Espritmodel.com Telemetry Radio
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Old Dec 27, 2013, 12:39 PM
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Adekamer's Avatar
Russia, Moscow, g. Moskva
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New Product
Rlink LRS

Hi, Merry Christmas!
new LRS http://www.himodel.com/FPV_Telemetry...HF_System.html
super high sensitivity as -115dBm
RSSI output(analog buffered) in separated channel in the Rx side
twin antenn (may be diversity)
look awesome, who know this product ?
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Old Dec 27, 2013, 01:01 PM
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It's got a nice list of features. The only thing of concern is the wide selectable frequency
range. It means the Rx does not have a narrow band pass filter so it may be
possible to swamp the front end if there's high power external Rf interference on a nearby
frequency band to whatever you're using. DTV signals at 470+Mhz for instance
while you're flying on 433. I've had some issues with this with other UHF systems
in the past.
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Old Dec 27, 2013, 05:29 PM
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Daemon - you think the front end is wide open? Need to make sure I understand you properly - is the suggestion that the whole 100Mhz is "open"(?), or that the "open" bandwidth at any time is some smaller bandwidth setting within this overall 100Mhz operational bandwidth(?).

I can't see any on-line spec's that define what the open bandwidth at any point in time is, but what I do know is this: that - 115dBm across a 100Mhz bandwidth assumes a signal to noise ratio that is ... well, just not plausible (and I guess you'd be aware of this as well). Hell, we battle to achieve much better than around -90dBm with the +/-5Mhz bandwidth the typical FPV video receiver uses - so, just how are they achieving -115dBm?

What are the practical options?

- the real "open" bandwidth is a smaller bandwidth within the overall 100Mhz?

- the open bandwidth [at any point in time] is the bandwidth of each hop - implying that not only is each Rx/Tx pair matched through a unique ID (a given product spec), but that they are also synchronized (which is not a given spec)?

Can you see any other options been possible - any other configurations?

In both the above cases a receiver sensitivity of -115dBm would be plausible with an open bandwidth at any one time of round 50Khz - and if looked at more specifically as an rf signal carrying digital data (irrespective of the encoding/modulation technique) we also don't see much in the spec's about this either, but there's going to be an upper limit here as well, and some info on this would certainly lend plausibility to the performance claim been made for this product.

For those who are not aware: there is a max upper level sensitivity for any given bandwidth, beyond which it is impossible for any receiver to function. Max possible sensitivity for any bandwidth can be calculated so long as (as is the case with all math calc's) you have the required input figures to work with, which in the case of max sensitivity/bandwidth calc's requires having figures for things like Noise Factor, Boltzmanns Constant, min SNR .... and a couple other bits 'n pieces of info.

The figures I have given above are theoreticaly plausible and off the top of my head I believe to be real-world realizable as well. If someone wants to go ahead and undertake exact calcs to confirm or refute what I have stated please feel free to do so - no objection at all.

The question, as so often is the case with rf hardware out of the Far East, is really: are the spec's been claimed by the product plausible, and if so for just what setup conditions or circumstances are they realistic and/or real-world realizable?

Personally, from what I can see, I believe the manufacturer needs to provide a bit more info before this unusually good, but not impossible -115dBm figure can be accepted as been an accurate real-world figure.

Its like the mileage/gallon figure car manufacturers give: possible in theory, but effectively impossible to realize in real-world conditions, and thus misleading.


PS - a few days back someone posted up a link on the FPV forum, to an FPV usable rf hardware product that had a very similar set of spec's, if not indeed the same product - or quite possibly another product but making use of the same core IC set(?).
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Old Dec 27, 2013, 09:59 PM
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I can't really speak to the sensitivity claims. That's probably the spec of the receiver
module. Around here the noise floor is much higher than that so couldn't make
use of the anything in the -115 to 95dB range anyway.

Here's what I was getting at. There are some UHF systems that are designed
to work only between 433-434Mhz, and they put a narrow bandwidth SAW filter
on the front end. Some other UHF systems do not have a SAW filter, and
they rely on the Rf module to handle filtering and tuning across a potentially wide range
of frequencies. The latter is great if you need to tune for other legal
bands in different countries and such, or move away from narrow band low power
interference stepping directly on your channels. But, in my experience they can
get thrashed pretty easily by powerful signals that are near the frequency band
you're using, but not directly overlapping it (not just noise floor increase at the
tuned frequency). Wouldn't surprise me if the specs say this sort of thing
shouldn't be happening, but my ground range tests, and flight tests show otherwise.
Others have experienced the same thing.

ian
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Old Dec 28, 2013, 03:37 AM
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Interested in this product too, but it's very new, high risk to try
Subscribled.
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Old Dec 28, 2013, 01:35 PM
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Okay – some additional info on this product, and as was suspected – the devil is indeed in the detail, although there are some interesting features.

To make use of the full 16 channel transmit capacity of the transmitter, you need to invest in 2 receivers as each receiver is limited to a max of 8 channels!

PPM data from your Futaba, Spectrum, Hitech or whatever brand name radio you use, is input into the RLink long range module via 2 separate 4 pin Molex connectors as 2 separate PPM data streams – each connector good for 8channels (max) .

The RLink module multiplex’s the 2 PPM streams into a single output stream.

The channel sequence can be set by the end-user – useful as different folk will be using different brand name radios, which as everyone knows can use different channels for different purposes (e.g. Futaba uses the first 4 channels as follows, 1(Aile), 2(Elev), 3(Throttle), 4(Rudd), 5(Gear), 6(Aux1) but JR uses them as follows 1(Throttle), 2(Aile), 3(Elev), 4(Rudd), 5(Gear), 6(Aux1) )

Things could be quite interesting subject of course to what access the designer/manufacturer gives end-users to the firmware. Great that end-users can define what channels are used in what sequence for what, but what about settings like allocating priorities and repeat rates etc etc …….

No software has to be loaded into your smartphone/PC/tablet or whatever you want to use, and you can be running Windows/Linux/Android whatever, apparently all are suitable OS’s for use with the RLink long range system just connect the hardware to whatever you are using with the included micro-USB cable. Simple(?) – probably, but it also suggests limitations to what end-users have/ do not have control over.

The real interesting point is that (thru firmware settings accessible via a micro-USB connector) the “open” band-width within the overall 410Mhz – 510Mhz operational bandwidth can also be end-user defined - both in terms of where it is placed between the 410Mhz lower frequency, and the upper 510Mhz frequency limit, as well as the “width” that is used so long as it is at least 2Mhz wide – but where you locate this 2Mhz plus wide open band-width in the overall 410Mhz - 510Mhz is entirely up to you and/or local rules & regs(!)

Max bandwidth you can use appears to be the whole 100Mhz between 410Mhz - 510Mhz!

What also isn’t 100% clear from the on-line PDF doc is if this min 2Mhz band is per receiver (i.e. for a max of 8 channels of PPM data), or is the tightest bandwidth that all 16channels of PPM data can be squeezed into?

My suspicion is that all 16channels can be carried in this min 2Mhz band-width – well, a PPM data stream carrying 16 channels at more than sufficient bit rate for FPV applications, can quite easily be carried in a 2Mhz bandwidth - but, and there actually 2 "buts" to this:

- firstly, the issue of the -115dBm receiver sensitivity – I think we can be pretty dead cert that this exceptional figure is only going to be valid if the bandwidth is 2Mhz … the devil in the detail again …. and that it fast deteriorates as you increase bandwidth – which leads onto the 2nd little devil in the detail .....

- you need to increase bandwidth to maintain a real-world usable link security as at 2Mhz in many situations, you will have cut your resistance to interference to its absolute min and in many cases will, or could find yourself trying to maintain your RF link right on the limit ….. another expression comes to mind, "no such thing as a free lunch in rf engineering”.



So, now that the -115dBm sensitivity figure has been qualified it can be put into context: as impressive as it may be, just how useable in real-world FPV flying circumstances it turns out to be, is another issue altogether - you will need to decide which is more important, or which you value more:

Receiver sensitivity or Link security (& resistance to interference)?

The reality is that there will be FPV flying environments & circumstances in which Sensitivity is going to take priority, and there will be FPV flying environments & circumstances in which Link security is going to take priority
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Old Dec 28, 2013, 02:15 PM
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2.4GHz RC receivers are quite common listed at -110 dB, but... as you emphasized, at 1MHz
So -115dB at 2Mhz is normal, outstanding will be the future LR receiver of Frsky, expected to have -120dB.
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Old Dec 28, 2013, 04:35 PM
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Quote:
Originally Posted by renatoa View Post
2.4GHz RC receivers are quite common listed at -110 dB, but... as you emphasized, at 1MHz
So -115dB at 2Mhz is normal, outstanding will be the future LR receiver of Frsky, expected to have -120dB.

Aaaah, yes Renatoa - I hear you but this -120dB means nothing in the absence of the signal bandwidth - have you any idea what that will be?

As well, do not forget the other half of the equation - which is often overlooked, - and it is this:

Receiver sensitivity - even with a small figure for bandwidth - still means little & tells an engineer little - no matter how high the receiver sensitivity figure may be for the bandwidth it is designed to work with, unless the SNR part of the equation is also included:

You could have -120dB sensitivity and 1Khz bandwidth, but if the receiver front-end IF filters and/or mixer stages have poor SNR figures, or cannot cope with the SNR the -120dB/1Khz signal is presented with, no matter how sensitive the receiver may be it will not be able to demodulate the received signal unless the SNR requirement is satisfied - and a un-demodulated received signal is as good as a chocolate teapot!

So in addition to the Frsky bandwidth figure, just what SNR is required for demodulation to take place?
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Old Dec 31, 2013, 04:48 AM
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The only we know so far is...

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Old Dec 31, 2013, 02:13 PM
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Renatoa

You have a 9912A! – nice – very nice - congratulations, sir.

Do you have (or have access to) an Rlink 16-Channel Long Range UHF System (Tx & Rx pair), and, or a pre-launch example of the FrSky Taranis LR12 receiiver?

It would be great if you could setup your 9912 for some basic SNR figures(?) - okay, results ain't going to be to FCC/CFR, but hey, so what - they'll be good enough to give an indication of performance (I would happily do this myself at home - but I don't have an RLink or a Taranis receiver). My guess is [if you have a 9912] you're not going to need any "how to" advice from me (or anyone else), but if you want some input, quite happy to share with you how I'd go about using a FieldFox to get some usable SNR figures for a receiver.

On the subject of FrSky - the more I read about their products the more I like the [open source] philosophy they have adopted - huge potential!

Back to FPV RF hardware specs and performance: the best performance info we get is the info members post up and share about their own personal "user-experiences". But sadly, these reports (from a performance perspective, at least) are good for their experience only, and in a few cases, good for comparison with any particular Tx or Rx hardware they may have compared alongside the gear they were reporting back on primarily - so long as the comparative notes are based on comparisons between different hardware types/configurations conducted on the same day same at the same flying location.

Still, almost always missing – through no fault of their own – are 2 very important pieces of info:


- background RF noise level around the ground station/base station while they were flying

- SNR (derivable in no small part from the first bit of info)

This 2nd piece of info can quite easily be supplied by manufacturers – especially those who undertake serial type production (does anyone know why manufacturers don't or are reluctant to supply min usable SNR figures and provide background RF noise levels when undertaking their own tests?). Figures don't have to be to FCC/CFR standards (although I guess some standard would need to be agreed on) e.g. basic noise levels (dB) along with the centre freq & bandwidth of the associated noise could be a starting point(?).

With these figures FPV flyers would have some basic comparative side-by-side-performance data for different transmitter/receiver combinations - especially receiver performance - but till then................... ??


Note
Folk who are interested in making these sorts of comparisons can gleen useful info from FCC reports in cases where FPV/RF hardware has received FCC approval.
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Old Dec 31, 2013, 08:03 PM
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Is RLink the same is RangeLink?
Why are the sames very much the same?
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Old Dec 31, 2013, 09:01 PM
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They are not the same. Just speculating but I wouldn't be surprised if they use the same Rf modules
though (different version of the same module is also used by original Chainlink, and Dragonlink).
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Old Jan 01, 2014, 03:57 AM
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Quote:
Originally Posted by CarbonWings View Post
Renatoa

You have a 9912A! nice very nice - congratulations, sir.
...
On the subject of FrSky - the more I read about their products the more I like the [open source] philosophy they have adopted - huge potential!

...
Not my plot, lol, the source of image can be found easy, if you quote my post. However, I have access to such tools if needed.

"On the subject of FrSky" ... I think this is a thing of the past, OpenTx is just the swan song, I am afraid they will close in the future, as every respected big brand they believe have become ...
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Old Jan 01, 2014, 04:59 AM
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Originally Posted by renatoa View Post
Not my plot, lol, the source of image can be found easy, if you quote my post. However, I have access to such tools if needed.

"On the subject of FrSky" ... I think this is a thing of the past, OpenTx is just the swan song, I am afraid they will close in the future, as every respected big brand they believe have become ...

Yes - I think you may have a point there.
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Old Jan 04, 2014, 07:49 AM
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anybody tested this yet, seriously considering it, hopefully it will have at least same range and performance as ezuhf

thanks
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