultaneously and hold down for about 5 seconds. When the 3 green LEDS start flashing, release B and F. Don’t hold down much longer than that, as the receiver will eventually go into Factory Reset mode.

3. While the three green LEDs are flashing, press the C button briefly (less than 1 second). A change to three red LEDs blinking means the voltage reading is calibrated. The telemetry screen should display either 8.3V or 8.4V as flight battery voltage, 8 with 0A for current.
   7 The receiver supply must be 5V, as the Rx voltage value in the telemetry is calibrated at the same time as the flight pack voltage. You cannot use a 6V BEC, or a 4.8V, 6V, 6.6V battery, or any other non-5V source.
   8 Note that 8.39v will display as 8.3v because of the lack of a second decimal digit in the Spektrum transmitter display. The more precise value is used internally and can be logged.

4.  Press B to complete voltage calibration. This is necessary to save the calibration value. Just turning off the receiver will NOT save the calibration.

If you want to check that the calibration voltage is correct, you can use a wattmeter in-line with the LiPo (as shown in Hookup – see page 10) or you could use a separate voltmeter to check the battery voltage. However, for purely voltage calibration this is really unnecessary if you are confident that your two-cell LiPo is fully charged.
Note that if the receiver comes with a voltage sensing wire, it is already calibrated to use that sensor.
Recalibration as described here is only necessary if the receiver was previously used with a V/I sensor.
Recalibrating the Receiver for the V/I Sensor
Recalibrating a V/I sensor is more involved, but an adequate calibration for the V/I sensor can be performed using a two-cell (2S) fully charged standard 4.2V/cell LiPo battery and a quality electric model Wattmeter. However, a regular DVM with a DC Amps range that covers 4A may be more accurate for the current calibration and can replace the Wattmeter. As explained below, during calibration the receiver must be powered by an ESC or BEC delivering 5V.
Hookup
Hook up the sensor and other components as shown below but leave the battery disconnected for now. The 2S LiPo battery will provide the necessary 8.4V for the voltage calibration and approximately 8V under load for the current calibration. 9

The photo at right shows a hobby quality Wattmeter in use to display voltage and current; you can also use an Ammeter in series provided it can measure a current of at least 4A. The more accurate your measurement, the more accurate the calibration.
Ensure that the sensor connects directly to the 2S LiPo battery and that other connections “downstream” are reasonably short and capable of carrying the 4A current to the motor. This is important to avoid an unacceptable voltage drop, which would affect the accuracy of the calibration. Avoid long, thin leads to the Wattmeter (or Ammeter).
Use an ESC with 5V receiver output. 10 Plug the throttle connector into the throttle channel pins (channel 1). If the ESC lacks an internal 5V BEC, a separate 5V BEC can be used to provide receiver power via another set of pins; any available set of pins can be used for this except BEC1 or BEC2. 11
9 The battery needs to be able to supply a 4 Amp current without undue voltage drop. It is recommended that the battery be in good condition and have at least 1000 mAh capacity and 20C or higher rating. Although 8.4V is used for the voltage calibration, once  you connect the load and throttle up to 4A it is unlikely the LiPo will do better than 8.0-8.3V while supplying that current. This doesn’t matter for the current calibration part as long as the sensor sees a steady 4A.
10 The receiver supply must be 5V, as the Rx voltage value in the telemetry is calibrated at the same time as the flight pack voltage. You cannot use a 6V BEC, or a 4.8V, 6V, 6.6V battery, or any other non-5V source.
11 Using pins BEC1 or BEC2 would introduce an error because of the isolating diodes used on those inputs.
To provide the correct current for calibration of the sensor, connect the ESC to a motor that is known to draw at least 4 amps. It may be necessary to install a propeller to create the necessary load – if you do this, be VERY careful to ensure that the motor is safely mounted.

Procedure

1.  Power ON transmitter and receiver. To enter Calibration mode, press buttons B and F simultaneously and hold down for about 5 seconds. When the 3 green LEDS start flashing, release B and F. Don’t hold down much longer than that, as the receiver will eventually go into Factory Reset mode.

2. Verify that the three green lights on the receiver are still blinking. Test that the motor runs in response to the throttle stick and that a steady 4A current can be achieved

3. Once sure that everything is working, throttle off, power down, and recharge the 2S LiPo to a full 8.4V.

4. Power ON the transmitter and plug in the battery to power the receiver.

5. Re-enter Calibration Mode as explained in 1.

6. While the three green LEDs are blinking, press the C button briefly (less than 1 second). A change to three red LEDs blinking means the voltage reading is calibrated and current sensing bias is set at 0A. The transmitter telemetry page should display either 8.3V or 8.4V as flight battery voltage, 12 with approximately 0A for current before throttling up.

7. Move the throttle stick to start the motor (be careful!) and adjust until the current draw is as close as possible to 4.0A. The photo at right shows this moment (the red LEDs in the photo should be assumed to be flashing).

8. With the system still drawing 4A, check that the telemetry screen shows a current reading of 3 or 4A.13

9. To cancel or start over at this point, press the C button.

10. To complete voltage and current calibration, press the B button until the LEDs stop flashing. Just turning off the receiver at this point will NOT save the calibration.

11. Of course, be sure to disconnect the motor when finished calibration!
    Don’t forget to re-bind the receiver (with satellite attached, if used). Reset Failsafe to suit your model.

12. Note that 8.39v will display as 8.3v because of the lack of a second decimal digit in the Spektrum transmitter display. The more precise value is used internally and can be logged.

13.  Note that 3.9A will display as 3A because of the lack of a decimal digit in the Spektrum display; this 1A precision is ample for most purposes. The more precise value is used internally and can be logged.

Annex B: Options for Attaching the Voltage Sensing Wire
To measure the voltage of the flight pack in an electric-powered model using the voltage sensing wire, there are three basic options. They all have pros and cons. Use the one that suits you best.
Note that the receiver may need to be recalibrated to use the wire.

Option 1: Insert Single Pin into the Balance Connector
This is the default and most convenient. Use the pin on the end of the voltage probe wire. It will fit into the highest voltage wire on the LiPo balance connector. The JST-XH balance connector used on most batteries will accept this pin correctly.

Pros

• Can be used in any model. The balance cable is always there.
• Neater and smaller than using a separate female balance wire connector.
• Works with a pack having any number of cells.

Cons

• Least secure option – but it’s not flight critical if it comes off.
• Plugging into the wrong wire will give a misleading reading (but won’t hurt anything).

Option 2: Attach Wire to the Main Power Lead
Cut off the pin on the voltage sensing wire and solder the wire directly to the mapositive (red) feed to the ESC or BEC.

Pros

• Fit and forget. Every time you plug in a flight pack you automatically get telemetry voltage.
• Rugged. The heat shrink and heavy duty power wire make it a very secure connection.
• Works with a pack having any number of cells.

Cons

• The voltage sensor wire is permanently attached and cannot be swapped around.
• Requires soldering to the main power wiring on which everything depends.

Option 3: Attach via a Socket to the Balance Connector
Resolder the voltage wire to the positive wire of a female JST-XH balance connector socket with the appropriate number of pins.

Pros

• Reasonably secure as the connectors clip together.
• Can be used in any model. The balance cable is always available.

Cons

• A bit clumsy and vulnerable.
• Only works for one cell count (unless you add multiple balance connectors).

Option 1 is flexible and neat but any of the three will work just fine. If the receiver is expected to stay in the model for the long term, Option 2 may be preferable.

Annex C: Understanding RSSI

The Lemon RSSI (Received Signal Strength Indicator) number is sent back from the model by telemetry and displayed in the “A” field on the transmitter screen, as shown in the photo of a Spektrum DX8e screen.
RSSI represents the strength of the radio signal available from the receiver front end for control of the model. It should read close to 100 when the transmitter is next to the model and drop with distance until, at a value typically around 20-30, the telemetry signal is no longerstrong enough to convey the data and the display freezes. As the receiver has excellent sensitivity, reliable control will continue well beyond this point.

The vertical bar symbol in the top left of the photo shows that telemetry is live and being received. In this case the bars are at zero and indicate that the telemetry signal is soon to be lost. Compare with the full-strength Telemetry signal bars in the pictures on page 7. Depending on the transmitter and software the number of bars may give an indication of the telemetry signal strength.
Changes in the RSSI reading can be conveniently explored with the transmitter in Range Test mode. Note that putting a Spektrum transmitter into Range Test mode attenuates output power enough to reduce range by a factor of about 30. 14 Thus effective control at 35m (115 feet) in Range Test mode (which should be easily attained) should translate to about 1 km (3600 feet) range at full power. There are, however, many variables involved, so treat this as only a rough guide. There is a very good probability that  you will get much greater range than this.
The Lemon RSSI number is a relative value and cannot be directly compared to other signal indicators such as antenna fades reported by Spektrum or the FrSky RSSI number. Lemon has stated that the maximum signal measured after the LNA front end when the transmitter and receiver are right next to one another is displayed as a value of 100. A drop in “RSSI” by one unit corresponds to a drop in signal strength of approximately 0.6dBm. At the Lemon recommended minimum reading of 20 the signal is therefore 0.6 x 80 = 48dB down. While the receiver has a lot of reserve sensitivity and should continue to work even beyond that point, it is not recommended that this be taken for granted.
14 Since range is related to the square of power, to reduce range by a factor of 30 requires a cut in power by a factor of about 900. Range test power is thus typically around 0.1 mW, compared to full power value of around 100 mW.

Telemetry with the Lemon Rx 7- and 10-Channel Receivers R1.docx

References

• Spektrum Telemetry Log File Viewer
• RC Groups
• RC Groups

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