New Lemon transmitter module, DIY & JR formats

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Dave McDDD
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Re: New Lemon transmitter module, DIY & JR formats

Post by Dave McDDD »

Mike_K wrote: 29 May 2021, 08:02 Hi Dave

You have virtually repeated my earlier experiment, except I used a 2.4GHz analogue FPV AV transmitter to select a single channel to block, not block both channels. Mine succeeded in moving the channel being blocked by the AV signal (but the other remained the same).
Mike, just to be clear, the Exceed/Flysky is only blocking one DSM2 channel (2.432 Ghz), not both. So this is exactly the same test you ran with an AV transmitter, except my DIY did not change the channel to avoid the conflict (2.432 Ghz). Is your module one of the beta test samples? If so, I've seen lots of posts on RCG indicating the beta units did indeed change to a different channel to avoid a conflict. But I've seen zero posts to date that a factory production unit like mine will ever select anything other than the two default DSM2 channels. According to Lemon the two default channels are selected by an algorithm that uses the unique ID of the transmitter module. I'm being told by Lemon that the transmitter modules scan the band to look for the quietest channels, and then select two of those for DSM2. The video proves that this is simply not true for this particular DIY module, and it's not true for any of the other five production version modules that I have. Each of the six modules happened to end up with different default DSM2 channels, but each module always chooses the same two default DSM2 channels, no matter what.
Mike_K wrote: 29 May 2021, 08:02I can't dispute what you're finding, but what does trouble me is that the FlySky should only be actually transmitting for a short period of each frame, typically a millisecond or two every 20mS or so and also the LemonRx will only be transmitting for 1.4mS every 22mS, so even if they happen to be on the same channels, the chances of the packets actually conflicting is still small. What protocol does the FlySky use, it isn't DSM2 is it?
I know the Exceed/FlySky FS-CT6A transmitter does not use DSM2, but I do not know what protocol it uses.

But to me the issue isn't that time sharing of the packets aren't able to cope with the channel conflict.
To me the real issue is that the production versions of the Lemon modules are ignoring the maximum possibility of RF interference by selecting one of it's two DSM2 channels on the exact same channel as the FlySky, even when the rest of the band was clear. In this case, the maximum possibility of channel interference was on 2.432 Ghz, and yet the DIY module selected 2.432 Ghz anyway as one of it's two DSM2 channels.
Mike_K wrote: 29 May 2021, 08:02I haven't got a FlySky transmitter to repeat this test, has anybody else got the gear to repeat it? Maybe there is something else going on that my test didn't replicate?
This sums up everything that I have been asking for from the beginning.

Thank you very much for your reply!
Built a Heathkit GD-19 in 1969. Been flying RC ever since!
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Mike_K
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Re: New Lemon transmitter module, DIY & JR formats

Post by Mike_K »

Hi Dave.

My LemonRx modules were ordered within hours of them going on the website, so they are production models, but must be early ones.

Mike
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Mike_K
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Re: New Lemon transmitter module, DIY & JR formats

Post by Mike_K »

Hi Dave

I've been trying to think what could be different between our tests. The first is that I was using a fairly powerful analogue transmitter. If/when the module scans at power up, there's no way it would miss it.

In contrast, if your Fly Sky works like the majority of protocols, it will only be transmitting for a couple of milliseconds every 20mS, so if the LemonRx module scans all channels, it probably isn't looking for 20mS on each channel and could easily miss the Fly Sky. But then it should work as the data packets shouldn't "collide" every frame. Is it worth repeating your test with a different brand DSM2 receiver to see if it's a receiver problem as well?

Mike
Dave McDDD
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Re: New Lemon transmitter module, DIY & JR formats

Post by Dave McDDD »

Mike, I've done this same experiment many times with Lemon 6 channel, Orange 6 channel, and Orange 7 channel DSM2 receivers. I no longer own any Spektrum DSM2 receivers, so I haven't been able to test them. I've even done it with both a Lemon and an Orange receiver at the same time. The results are always the same. The FlySky transmitter stops the DSM2 receiver(s) from establishing a control link with the DIY module until the FlySky transmitter is either turned off, or the transmitter is moved farther away from the receiver(s), or I wrap my hand around the FlySky antenna to reduce the output.

Again, the issue to me is that the DIY module is not avoiding an obvious potential channel conflict, regardless of time sharing aspect.
Built a Heathkit GD-19 in 1969. Been flying RC ever since!
Martin
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Re: New Lemon transmitter module, DIY & JR formats

Post by Martin »

I've written an Arduino sketch that allows an nRF24 module to transmit carrier wave (continuous unmodulated carrier) on a chosen frequency. I could also modify my RF scanner sketch to display the exact numerical frequencies of the two strongest signals it sees - rather than a spectrum display. I'll see if I can make something that listens to a Lemon module, and tries to jam either or both of its chosen frequencies with continuous carrier. It will require two nRF24s to block both at once. Might be a few days before I can do it.
Dave McDDD
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Re: New Lemon transmitter module, DIY & JR formats

Post by Dave McDDD »

Thank you Martin! That sounds like an interesting experiment.
Built a Heathkit GD-19 in 1969. Been flying RC ever since!
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stuart mackay
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Re: New Lemon transmitter module, DIY & JR formats

Post by stuart mackay »

Dave McDDD wrote: 29 May 2021, 22:05 Mike, I've done this same experiment many times with Lemon 6 channel, Orange 6 channel, and Orange 7 channel DSM2 receivers. I no longer own any Spektrum DSM2 receivers, so I haven't been able to test them. I've even done it with both a Lemon and an Orange receiver at the same time. The results are always the same. The FlySky transmitter stops the DSM2 receiver(s) from establishing a control link with the DIY module until the FlySky transmitter is either turned off, or the transmitter is moved farther away from the receiver(s), or I wrap my hand around the FlySky antenna to reduce the output.

Again, the issue to me is that the DIY module is not avoiding an obvious potential channel conflict, regardless of time sharing aspect.
Passed on the query to Lemon and they are making a post on RCGroups concerning this.
Hope this helps
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stuart mackay
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Re: New Lemon transmitter module, DIY & JR formats

Post by stuart mackay »

Here is a response from the designer at LemonRx for those concerned about their module on DSM2.


"Rebind the DSM2 receiver just before flying will ensure proper DSM2 channel is selected with proper brown-out indication for DSM2 receiver. Please note that DSMX receiver user should not worry about that as this is not affected with DSMX protocol."

If you continue to face problems, then please contact me in the first instance direct, and I will sort it out.

To be clear, DSMX users are not affected at all and will not see any of the symptoms mentioned above
Martin
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Re: New Lemon transmitter module, DIY & JR formats

Post by Martin »

Rebinding before each flight might be a work around, but it's not very convenient unless you equip the model receiver with a remote bind socket or button.

I do see the conflict. For the most rapid restoration of control after a transmitter reset (say accidentally switching the transmitter off and back on, or a loose/intermittent battery connection in the transmitter), the transmitter should use the same two frequencies it was using previously. But the module doesn't have a real time clock, so when it's powered up it doesn't know if it's been switched off for just half a second, or maybe six months!

I think the best compromise would be for the transmitter to preferentially reuse the same two frequencies it used previously, but first spend perhaps one second checking that those frequencies are currently only lightly used before beginning to transmit - and swapping to different, less heavily used frequencies otherwise.
Dave McDDD
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Re: New Lemon transmitter module, DIY & JR formats

Post by Dave McDDD »

Lemon has stated the new modules produced after May 29, 2021 will have an updated firmware. A procedure is in the works to update the older modules. Here is the post on RCG from Lemon
https://www.rcgroups.com/forums/showpos ... tcount=209

Martin, I would still like to see the results of blocking both DSM2 channels at the same time just to see what happens with the original firmware, and then with the new firmware.
Built a Heathkit GD-19 in 1969. Been flying RC ever since!
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