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Old Nov 02, 2012, 09:48 AM
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Depends. Are you a "radio engineer"? If not, then no, that won't satisfy shim.
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Old Nov 02, 2012, 09:50 AM
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Are you just being silly?
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Old Nov 02, 2012, 11:08 AM
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The second link has good information, I'm not sure what is in the first one - multiple posts came up. The thing is - you posted correct information but you didn't go out of your way to make an opinion about it. You didn't do what I was complaining about. The thing that bothers me is the statements like "clearly the Spektrum system is inferior because blah blah blah" and they put a bunch of stuff that is incorrect. That bugs me, but accurate information presented for the purpose of helping others understand will never bother me.
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Old Nov 02, 2012, 12:30 PM
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Originally Posted by jasmine2501 View Post
Please read these articles. I'm getting really tired of people thinking that spread spectrum means frequency hopping... Spektrum DSM2 is VERY misunderstood and unfair things are constantly said about it by people who don't understand DSS, so please, you owe it to yourself to understand so you can ignore/debunk those misleading statements.

http://en.wikipedia.org/wiki/Frequency_modulation - DSS makes zero sense if you don't understand FM basics
http://en.wikipedia.org/wiki/Direct-...pread_spectrum - this explains why, because of the PN ratio, you need higher frequency carrier waves to transmit a lot of data with DSS. Basically you need the ability to transmit a signal that is much faster than your actual data rate.
Thanks for posting these links jasmine - they are very interesting. I have to admit that until I read that information I was one of those people who thought he understood how DSM2 worked and therefore didn't think much of it... .

My new and improved understandng makes me think the vast majority of Spektrum issues in the early days were nothing to do with DSM2 itself. It seems far more likely that they were a combination of poor installations and a lack of understanding of the power requirements of a digital RX (especially given those early Spektrum RXs are known to have highish brownout voltages, now remedied in more recent receivers I understand). I will still never "go Spektrum" - I've invested in a FrSky DHT-U for my Mpx Evo and really like their system - but I will definitely get a DSM2/X module for BNF micros when the dual module FrSky TX comes out. Consider me partially converted!
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Old Nov 02, 2012, 12:31 PM
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Originally Posted by jasmine2501 View Post
Doesn't Futaba have new system called that? Is it strictly frequency hopping or is it a combo with DSS like FASST is?
Are you talking about FASSTest? AFAIK, that's just FASST with a back-channel for telemetry.

I don't think it would make much sense for Futaba to come out with something new that used FHSS, it's been fairly well established that DSSS+freq agility is the way to go (bluetooth doesn't work terribly great over distance, even with a power increase).
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Old Nov 02, 2012, 12:39 PM
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That was probably a reference to Futaba FHSS. From the Futaba site: "a less expensive way to enjoy 2.4GHz dependability".
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Old Nov 02, 2012, 12:57 PM
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My new and improved understandng makes me think the vast majority of Spektrum issues in the early days were nothing to do with DSM2 itself
Yes definitely, a lot of us had issues when we switched. For the most part, I just swapped out my RX with the Spek one and didn't really think about what I was doing. I had brown-outs, I had loss of signal problems, and over time I learned how to use the system properly - I lost a couple aircraft learning those lessons, and yeah I was pretty pissed about it, but not pissed enough to ignore the fact that I was the one who screwed up. I agree that Spek seems to be more sensitive to brown-outs than other brands, but I don't consider "this component requires electricity" to be a major design flaw.
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Old Nov 02, 2012, 01:00 PM
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That was probably a reference to Futaba FHSS. From the Futaba site: "a less expensive way to enjoy 2.4GHz dependability".
Yeah that... I have read what I could find about it and I can't see any fundamental difference between it and FASST. I wish they would explain that stuff for those of us who might understand it. I understand that it involves trade secrets, but the signal is out there and anyone with the right equipment could decode it and figure out how it works, so there's no reason for them not to tell us what it's doing.

At least they are using the acronym in the accepted way (FHSS has always meant "frequency hopping spread spectrum")
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Old Nov 02, 2012, 01:13 PM
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Yeah that... I have read what I could find about it and I can't see any fundamental difference between it and FASST. I wish they would explain that stuff for those of us who might understand it. I understand that it involves trade secrets, but the signal is out there and anyone with the right equipment could decode it and figure out how it works, so there's no reason for them not to tell us what it's doing.

At least they are using the acronym in the accepted way (FHSS has always meant "frequency hopping spread spectrum")
There's also S-FHSS, although I can't really determine what exactly the difference is between FHSS and S-FHSS, perhaps one of them is for park flyers.

I wouldn't put too much stock in the name FHSS meaning that the modulation is actually FHSS. After all Hitec called their technology "AFHSS" and it's definitely DSSS (as well as being "adaptive" only in the loosest sense of the word). If Futaba's FHSS is true FHSS, I'd be curious about its performance at significant range (that may be why it is relegated to the "economy" market).
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Old Nov 02, 2012, 01:44 PM
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Originally Posted by jasmine2501 View Post
Yes definitely, a lot of us had issues when we switched. For the most part, I just swapped out my RX with the Spek one and didn't really think about what I was doing. I had brown-outs, I had loss of signal problems, and over time I learned how to use the system properly
I'm curious as to what you've learned, specifically. I've been using Spektrum for a while..first as a module in my Futaba, and now a Dx8. I've only experienced one brown out in that time. It occurred when the plane was almost directly overhead. Luckily I got control back and landed safely. Never was able to pin point the problem.

Although I generally like the Spektrum, I've always had the feeling that the quality control just was not up to par with the likes of Futaba and the other. My Spektrum transmitter module died after only about a year of use (luckily not while I was flying a plane!). I got it replaced, but I was always a bit nervous about using it.
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Old Nov 02, 2012, 03:14 PM
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Originally Posted by jasmine2501 View Post
Yeah that... I have read what I could find about it and I can't see any fundamental difference between it and FASST. I wish they would explain that stuff for those of us who might understand it. I understand that it involves trade secrets, but the signal is out there and anyone with the right equipment could decode it and figure out how it works, so there's no reason for them not to tell us what it's doing.

At least they are using the acronym in the accepted way (FHSS has always meant "frequency hopping spread spectrum")
Futaba S-FHSS uses the TI CC2500 chipset (as per Hitec/FrSky/Graupner (I believe)/Corona/et al). It's configured to use 2-FSK modulation and it hops over 31 channels.

So no DSSS.

----

As a side note, does anyone know of any peer reviewed papers on long range links using 2.4GHz with different modulation techniques?

Si.
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Old Nov 02, 2012, 03:29 PM
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Futaba S-FHSS uses the TI CC2500 chipset (as per Hitec/FrSky/Graupner (I believe)/Corona/et al). It's configured to use 2-FSK modulation and it hops over 31 channels. So no DSSS.
Hmmm... that's why it's cheap! It's basically a PlayStation controller...

I'm not sure why they don't just make some low cost FASST receivers instead of confusing the market with three different flavors of Futaba.

Quote:
Originally Posted by Texas Instruments
The new CC2500 and CC1100 RF transceivers from Texas Instruments are the industry’s lowest system cost, multi-channel radios for low-power wireless applications. Operating in the 2.4 GHz (CC2500) and sub-1 GHz (CC1100) frequency bands, the devices include several useful digital features like full packet handling, FIFO buffers, clear channel assessment, wake-on-radio and more.
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Old Nov 02, 2012, 03:44 PM
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would seems in theory the best system would use 2 or 3 channels at the same time and leap frog them
ie one channel hops then the other with them hoping all the time
kind of a hybrid DSMX/FASST system with the hopping of FASST and the multichannel of DSMX
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Old Nov 02, 2012, 03:52 PM
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would seems in theory the best system would use 2 or 3 channels at the same time and leap frog them
ie one channel hops then the other with them hoping all the time
kind of a hybrid DSMX/FASST system with the hopping of FASST and the multichannel of DSMX
FASST uses two channels at the same time, while hopping, and spreading with DSS. Keep in mind that whenever you increase complexity, you decrease reliability (unless you do something to compensate for the increased complexity, and your compensation method represents another increase in complexity).

This might help... he shows the signals in frequency domain. (Note Hedy Lamarr in the preview slide)

2.4GHz Radio Presentation at Arvada Modelers Club Meeting June 2011 (40 min 13 sec)
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Old Nov 02, 2012, 03:58 PM
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Pretty hard to beat what we already have
The problems we see with our model aircraft systems is not rooted in interferrence problems.
The basic system Spektrum introduced works very well -as do the other brands commonly seen.
For the doubters - note that th little 64oorx (which use DSM2 - have an almost unbelievable succes profile -
This is because it is just about impossible to screw up the power system -.
One type battery - which always shuts the motor down with room for power to the rx.
If this system (DSM2)- were anything like some people claim - those planes would be falling from the sky like rain.
In the words of Pogo " we is met the enemy and it is us.".
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