Espritmodel.com Telemetry Radio
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Old Jan 21, 2009, 07:16 AM
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EzUHF, the full duplex long range link with FHSS and diversity

***PLEASE USE THE BELOW NOTED TOPIC FOR EZUHF DISCUSSION***

http://www.rcgroups.com/forums/showthread.php?t=1216176

Alright, I guess I couldn't keep this under wraps for too long, as I have had quite a few people asking for pricing already. So I'll disclose a little more info to satisfy all of you tech savvy FPV-ers.

The EzUHF is the EzOSD's little brother (or sister) and basically is a selfcontained full duplex long range link which can be selected to operate on a variety of frequency bands (315MHz, 433MHz, 868MHz, 915MHz) with RF output power ranging from a mere 10mW to 500mW.

It consists of two transceivers of which the one on the plane uses a diversity antenna configuration and hence has about 8 to 10dB gain in sensitivity. The ground based transceiver connects directly to your transmitter's trainer port and hence is transparant to your RC transmitter, it doesn't know it is not talking to a different RF output stage.

EzUHF transceiver, 2nd prototype



The Rx transceiver will be a 8-channel design which utilizes the i2c bus to talk to the EzOSD and give you meaningfull info (such as received signal status, good/bad packet count etc.) and will be the same size as a conventional RC receiver. The UHF link features a very robust FHSS implementation and has a binding relationship with the Rx/Tx transceiver (hence can't receive packets from a similar Tx close by). Above I've pictured my 2nd prototype which is still a bit large so I can poke around with the scope probe without too much trouble. This very same Rx transceiver is featured in the below video of a long range flight with one of my Ez testbeds.

On thing to note is that during this entire flight the Tx transceiver output power was fixed at *50mW* and a normal whip antenna was used on the Tx. This is far lower RF output power than a normal RC transmitter puts out, and a factor of 10 lower than what other long range solutions require. One other thing to note is that with the EzTelemetry feature there's endless possibilities for plotting RSSI and all sorts of other info onto a live Google Earth map as all of this data is transmitted from the EzOSD to the ground station (and tracking antenna).

Long range flight with the Ez

http://www.vimeo.com/2906525

Pricing and availabilty is not yet known, as I know that question is eventually going to pop up. We're investigating the requirements for HAM license free operation in a variety of countries at this moment. As although the FHSS guarantees it doesn't pollute a frequency already in use for too long, we'd rather come out with a solution anybody can use rather than something that's restricted to HAM licensed users only.

Cheers,

Sander.
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Old Jan 21, 2009, 08:25 AM
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boopidoo's Avatar
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Cool, these Ez-stuff may very well be what I'm looking for. I'm looking forward to more information on price etc.

Great work!
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Old Jan 21, 2009, 08:41 AM
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Interesting. I didn't watch the video yet, but will do that tonight.

Can you say anything on range? The title says long range, but you don't specify how long.
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Old Jan 21, 2009, 08:59 AM
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Sander,

how do you handle the Tx duty cycle restrictions (10%) on 868 Mhz ?

Greets, Erwin
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Old Jan 21, 2009, 09:01 AM
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Well, range depends on RF output power mostly, as mentioned this is a work in progress still so I have yet to explore the outer limits (I don't fancy losing a prototype several kilometers out) but at 50mW (that's 5-0, not 5-0-0) RF output power I managed to go out well over 3 kilometers at an altitude of just 100-meters. If I go up higher (>250-meter) 5km is certainly possible. With more RF output power comes longer range, hence at 500mW I expect to be able to go out well over 10km.

The Rx/Tx will likely feature an 'OH SH*T' mode that'll tell the Tx to boost the output power if the Rx detects a large packet loss, however details of what power we'll switch to are yet to be determined, but that'll probably be 500mW.

Cheers,

Sander.
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Old Jan 21, 2009, 09:03 AM
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Erwin,

Quote:
how do you handle the Tx duty cycle restrictions (10%) on 868 Mhz ?
The FHSS (frequency hopping, spread spectrum) takes care of that. Basically you divide the freqency band in x chunks of xxxkHz and then you hop to the next frequency every x ms (incremental, or random), so the total duty cycle on each frequency is a mere few %.

Cheers,

Sander.
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Old Jan 21, 2009, 09:27 AM
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Sander,

ah, ok, thanks. Very interesting gadget you've developed here ...

With which frequency do you the testflights currently ? Have you tried also 868 Mhz already ?

Erwin
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Old Jan 21, 2009, 09:50 AM
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Arffff , can't wait ,


need Beta tester in France , I'm your man

Rgds
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Old Jan 21, 2009, 01:16 PM
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Quote:
Originally Posted by _helitron_
Sander,

ah, ok, thanks. Very interesting gadget you've developed here ...

With which frequency do you the testflights currently ? Have you tried also 868 Mhz already ?

Erwin
Hi Erwin,
We haven't tried the 868MHz version yet, testing so far has been down around 433MHz. Its only a few 'L's and 'C's to change to shift band though, the silicon fully supports it. Just need a few lines of code changed.

The 10% rule is an interesting one because the 868MHz band is not really wide enough to support FHSS over a large number of bins.
There are several tricks that can be played though, the FHSS algorithm in the system can support many missed bins before loosing sync, so the system doesn't have to transmit every packet when controls are not changing (the AeroLink 1 did this, without the FHSS).
It could also transmit truncated packets when there is no activity, keeping the total Tx time down.

-- Anthony
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Old Jan 21, 2009, 03:05 PM
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Hi Anthony,

glad to hear from you again ! Perhaps you remember, I was also interested in the AeroLink 1 system some times ago . But unfortunately I've had bad luck with my Aerocomm modems from Mouser during the tests on the bench (without your AeroLink 1 of course) and got never a realiable connection between them, Hartwig tried the thingies also in Germany with the same bad result. I think there is a bug in the firmware revision of my modems.

In the meantime I own a 433 Mhz system from Thomas Scherrer but didn't have the chance to try it out really due to weather and other circumstances. But the first short tests end of last year were successful so far.

The big plus of your new system in my opinion is the combination of R/C and telemetry and additionally the connectivity to the EZOSD and the antenna tracker of course. A real powerful package. The frequency is not really much important in my case because last year I've got the HAM licence, so I've now a bit more possibilities regarding frequency and output power. That means 433 Mhz would be also ok for me.

As the other guys, now I'm also very curious already about the costs of this new system of course .

Cheers, Erwin

Quote:
Originally Posted by AnthonyRC
Hi Erwin,
We haven't tried the 868MHz version yet, testing so far has been down around 433MHz. Its only a few 'L's and 'C's to change to shift band though, the silicon fully supports it. Just need a few lines of code changed.

The 10% rule is an interesting one because the 868MHz band is not really wide enough to support FHSS over a large number of bins.
There are several tricks that can be played though, the FHSS algorithm in the system can support many missed bins before loosing sync, so the system doesn't have to transmit every packet when controls are not changing (the AeroLink 1 did this, without the FHSS).
It could also transmit truncated packets when there is no activity, keeping the total Tx time down.

-- Anthony
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Old Jan 21, 2009, 03:12 PM
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Looks like a very interesting device. Does it support seperate fialsafe programming for each RC channel ??

JettPilot
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Old Jan 21, 2009, 03:26 PM
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How many bits of resolution per channel? This is a concern to me,
because on Thomas' system he only sends 8 bits per channel which
means only 256 steps, which makes camera panning noticeably jumpy
and can make it tough to trim the elevator on a glider.

Do you plan to have a pass through on the trainer port
so people can still use head trackers, and in my case buddy boxes?

ian
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Old Jan 21, 2009, 03:30 PM
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Jett,

Quote:
Does it support seperate fialsafe programming for each RC channel ??
No, it is based on PPM encoding (as PCM differs per brand) and most RC transmitters don't have any failsafe options for PPM. However we do have a global failsafe. Basically a press of the button on the EzUHF Tx stores current settings to the EzUHF Rx as the failsafe position. So if you trim your plane out in flight, and press the button, that'll be your failsafe settings.

Cheers,

Sander.
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Old Jan 21, 2009, 03:35 PM
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Ian,

Quote:
How many bits of resolution per channel?
We use 8-bits as well, indeed giving you 256 positions per channel. I've not noticed any jumpyness in any way, shape or form, esp. since most servos have about 60-degree of travel anyway, which gives you a granularity of 60/256 = 0.23 degrees.

I use both the EzUHF and a Futaba PCM system, with 1024 steps per channel, but can't notice any difference (other than the fact that cheaper servos now *do* find their center position which they could often not with PCM's 1024 steps).

Quote:
Do you plan to have a pass through on the trainer port
so people can still use head trackers, and in my case buddy boxes?
Yes, else it'll be hard to use a head tracker indeed.

Cheers,

Sander.
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Old Jan 21, 2009, 03:40 PM
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Hey Erwin,
Good to hear from you too. Yes, the AeroComm modems were a frustrating experience. They initially showed a lot of potential, no worries about certification in the EU, and allowed hours of incident-free long-range flight.
But... every once in a while something would happen which made me doubt the system. After many frustrating hours, and too many calls to tech-support, we had to abandon them. The fact that there was someone else's buggy firmware between our code and the RF link was a real blocker :-)

The telemetry link has been quite useful in testing the new system. A live 3d plot in google earth of the signal strength at each of the antennas is quite reassuring to see :-), and for post-flight analysis of antenna positioning, antenna design, etc. its a real help!.
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