Sombra Labs - SL-8 and Lepton-6 Receiver Review

The latest in receiver technology is tested to its limits in a complete test of range and abilities in maintaining a solid radio connection.



Lepton 6
Dimensions:38 x 15 x 12 (mm)
Weight:7g (with antenna)
System:Single Conversion with DSP
Channels:6 (12 in series)
SL 8
Dimensions:37 x 20 x 12 (mm)
Weight:9g (with antenna)
System:Dual Conversion with DSP
Channels:8 (16 in series)
Manufacturer:Sombra Labs
Available From:Sombra Labs or...
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Price:Lepton 6 - US$34.99
SL 8 - US$64.99

The advanced technology we hold in our hands that provides us the ever required connection to our radio models is the key ingredient in the recipe of "radio control". Newer and better systems are introduced all the time. As part of my own search for more advanced radio system, I bought a package with a Futaba synthesized transmitter module and went looking for receivers to match.

The system came with a synth receiver too large for my smaller models, and with full range receivers for 72MHz being so small and capable, my expectations were a lot higher for a small receiver. Enter Sombra Labs which currently offers two receivers: the eight channel synthesized SL8 and the six channel crystal based Lepton6. Both receivers are really small and light (said to be the lightest on the market for their respective channel count), full range, ultra narrow band (5kHz or better) and have advanced digital signal processing (DSP). Since I have an interest in micro helis (that happen to need 6 channels and light equipment), both of these receivers were worthy of a close look.

The Receivers

Lepton 6

This small receiver is crystal based, single conversion, six channels and certainly lives up to its claim to size and weight. It uses UM-1 crystals that you can order from Sombra Labs for $6 (Berg crystals will also work). An optional extra is the Shadow Programmer that is required if you need to fiddle with the advanced features. However, the receiver’s stock setup has all the good stuff turned on, so in most instances it is only a matter of plugging in your crystal, putting a piece of tape over the crystal to ensure it doesn't fall out, and heading to the field.

 what's in the pack
what's in the pack
 a great receiver
a great receiver
 with programmer plugged in
with programmer plugged in


The larger of the two, it has two more channels (making 8), dual conversion signal processing and uses a synthesized system instead of a crystal for channel selection. Like the Lepton6, you can use the shadow programmer to tweak its internal settings, however, it does have the ability to automatically scan and lock on to your transmitter's frequency without one. As easy as the auto-scanning is, my preference is to play with the programmer simply because it has dials (yes, dials)! It makes things nice and obvious: dial the channel in your transmitter, dial the receiver, job done.

Only slightly more involved is the automatic frequency scanning. By plugging in the provided loopback plug into channel 8 and cycling the power, the process is started. The receiver indicates that it is scanning by making small oscillations with the servos (note: while in this process do not move transmitter sticks or switches). When the servos stop, the process is complete. Confirm that it has the right channel my moving your transmitter sticks. Remove the loopback plug and cycle the power. Now you're ready to fly.

 what's in the pack
what's in the pack
 a great receiver, less crystal
a great receiver, less crystal

Single / Dual Conversion?

At a basic level, conversion is simply the processing of the input signal into the signal used internally to speak to the rest of the system. The only problem with single conversion is that an image of another frequency can confuse the signal. Dual conversion improves upon this by processing the signal twice before interpreting it for use in the system. This greatly improves the ability to filter out unwanted noise.

However, it should be noted that single/dual conversion doesn't fully represent bad and good receivers. Some very good receivers are only single conversion yet have advanced digital signal processing (DSP) to filter out the good from the bad. A dual conversion receiver simply means that it has a leg-up on the noise filtering game.

Common Features

The common features shared between the two receivers:

  • Full range. Ultra narrowband (5kHz or better)
  • Smallest and the lightest receivers in the world for their respective channel count
  • Excellent sensitivity and IP3 performance
  • Can be programmed through a modular and easy to use programmer utilizing Sombra Labs' patented "1-Click"(TM) programming technology
  • Three user selectable and programmable fail-safe modes
  • Compatible with most of the FM/PPM transmitters
  • Automatic positive/negative transmitter shift detection
  • Fully programmable servo pin assignments, any servo pin can be made to output any channel
    (from channel 1 to 12 for the Lepton3, to 16 for the SL8)
  • Ability to store two user "Servo pin-to-Channel" assignments
  • Cascade mode: link two receivers to double the channel count
    (yes, the SL8 can be a 16 channel Rx and the Lepton6 can be 12 channels!)
  • Most advanced DSP signal detection, noise control and glitch suppression algorithms
  • Ability to turn the DSP filtering on or off using the Sombra programmer
  • Fully FCC / IC (Industry Canada) compliant.
  • Horizontal and Vertical pin configurations
  • Designed and manufactured in Canada

The Shadow Programmer

If you need to dig deeper on the trickier settings, this is the little device required. The idea behind the Shadow Programmer is that all settings in the receivers are represented by a number. The two dials represent the number of the setting where the left hand dial stands for the "tens" and the second dial is for the "ones". To set channel 39 on the SL8 receiver, select 3 on the left dial, and 9 on the right hand dial.

To store the setting into the receiver you simply turn on the receiver, plug in the programmer (with the number dialed in) and push the button on the end of the programmer. An LED will light up on the end of the programmer to indicate that the setting has been made. If you need to change more than one setting, you can leave it connected, redial the next number and repeat the process.

The channel numbers for the SL8 are all straightforward; the face value is all that you need. The other settings of the receivers have a table of numbers that can be found with the instructions provided with the receiver. The same shadow programmer works for both receivers and was actually introduced with previous products so its usefulness probably wont stop at these receivers.

 the dials in place
the dials in place
 ready to program my SL8 to channel 39
ready to program my SL8 to channel 39

Setup And Configuration

For basic use, these receivers are like any other: plug the servos in and go play. Because the SL8 is synthetic, it does need to get the right channel before it can do the flying dance. The Shadow programmer is easiest method to select the right channel, but the automatic scanning isn't all that far behind in terms of convenience.

For most uses this is all you need to know, however with the Shadow Programmer you can change some more advanced features. These features include the fail-safe settings, complete channel/pin mappings (change which pins handle which channel) and to turn off/on digital signal processing (DSP). The latter struck me as interesting: why would you want DSP off? The answer to this from Sombra Labs is that it's for use with buddy-box systems. DSP includes processing that identifies your transmitter and ignores other signals. With a buddy box system, you are literally changing the transmitter generating the signal, so if the receiver is locked on to one it will ignore the other. The Sombra Labs receivers can turn this off so you can use the buddy-box system without problem. Turning off DSP is also also handy to mitigate radio problems - removing DSP from the equation makes problems more apparent.

All the programming and setting changes that I made with the receivers were straightforward and to the description of the instruction sheet. Before flying I returned the receivers to stock form. They came ready with all the right ducks in all the right rows.


For something that is responsible for 50% of the connection equation, we typically don't put the whole system through much of a test. A basic "antenna down" range check is all that most receivers get to prove themselves before aviation happens. The pity is that "antenna down" doesn't tell the full story. Systems can perform well with this test and yet have failures in actual use, so my intention for the review was to cover the receiver abilities with a fully extended transmitter antenna, and ideally, to target the different aspects and abilities of the receivers.

The intentions of the tests are to cover:

  • full range testing
  • range testing with trimmed/coiled receiver antenna
  • noise filtering
  • transmitter recognition

Range Testing

Performance of radio equipment in general is described in terms of "clear line of sight". This is important for extended antenna tests, yet was a problem for me specifically: Central Pennsylvania doesn't do "flat" very well. However, there was a valley that on one side has a full-size airstrip that was available. The plateau this airstrip sits on is about the same elevation as the opposite hill. The plan was to put the receivers on the opposite hill, and then run the range test out and along the airstrip. Distance from the receiver station to the far side of the airstrip is a touch over two miles.

The Setup

The objective of the equipment setup was intended to reflect an actual model setup: the receivers were mounted to a base and the antennas strung along some spruce spars. Servos were added to the base with some balsa arm extensions so movement could be easily observed. Power was added by way of LiPo batteries through some speed controls and their onboard BECs. The antennas were vertically mounted off the ground away from any obvious interfering objects.

The test was completed by turning on the receivers and transmitter and confirming the connection, followed by jumping in my car and driving out the range test - the transmitter antenna fully extended the entire time, the system working in all its glory. At each test point I called a helper sitting with the receivers (by way of mobile phone) to verify the action of the servos against my input. This was repeated for each test point during the range test for both receivers.

To help out with measuring distances, EagleTree Systems graciously supplied a GPS unit for my V3 logger. Perfect for this use as true line of sight would not be needed and recorded data can be gathered and analyzed a later point. The GPS data could also be plugged into Google Earth to give pretty graphics and viewing. All that had to be done was to turn it into a "hand-held" version by the addition of power source, the GPS unit and the LCD screen.

Following is a Google Earth screenshot of the GPS tracking to help illustrate the path taken and how the test was completed.

Basic Range Test

Station A - distance to station: 0 feet (0 miles)

System was working solid with both receivers, no great surprise there.

Station B - distance to station: 6,450 feet (1.22 miles)

The end of the airstrip is more or less on the same level as the receivers, although true line of sight was blocked by trees and maybe a doublewide or two. The purpose of this stop was to verify that after crossing the hollow that there was still positive reception. A call back to base confirmed that the receivers were locked-in with positive movement on both servos.

Station C - distance to station: 10,550 feet (2 miles)

While this station was clearly not line of sight (undulations in the land and a slight curvature over the plateau meant there was no way to physically see the base station), it was the longest distance I could travel before going downhill significantly. The reception was still locked-in and very positive for both receivers in my call back to the base.

Station D - distance to station: 12,025 feet (2.27 miles)

Line of sight was clearly destroyed at this point, and I was looking at turning around. I called base and retested for the sake of good data. There was no reception by either receiver, however this was clearly well below the ground line as set up by the airfield. I wasn't surprised; this is included for the sake of a complete story.


The receivers reached the full distance of the range test that I could perform with "near enough" line of sight with the lay of the land as it was. Even as it stands, two miles without true line of sight is quite a distance. It is certainly well beyond anything I've flown including specking-out large thermal soarers. Sombra Labs tells me that true line of sight range is around 4 miles. While I have no reason to doubt them, one could be forgiven for feeling the distance between the 2 and 4 mile markers is trending towards the academic.

Trimmed Antenna Testing

There was a reason for "Station E" in the course chart above: it did indeed have a true and clear line of sight. This spot was ideal for performing a test of trimming the receiver antenna wire. The reason for this test is simply that many people trim the antenna wire to suit a particular setup or to reduce weight, so I felt the need to see the impact of this on the range. Many people also coil the extra length inside the plane (in fact this is recommended over trimming) but the results are the same. Coiling the wire will effectively shorten the antenna to the length that is the distance across the coil (see photo below).

Trimming the antenna to a different length (either rolling coils or cutting the wire), should be done in fractions: 1/2, 1/4, 1/8, etc. Reason being that the antenna length marries to the wavelength, and trimming in these fractions will help the receivers in reading the signal.


Station E - distance to station: 6,875 feet (1.3 miles)

  • 1/1 - 39 inches - It was no surprise that it worked at full length when I arrived at this station.
  • 1/2 - 19.5 inches - Both receivers locked-in and smooth.
  • 1/4 - 10 inches - Both receivers locked-in and smooth.
  • 1/8 - 5 inches - Lepton6 - locked-in and smooth. SL8 - still working, but now with the odd hesitation
  • 1/16 - 2.5 inches - Lepton6 - working but with hesitation. SL8 - not working

Trimming Results

I think these results almost speak for themselves: Solid reception with 1/4 length at 1.3 miles is awesome. Lepton6 improving on this to be solid with 1/8th the antenna wire and the fact that the SL8 was getting any at this point is impressive. Truly astounding is that the Lepton6 was reading signal at 1/16th the antenna length, just 2.5 inches of antenna wire!

Noise, Noise, Noise!

Filtering out non-transmitter noise is another important job receivers have to deal with. Some great noise makers are present in our planes, especially electrics: motors, motor wires and speed controls are noise generators to some degree. There really is a reason why manufacturers give warnings against lengthening motor wires and tell you to put some distance between these components and your receivers. Even metal-to-metal control connections can generate a resonance that will create radio interference if allowed to hit the right harmonic.

The Setup

To test out the noise filtering abilities of these new receivers, I exaggerated the warnings of these manufacturers... in the wrong direction. I'm sure that this will become the model for "how not to setup a receiver, brushless motor and speed control". The motor wires were lengthened a couple of extra feet, and literally wrapped around the receiver. To cap it off I left the speed control sitting underneath and taped it all to a board. The motor connected to the rig had a prop mounted as to create some load on the system, therefore increasing watts and with that some RF noise.

While there may be a better way to create RF noise, this was certainly the most invasive that I could come up with.


In using the system, it was almost as if there were no noise at all. The noise had an effect on range based on the fact that the antenna down range test was reduced by about half, but I still made it a passable distance away from the rig. However with the antenna partially extended I was able to get to the other side of my field (750 feet) and was in solid contact with the receiver. Both of these receivers were the same in this respect. As a verification that it was a significant test to overcome, a cheaper/older receiver was brought to its knees when placed in the same conditions.

Transmitter Recognition - Digital Signal Processing (DSP)

Receivers of the past simply go crazy when there's more than one system transmitting on the same frequency. This was naturally because it couldn't tell the transmitter signals apart. The invention of Digital Signal Processing (DSP) does a few things (like helping the noise filtering in the test above), but one part of its box of tricks is identifying transmitters. When you turn on the receiver, the first thing it does in processing the signal is to come up with a signature for the signal. Any signal from a different transmitter will then be ignored.

With the same test setup rig on the bench in the field, I walked out one transmitter and then turned on another with the same frequency. I used the Futaba 10C and Futaba 7C, and I alternated them being the first "locked on" transmitter.


The first thing you see is that the receivers are clearly ignoring the signals from the "other" transmitter. The DSP clearly singles out the initial transmitter, as nothing you do on the second transmitter will move the servos. However there is a negative effect on the initial signal. If the second transmitter has more signal strength it can effectively shut down the connection between the initial transmitter and receiver. If the initial transmitter is closer to the receiver, then it will be as if the second transmitter was never turned on.

The result is that if someone turns on their set while you're at the flight line and they're back in the parking lot, then you may not even notice their system was on. Impressive stuff! However, if the second set is near the flight line and you fly a low pass next to him, then your connection to the plane may be shut down.

Most shoot-downs are casual happenings without the antenna being extended at all (turning on the set to check a setting, or to confirm some setup with a plane), and for these cases you will most likely not even notice. I was hoping to report the "you wont notice at all" scenario, but it is clear that a second set can cause genuine problems for the main signal. That said, I do feel that improving the situation from "certain crash" to "it's possible you may not even notice" is outstanding, and a true sign of the technology in these modern receivers.


The truth of all the above testing was that it was all done after I had flown the receivers. Just like all other receivers/radio setups I connected the servos, did the antenna-down range test and went flying. The link to my models has been steady and reliable. The only hiccup was my fault: In my haste I forgot to put tape over the crystal in the Lepton6 and when entering a violent spin the crystal managed to fall out. The plane survived just fine so I mounted the SL8 in its place and kept flying. The Lepton6 was put back into service in another model by way of a spare crystal I already had.

If you tape in the crystal, or if you use the SL8, your flying will be truly care free (well... with respect to the radio link at least).

Is This For A Beginner?

A beginner can feel confident in using these receivers out of the box. The fact you can happily use these in a buddy-box setup will confirm they are ideal for trainer setups. As time goes on, beginners may even enjoy playing with some of the advanced features too!


With respect to the range testing and use of these receivers one couldn't be more confident in the solid connection. It was interesting that the single conversion Lepton6 marginally outperformed the dual conversion SL8 in the antenna-trimming range test, and that it did just as well in the noise suppression testing. The real result is that they've provided operation free of jittering/noise at times my other name brand receivers were showing weakness. Regardless of the swamping, noise and other factors, the only thing that moved my control surfaces were the sticks on my transmitter itself. The testing results show that factors have to be far beyond normal to cause a problems at the receiver.

Features like being able to double the amount of available channels by chaining two of them together also make this something that's more innovative than the rest. feel that these are the best receivers I have used to date.


  • Solid performance all around shown in the above test results
  • Made in Canada


  • The cardboard cases can get bruised, but there is some shrink wrap provided if that is your preference

Last edited by Angela H; Jan 19, 2009 at 06:13 PM..
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Jan 19, 2009, 07:06 PM
Wind blows
Laggard's Avatar
This is just an excellent review! I'd love to see more reviews like this of items not normally reviewed and tested. e.g. servos, escs, etc.
Jan 19, 2009, 08:57 PM
Registered User
BEC's Avatar

Great job! A serious test while being a fun read....that's not easy to do. I know, I've tried .

I have been more than impressed with Sombra receivers in the past. I have a couple of the older ones (Shadow 1, Shadow 3 - both synths) and they've been rock solid - though I've never challenged them to the degree that you have.

I, too, really like the "dial-a-channel" aspect - you can change the channel and be certain which one you have without ever turning on a transmitter. That seems to me to be the superior way - at least if one goes to a meet and wants to change channels because of other users. (Maybe the explosion of 2.4 GHz radios will make this concern moot in the future, but not yet).

Been there and done that on DSP transmitter recognition and buddy boxes, too. The more unlike the slave transmitter is from the master the less likely it will work. I find, for example, using a Multiplex Pico as the buddy box on my Evo works, but control response is slowed a little bit (this with Berg - I don't recall what I've tried along those lines with Sombra other than I did find some combos that worked OK). The folks that run Hitec and Futaba combos are clearly out of luck unless they can turn this feature off. Sombra now gives the option.

I think that the controls go quiet when a second transmitter on the same channel is stronger is really pretty darn good. If this potential interferer came out to the flight line turned on and got between you and your airplane the controls would get sluggish and then just hold as that took place, then the effect would go away as you got further away from the other certainly reduces the chances of a crash and is a far far cry from the airplane that's already on going crazy as soon as a second transmitter turns on. Great stuff.
Jan 19, 2009, 09:58 PM
War Eagle!
Spackles94's Avatar
Very nicely done, Arron! This was a hoot to read — and kudos to you on the unconventional testing methods!

I'm mostly a 2.4GHz sort of fella, but I still have some 72mHz stuff — this looks like a great option for areas where interference is the quip du jour.

And the price (especially for the six-channel one) is not too shabby, either.

Again, nicely done!
Jan 19, 2009, 11:22 PM
↓↘→ + (punch)
theKM's Avatar
Thanks guys. It makes the ridiculous cold wind during the range test worth it.

Laggard: there is certainly other things we need besides planes and motors.

BEC: the "turn off DSP" was a surprise to me, but it makes perfect sense. Interesting that for buddy-boxing that the only alternative to the Sombra Rx's is to go to cheapie Rx's that don't have DSP. And I'm looking forward to the dial-a-channel at this years SEFF!

Napo: sometimes unconventional is the only way
Jan 20, 2009, 07:11 AM
Registered User
poring's Avatar
Are they making 35mhz versions?
Jan 20, 2009, 11:40 AM
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theKM's Avatar
Originally Posted by poring
Are they making 35mhz versions?
Not as far as I know. Which is a bummer, 'cause I'd love to ship a couple to Sydney for Dad, but alas.
Jan 20, 2009, 11:47 AM
Registered User

Great review! Very informative / innovative

For all you licensed Amateur Radio enthusiasts out there, Sombra makes a version of this receiver on 50 Mhz. I have SIX of the synthesized 8 channel version and the range and rock solid performance is simply amazing. I have retired all my old JR ham receivers in my more expensive gliders and have moved to these receivers exclusively. I have never had a receiver which range checked beyond my ability to see my control surfaces move (Big 12' wingspan gliders!).

I did get 'shot down' at a large sailplane competition in Visalia CA. The culprit was standing about 50 yards away on the same channel. I didn't know it, and as I was launching the control surfaces failed to respond. It was as though power had been shut off to the receiver. I thought I had a switch/battery malfunction, but on the ground it was fully controllable when up close. As soon as I walked more than 20 yards away from the model, it quit working. Keep in mind, no glitching or wild servo movement, just like it lost power. I found the culprit only because I had a hand-held scanner which had a LOUD signal on my frequency when I shut my radio off! I then proceeded to run around the field and see what my signal strength did. As I closed in on my subject... it became obvious... and since he didn't have the frequency pin (thank goodness I DID!), he bought me some new parts to fix my plane! :-)

All that to say, Sombra makes a great product... but don't be fooled into complancency with regards to frequency control. As far as I know this is the only synthesized HAM BAND receiver on the market today. Covers BOTH 50 and 53 Mhz. Good stuff!

Jan 20, 2009, 02:27 PM
Registered User

100% confidence

I also use only HAM band Sombra Rx's. I have 100% confidence in their performance. The case could be a little better, but other than that no complaints.
Jan 20, 2009, 07:37 PM
Sippin' on Kool Aid
Excellent review!! i've been looking for a dual conversion 8 channel r/x for a while and this one seems to be it!
Jan 20, 2009, 07:41 PM
Suspended Account
Before I went to "all" 2.4, last year, I tried the SL-8 and it was clearly the best 72 mghz receiver I owned (and I had plenty of Berg 7's!).
Jan 20, 2009, 08:11 PM
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theKM's Avatar
Quality products with happy customers... how does that happen?
Jan 20, 2009, 08:23 PM
Suspended Account
Odd you frame it that way: I remember dealing with a fellow in Canada who was a real gentleman.

No "that will be extra," or "call back on the toll line," or "sorry about your credit card," just a fine guy with a fine product and no attitude except "the customer is always right."
Jan 22, 2009, 09:47 PM
Suspended Account
ededge2002's Avatar
ive been using sombra recievers for quite some time and have had no troubles with any of them. think im up to 5 total mix of 5 and 6ch ones.
Jan 22, 2009, 10:06 PM
Go Oregon Football!
MadCap231ex's Avatar
What a thorough review!

It is really great to see that 72Mhz is alive and well thanks to manufactures like Sombra Labs who can introduce greatly improved equipment without the need to change all your radio gear over. Best of all is the prices are very resonable for new equipment that is OEM compliant. Looks like my 9CAP is going to be around quite a while .

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