FHSS versus DSSS, which is best?

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Re: FHSS versus DSSS, which is best?

Postby skyguy04 » Thu Jun 03, 2010 12:05 am

I'm not as well versed in the technical side of radios as you guys are, but it is interesting that Carl Orr uses primarily 9+ channel JR/Spektrum receivers that have 4 satellite's. Of course the numbers are going to be way in favor of JR/Spektrum if your testing 4 (5) receivers vs. 1-2? I have had a personal experience with this issue. I put a 6 channel (AR6200 I think) in my 1/4 cap 232, which had 1 satellite. It kept getting hit at the field in flight, when i was the only plane in the air. A buddy had an AR9000 receiver with 2 satellites that he wanted to get rid of, so i swapped mine out with his. Sure enough, it increased the range exponentially and i didn't have any hits. So i paid the man and that is what i fly in my Cap today. I moved the 6 channel to a foamy and it works just fine.

So does this mean that if you're going to stick with DSSS, you better fly with a minimum of 2 satellites in any plane of substantial size? So basically you've got to spend $203 for a reliable giant scale application, minimum.
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Re: FHSS versus DSSS, which is best?

Postby RCModelReviews » Thu Jun 03, 2010 12:31 am

The 9-channel receivers seem a little more sensitive than the others and also, by having multiple receivers with a DSSS system, you're less likely to experience fading due to multi-pathing. These two things would go some way to explaining the superior performance of the more expensive receivers.

Interestingly enough, the FHSS systems don't seem nearly so susceptible to multi-pathing (perhaps because the wavelength of their signal is constantly changing therefore any null-points due to reflections will be far shorter-lived) and they seem to get more than adequate sensitivity/range.

I find it interesting that (for instance) the Hitec system manages to provide what is reportedly bullet-proof control using something as simple as their 7-channel receiver with its BODA antenna while, to get the same level of security, JR/Spektrum needs an expensive 9-channel receiver and a raft of satellites.

Of course it has to be remembered that the Hitec and most of the Chinese products are using technology that is more than two years advanced over that on offer from Spektrum and two years is a *long* time in the electronics game.
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Re: FHSS versus DSSS, which is best?

Postby fernandez » Mon Jun 07, 2010 9:11 pm

Yes it has proven that f.i. fasst, airtronics, nomadio all could be used in RC speedboats, however f.i. spectrum dsm / dsm2 could not be used.
The boats create huge sprays of water, but for some reason hopping systems can cope with it.
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Re: FHSS versus DSSS, which is best?

Postby skyguy04 » Mon Jun 07, 2010 9:21 pm

Interesting that water would cause interference. Are you sure it's not the material the boat is made of? All carbon? I don't know.. i'm not a boat guy. If it's all carbon though, it would be similar to a glider application. With carbon gliders, you MUST have antenna's sticking out of the plane and they must always been seen by the transmitter. Therefore you'd need multiple antenna's sticking out of each side of the plane. I would assume that you wouldn't want to poke holes in your speed boat, so is that another reason you can't use spektrum in boats? :-)

Again, i'm purely speculating as i don't have a clue about RC boats.
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Re: FHSS versus DSSS, which is best?

Postby RCModelReviews » Mon Jun 07, 2010 10:41 pm

Multi-pathing could be a major problem with boats - the reflection of the signal from the water's surface sometimes canceling out the direct signal from the transmitter.

Frequency-hopping systems help mitigate this problem because the wavelength of the signal is constantly changing so any multipathing tends to be far more transient (shorter) in nature thus has far less effect.

It's also why some FHSS systems (such as Hitec) seem to work reasonably well with a single antenna.
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Re: FHSS versus DSSS, which is best?

Postby Bingo » Sat Jun 12, 2010 7:38 am

RCModelReviews wrote:The Spektrum does check for a clear channel before it allocates its operating frequencies so I don't see how he got more than 2 systems on a channel. In fact, if he had 40 radios, then they should all have chosen different channels (since Spektrum radios choose two out of 80 channels).

His methodology sounds suspect to me, as do his results.

Did he use a spectrum analyzer to determine whether the radios had indeed all used the same channel? I suspect he was making some rather nonsensical assumptions.


Mmm, I did not know that Spektrum radio's are tranceivers(The ability to check for clear channels would need a receiver), I was under the impression the transmitter chooses random channels and has NO receiving capability?

skyguy04 wrote:Interesting that water would cause interference. Are you sure it's not the material the boat is made of? All carbon? I don't know.. i'm not a boat guy. If it's all carbon though, it would be similar to a glider application. With carbon gliders, you MUST have antenna's sticking out of the plane and they must always been seen by the transmitter. Therefore you'd need multiple antenna's sticking out of each side of the plane. I would assume that you wouldn't want to poke holes in your speed boat, so is that another reason you can't use spektrum in boats? :-)

Again, i'm purely speculating as i don't have a clue about RC boats.


Water just like carbon fiber absorbs 2.4ghz signals - A simple test to see how "friendly" certain materials are is to chuck it in a microwave oven, If the material heats up you know it's not 2.4 "friendly".
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Re: FHSS versus DSSS, which is best?

Postby RCModelReviews » Sat Jun 12, 2010 9:03 am

Bingo wrote:Mmm, I did not know that Spektrum radio's are tranceivers(The ability to check for clear channels would need a receiver), I was under the impression the transmitter chooses random channels and has NO receiving capability

No, virtually all modern 2.4GHz transmitters have the ability (whether it's used or not) to receive as well as transmit.

The chips used (Cypress in the case of Spektrum) are transceiver chips with transmit *and* receive capabilities built into them.

Water just like carbon fiber absorbs 2.4ghz signals - A simple test to see how "friendly" certain materials are is to chuck it in a microwave oven, If the material heats up you know it's not 2.4 "friendly".

Actually water can both reflect and absorb 2.4Ghz depending on a number of factors.
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Re: FHSS versus DSSS, which is best?

Postby Bingo » Sun Jun 13, 2010 10:32 pm

RCModelReviews wrote:
Bingo wrote:Mmm, I did not know that Spektrum radio's are tranceivers(The ability to check for clear channels would need a receiver), I was under the impression the transmitter chooses random channels and has NO receiving capability

No, virtually all modern 2.4GHz transmitters have the ability (whether it's used or not) to receive as well as transmit.

The chips used (Cypress in the case of Spektrum) are transceiver chips with transmit *and* receive capabilities built into them.

Water just like carbon fiber absorbs 2.4ghz signals - A simple test to see how "friendly" certain materials are is to chuck it in a microwave oven, If the material heats up you know it's not 2.4 "friendly".

Actually water can both reflect and absorb 2.4Ghz depending on a number of factors.


Is it a fact that Spektrum does indeed do a scan? - I just don't believe it.
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Re: FHSS versus DSSS, which is best?

Postby Mr Ed » Mon Jun 14, 2010 9:01 pm

I don't remember the article that I read this in, because it was shortly after the radio came out. JR stated that the transmitter looked at the spectrum and picked two channels that were free. Now if this is the case, then JR is receiving on the transmitter along with transmitting. Wish I could remember the article, but it's been awhile and I can't remember everything. Getting old doesn't help either, but that's beside the point. The biggest reason I didn't pick JR after flying a 9303 for quite some time was that fact that I have been reading about all the problems they have been having. At first they said it just flat wasn't true and then they said the guy making the statement didn't know what he was talking about. Then they finally admitted that they had a fix for the problem. This problem was dealing with the brownout and reboot taking so long that the plane crashed before it had the chance to reboot. That tells me that they are not interested in hearing from people until they figure out what is going wrong and then come out and say, hay, we have a fix for that problem. If they can't admit they have a problem and are working on it then something is wrong. Ever since they lost a module I sent back with my transmitter I haven't trusted them. When QQ crashed at a demo, they took it in a hanger and worked on the system right away to see what had happened. It would seem that it browned out and crashed due to the heat. He had flow that same plane a few days before at home and never had a problem. When he went to the demo flight, he was at a location where it was much hotter and he got hit with a brown out and as low as he flies, he didn't have time to recover. He was flying a big plane with lots of big digital servos and they just took to much out of the battery pack. They never said anything about the servos quitting on him, just that the receiver quit and had to reboot. At the time it was taking close to 10 seconds to reboot the receiver and that is just to long. Since then they have taken steps to decrease the reboot time to something like 1 or 2 seconds now. Still, a company that won't admit that they have a problem does not foster much faith with me. I would rather have a company that admits to having a problem and tells me they are working on it rather then one that lies about the problem and refuses to admit they even have a problem. I think they are still in the pre-internet era where they can get away with saying something and not have it all over the internet in a matter is minuets.

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Re: FHSS versus DSSS, which is best?

Postby W5HYN » Tue Jun 16, 2015 9:05 pm

Yes, I know this is an old thread but...
It is interesting that Walkera recently introduced new radio systems using DSSS signaling. Their older systems used FHSS. Anyone have comment on the new Walkera DEVO systems? In the past Walkera has been primarily known for toys and were not on the RC radar. But now you can buy big multi rotor camera platforms from them and they use DSSS. Some of the new multi rotors are big and dangerous if the pilot loses control.
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