[TimCo]

A rather poor video, 

2.4GHz FHSS Radio-control: Fly Sky interferes with RadioLink system

  but an attempt to illustrate the susceptibility of the RadioLink T4EU Tx and R7EH Rx to interference from a Fly Sky FS-T4B / FS-R6B system by way of the following steps:
1. Servos on the RadioLink system glitching when both RadioLink and Fly Sky Transmitters are operating.
2. Fly Sky Tx turned off. Servos fall silent.
3. RadioLink joysticks operated: servos move as expected.
4. Fly Sky Tx turned on again. RadioLink joysticks operated: servos move in jerks.

In the video, the transmitters are very close. I have retested outdoors. The same thing happens when the two transmitters are 1m apart and the receiver 30m away. With an ESC the interference is dramatic: the motor speed fluctuates wildly, then the motor stops and must be restarted by zeroing the stick.

The Fly Sky system has performed reliably for me for the last six months, as well as throughout this test. The RadioLink system, with two Rx's which both perform (or fail) in the same way, is a recent purchase intended to allow two of my 2.4GHz models to operate at the same time. Clearly, it fails in this. I write this as a warning to other owners of these low-price  (or other) systems and to ask whether anyone else has seen the same problem.

[FrankS]

Interesting, I must admit I've never experienced anything similar when using Spektrum DSM2, FrSky (non-telemetry) or Multiplex M Link (other users were mainly Futaba, Hitec, FrSky and Spectrum DSM2/DSMX).

Just a thought could one Tx be affecting the other Tx, i.e it's not actually radio interference but the FlySky tx is radiating electromagnetic interference which disrupts the Radiolink Tx operation (or Radiolink Tx electronics are susceptible to external interference), what happens if you move the transmitters say 5m apart.

[TimCo]

Thanks for the suggestion. With a quick indoor test and only 7m to play with, the worst possible performance comes when the RadioLink Tx and model are 7m apart, and the Fly Sky is half-way between them: it does not get any worse if the Fly Sky is moved towards the model from there. With the Tx's 7m apart and the model in-between, there can be long periods without a glitch, although with the Fly Sky transmitting, the RadioLink set might take 30s to bind. In terms of glitching frequency, it does not seem to matter in what order the three devices have been powered-up. Since there may still be hope of a solution from spacing the pilots, I shall try again outdoors in daylight!

[TimCo]

Tested again today, outdoors. Tried spacing the two transmitters approx. 5m and 10m. Walked around with the model up to 50m away. Servos glitched all the time unless the model was substantially closer to its RadioLink Tx than to the Fly Sky. Again, the worst case seemed to be when the Fly Sky Tx was in the middle, between the RadioLink Tx and Rx. Apparently unusable!

[Yoyo]

Tested again today, outdoors.

As the doctor said to the man who said touching his toes made his back hurt, 'don't do that then'...

Seriously, do you have to have those txs operating like that? There's obviously an interference issue between them that doesn't seem to bother anything else.

Flysky didn't do well for interference rejection in the rcmodelreviews tests, FRSky did much better in that price bracket. I don't know much about radio link.

The whole frequency hopping and spread spectrum strategy (FHSS) used by the various 2.4 manufacturers varies from really simplistic to very sophisticated.

Can you either keep them away from each other, or replace the RF stage of one with a different type of module?

Have you tried rebinding one or both to see if it changes anything?

[TimCo]

Perhaps I should have explained better. The outdoor test was to rule out the suggested possibility that the Fly Sky Tx was interfering with the proper operation of the RadioLink Tx (rather than Rx). The transmitters were spaced apart at different spacings quite likely to be seen between modellers at flying field or pond-side and the RadioLink system continued to glitch. I have had 6 months reliable operation from the Fly Sky set: I probably should have purchased a second Fly Sky Tx to allow a guest to control a second model (applicable to boats, at least!), but chose the similarly cheap RadioLink only in order to have two identifiably different Tx's!

Also outdoors, I did a range-check, albeit in a residential area, with only one R/C system running at a time. With the transmitter in my back garden, I walked out of the driveway with a small model boat, with ESC/motor running at "idle", and continued along the road until the motor stopped and the ESC bleeped to indicate loss of signal. With the Fly Sky, this was achieved without glitch or spurious motor response. The RadioLink, installed identically, gave a similar ultimate range, but for the last 20% of this, the servos glitched wildly and the motor revved and stopped, indicating susceptibility to some other source of interference, perhaps WiFi.

Further, indoors, with RadioLink glitching evident on start up of the Fly Sky, pressing the Fly Sky's "range check" button, to reduce RF power, made no difference.

I purchased two RadioLink Rx's: they both perform the same. Rebinding does not seem to help.

[Yoyo]

Perhaps I should have explained better. The outdoor test was to rule out the suggested possibility that the Fly Sky Tx was interfering with the proper operation of the RadioLink Tx (rather than Rx).

My fault - I didn't go back and reread the thread before posting... 

It does sound like the problems are actually all at the Radiolink end, with it being very susceptible to interference. Have you got any other potential sources of interference, other transmitters, videosenders etc?

I'd be tempted to bin it or at least FRSky it. Even with boats you don't want radio gear you can't trust.

 

[TimCo]

Thanks, Yoyo
I complained to the UK vendors of RadioLink on the day of receipt (13 March 2012), ending with the query, "Could you look into interference between Fly Sky and RadioLink gear? Do you think mine might have a fault, or is there a mistake in the design?", and have copied them with my subsequent tests, as above.

Guess what? Today they have replied with the suggestion that I return the Tx and two Rx's to them so that they can have them tested because the Tx might be low on output: if deemed not faulty, I have to pay 30% of the original purchase price for the testing, plus postage!

Outrageous! Their only hope should be that my Tx IS faulty. If it isn't, we should consider that the RadioLink design of FHSS system is not fit for purpose.

[capt2724]

Hi guys,
With regard to the Radio link transmitter problem, it might be the other set Tx that is causing the problem. i have 2 Radio link Tx and niether of them have had any interference issues from close proximity to JR, Futaba, Spektrum or Hitec. I have flown with mine alongside clubmates using these other makes all at the same time. No problems were encountered.

[TimCo]

With all the above considered, I have done three further tests today:

1. A comparative range-check, as before but in a flat, rural location. No houses for at least half a mile. One RC system at a time. With the transmitter on the ground, and walking away with the model. Tx and Rx antennas vertical. The Fly Sky system gave 300m before the ESC bleeped "no signal", and the servos did not glitch. The RadioLink achieved around 350m, but the last 50 were accompanied by glitching and erratic ESC.

2. Range checks as above, but when the Fly Sky system was tested, the RadioLink Tx was switched on, and carried along in my other hand, i.e. 0.5m from the model, and vice versa for the RadioLink system. Result for the Fly Sky was exactly the same: at 300m, no glitches, ESC started to bleep. For the RadioLink, as expected, the servos glitched from zero distance and worsened as  both model and Fly Sky tx were moved away. The ESC became erratic at 10m and stopped the motor, and the test abandoned at 50m.

3. Back indoors, a bluetooth-equipped phone was set to "search for new devices", near to the model, with the Tx at a 5m distance. With the Fly Sky system it was impossible to disturb servos or ESC this way, even with the phone touching the Rx antenna. With the RadioLink, the servos and ESC were affected as per my original video, when the phone was searching, but the phone had to be within 300mm of the Rx.

I would also like to reiterate that the troublesome system comprises RadioLink T4EU Tx and R7EH Rx. I believe the majority of sets sold are with a different, 6-channel, Rx.

[JohnP]

I'm puzzled that you are getting any glitching (35 MHz-style) on a 2.4GHz system.   

To me, one of the major points of any(?) 2.4GHz system is that it used packets of data that are (or should be) checked for corruption and addressed specifically to your rx.  Any corrupted data or data addressed to any other rx should be ignored.  So there should be no reason for any glitching.  Compare this to 35MHz where the receiver will attempt to interpret any signal it receives (whether from your tx,  somebody else's tx or just interference from god-knows-where) as a set of commands to pass to the servos.  It's almost as if the Radiolink is using 35MHz-style analogue technology but on a higher frequency!   I know that's not what they claim, but...

[dickw]

I'm puzzled that you are getting any glitching (35 MHz-style) on a 2.4GHz system...........

At extreme range or in the presence of strong interference any 2.4GHz system can lose and regain the signal quite rapidly. What is does at that point depends on it's failsafe setup.
Each time it loses and regains signal the servos could stop and then play "catch-up", or they could move to a predetermined failsafe position and then play "catch-up", or in a poorly designed/specified  system the servos might be influenced by signals directly induced in the Rx output stages by intereference.
Any of these scenarios could look like "glitching" in the old 35MHz sense of the word.

Dick

[GlowFly]

There's really little reason not to use error detection on 2.4GHz since there's so much excess data carrying capacity and a correctly designed spread spectrum design should preclude such interference from being decoded in any case. It actually sounds as if Tx RF power is entering the Rx directly and interfering with the digital circuitry. I've seen this sort of thing when unused CPU inputs are tied weakly to a supply rail or left floating.

I agree there should be no 27/35MHz style glitching present on 2.4GHz in any case.

Steve

[TimCo]

Thanks for these comments. I found a person today who had a Spektrum Dx6. This did not cause my RadioLink set to glitch, even when very close to the Rx. I realize now I should have written down the exact model, Dx6 or Dx6i; if anyone needs to know, I can find out.

[TimCo]

I give up! I have returned the RadioLink Tx and two Rx's to the vendor, with the following suggestions, inferred from the above tests, which I hope they will find helpful, rather than irritating:

" (a) The transmitter is low on RF output. This is possible even though the range is as good, or better than, that of the Fly Sky set. If, however, one could, say, double the Tx output, would this not merely make an incremental change to the relative distances at which servos would start to glitch, etc?

(b) Both receivers are faulty. This would be very unlucky, and, because of the range check result, unlikely.

(c) The receiver design is at fault. From what I have read, spurious servo movement and ESC operation, like was often seen in 27MHz systems, should not be possible with 2.4GHz, even when there is interference.

(d) The RadioLink FHSS system is not good enough.

(e) The Fly Sky “Automatic Frequency Hopping Digital System” (AFHDS) somehow “confounds” the RadioLink FHSS, such that it is the only RC brand that cannot be operated nearby. This seems unlikely, in the light of the RadioLink’s response to interference from other sources.

I am disappointed by all this because there are some features of the RadioLink that I prefer over those on the Fly Sky: the joysticks, lanyard-attachment and receiver antenna (easier to install)......"

After sending the stuff back, I thought of another possibility:

(f) The transmitter has a fault, such that it does not correctly identify the free channels on which it should choose to transmit, i.e. like (d), above, but owing to a manufacturing, rather than design, fault.