Review: Frsky R9 Slim Receiver For Long Range

The FrSky’s R9 receiver is designed to work with the Frsky R9M long range module, however it was just a bit too big for mini quads. Therefore Frsky made a smaller version, the R9 Slim, which we will check out in this review.

You can get R9 Slim from HorusRC. This review is written by Artur Banach.

Further Reading: How to choose radio transmitter and receiver?

Features of R9 Slim Receiver

  • Designed for the Frsky R9M Long Range TX module
  • Much smaller than the original R9 Receiver
  • Two frequency available: 868MHZ for EU, 900MHZ for non-EU
  • Redundancy function
  • Supports SmartPort Telemetry
  • Dedicated RSSI Output
  • Theoretical Range: 10Km+

The R9 Slim RX has two JST connectors:

  • 6 pin, on top, for SBUS and voltage in
  • 8 pin, at the bottom, for servo channels

Wire harnesses come with the receiver.

From the pinout diagram, we can see that there is a SBUS_IN pin for connecting second receiver for redundancy, as well as a dedicated pin for RSSI output.

R9 Slim comes with dipole antenna with u.fl connector.

Antenna active element has 82mm of length. Receiver and transmitter antennas are meant to be set to vertical orientation for maximum performance according to FrSky,

Configurations and Options

When shopping for the R9 Slim receiver, you have to choose one of the two versions on the product page:

  • EU LBT (Europe) 868mhz
  • FCC (International) 916mhz

Or you can flash the firmware to get it working in the frequency you want (firmware available on FrSky’s website).

The power options for the EU LBT firmware are:

  • 25mW (8 channels with telemetry or 16 channels without telemetry)
  • 500mw (16 channels without telemetry)

FCC power settings (all with 16 channels with telemetry):

  • 10mW
  • 100mW
  • 500mW
  • 1000mW

Notice that the EU LBT version is more limited compared to FCC. According to FrSky that’s because of the harder restrictions of EU regulation regarding radio transmission power.

You need to bind your receiver again every time you change transmitting power or mode.

There is however a bug in OpenTX when using EU LBT. Before selecting 25mW mode with telemetry you have to switch the R9M to FCC and check the option “Module telemetry”. Once that’s done you can switch R9M back to EU LBT and bind with the 25mW mode.

I have some tips about long range flying you might find useful.

R9 & R9 Slim vs. Crossfire Micro & Nano RX

Here is a comparison table between the different popular long range receivers for their sizes, prices, and features.

Further Reading: How to setup Crossfire in Betaflight?

R9 Slim R9 Crossfire Micro V2 Crossfire Nano
Price (Feb 2018) $25 $50 $45 $40
Size (mm) 30 x 14 x 5 43 x 27 x 14 40 x 14 x 9 11 x 18
Weight 3.2g 15.8g 3.3g 0.5g
Voltage 3.5-10V 3.5-10V 5V 5V
Current [email protected] [email protected] N/A N/A
SBUS ? Yes Yes CRSF / SBUS CRSF / SBUS
Smart Port Telemetry ? Yes Yes Yes Yes

The R9 Slim receiver is a bit shorter than Crossfire Micro RX V2 and much smaller than R9. (Sorry I couldn’t show a comparison between the R9 and R9 Slim as I’ve broken the R9 receiver)

Performance

I have been testing R9 Slim receiver for about 6 weeks. Receiver was being regularly flashed with latest firmware available to keep it up to date.

My testing setup:

I soldered the RSSI wire on the receiver to the Matek RSSI pad to get RSSI displayed in OSD regardless of whether I have telemetry or not. I only tested the EU LBT firmware because I’m in Europe.

I flew the quad in a big open field with few patches of bushes and some trees. The field is about 1km long and 800m wide.

I tested both power settings:

  • 25mW with telemetry
  • 500mW with no-telemetry

In both power settings, I flew 1km out and there was no signal dropouts, although RSSI value was jumping between 60 and 98 constantly while I was at the end of the field. There was no failsafe or any noticeable issues with the radio link, even when I was flying behind trees at distance. Latency level feels similar to the Crossfire, I didn’t notice the difference personally.

Good things about R9 Slim

  • Small form factor – suitable for mini quads
  • Affordable option at only $25
  • Good selection of power settings with telemetry in the FCC version
  • The dipole antenna is easier to attach on a mini quad compared to the R9 receiver
  • RSSI out pin for convenience

Things to improve

  • Inconsistent RSSI readings hopping during the flight. Could be a firmware related, but this definitely needs FrSky attention
  • Poor selection of power settings for EU LBT version. Only 25mW with telemetry. R9 Slim FCC version feels like a better version of the same product
  • Telemetry only shows RSSI and Receiver Voltage Input sensors
  • It would be nice to allow frequency selection in the setting without flashing the firmware, like in the Crossfire. But it’s not that a big deal since most of us don’t travel around the world with our models

Conclusion

It’s great to see there is a smaller FrSky receiver dedicated for R9M long range module for mini quads. It performed well in my tests but there is certainly room for improvement, especially regarding RSSI value and power options for the EU LBT version.

27 thoughts on “Review: Frsky R9 Slim Receiver For Long Range

  1. bobby

    frsky can propably only satisfy eu law with lower power settings. we should ask them about an ham firmware for the transmitter module so they can legally provide all power and telemetry modes on 868 mhz.

    Reply
  2. Pete

    Hi bit of a noob question are the fcc and eu r9m modules the same ? Is it just a case of a firmware update if I have an e17 module and want to use the fc features

    Reply
    1. Oscar Post author

      The different firmware operates at different frequency.
      Yea you can switch between FCC/EU by flashing the firmware.

      Reply
  3. Christopher

    what do i need to do to get PWM output to work on my R9Slim FCC version? the binding method for SBUS does not do the trick, i have completely removed the sbus plug and wired up using the PWM’s

    Reply
  4. David Rogers

    Oscar, does it matter when placing the antenna in the L position which antenna is vertical? The clear or the black coated?

    Reply
  5. Patrick

    A comment mentioned L is the optimal antenna shape. That’s not just totally wrong, but also dangerous. A dipole antenna, like the R9 system is using has a quarter wavelength on TX and RX antenna, which has to “hit” the antenna in a straight line (T shape) to get full resonance and signal strength.

    Reply
    1. Pavan

      Hi, By T shape you mean 180 degrees apart ? Should it be placed horizontal or vertical to the ground? Thanks

      Reply
  6. Chuck Gillespie

    Oscar, Have you had a chance to compare the FRSky R9 Mini to the Crossfire. It is much less expensive.

    Reply
  7. David

    Telemetry only shows RSSI and Receiver Voltage Input sensors?
    is this still true? can not show like gps, amp draw, flight mode with iNav?
    How about the r9 mini, is it the same? no gps telemetry info?

    Reply
    1. Ricardo Maroquio

      You have telemetry parameters if your source can transmit in S-Port or if you use a special cable that converts MavLink to S-Port.

      Reply
  8. CARLOS GRIJUELA

    Oscar…please only one question
    in frsky x9 slim how you instalation de dioole antenna? in T possition or in L or 90°..I dont know how put this model of antenna..

    I have de r9m module and I I’ve noticed some cut in 1w self adaptive model in FCC model … maybe it’s the antenna or the receiver’s consumption.?

    Reply
    1. Oscar Post author

      L is the optimal position, you get some signal lost with T position (acceptable level), but some people prefer that because it’s easier to mount.

      Reply
  9. noah hansen

    Are you able to get an un-inverted smart port signal by soldering to some pin on this board? or can you only get the regular inverted smart port signal from the JST connector?

    Reply
    1. Javier

      I do also have this question it would be good to know from where to get the un-inverted S.Port or another way to get Telemetry on BF for F4 boards with this R9Slim receiver?

      Reply
  10. Badr

    is there a way to have RSSI displayed in the osd without soldering ? like we actually do with a regular xm+?
    Also, is the R9M able to switch as well between EU version and fcc?

    Thanks.

    Reply
  11. Enrico

    finally the first review available for this receiver after so long!
    thank you!!
    Question:
    you soldered RSSI pin directly to the FC. I was thinking this method never worked accurately as in some case you need to install resistors (this is what i’ve being told when i did the same with a FrSky receiver).
    Are you sure that the rssi fluctuations were not due to voltage spikes, noise or even voltage range issue related to this type of connection?

    i really would like to upgrade to a more robust connection from my actual XSR but investing so much money in the TBS system seems to me crazy although the new nano receiver is now pushing the boundary again.

    Reply
    1. Artur Banach

      It took a while before I gathered conclusions. I have soldered RSSI directly to Matek F405-CTR because this was I could see RSSI on 500mW Non-telemetry mode. If it’s causing issues than it’s another point they could make an improvement on

      Reply

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