Sport_Pilot

UAV's don't require 2.4 except possibly for short ranges when taking off or landing.  They use other frequencies for long range.

loadthis

My Feedback: (3)

Agreed
[link=http://www.ntia.doc.gov/files/ntia/publications/2003-allochrt.pdf]FCC Frequency Allocation Chart[/link]

Sport_Pilot

Sorry but this is about the article, and the article is about the frequency, not the technology. And the 2.4 band is apparently overcrowded in metro areas, at least per the article, so this discussion should not involve the viability of spread spectrum.

Dave

TO  SILENT-AV8R

In November 2009 issue of Model Aviation on page 23 the author of R /C Soaring at the Nationals reports:"Overall Soaring had just approximately 30% of the registered pilots flying on 2.4GHz" !
Must be a reason?

ira d

Also transmitters use less battery power to operate on 2.4 at least that is what I have noticed.

Greenfuelboy

My Feedback: (60)

I have noticed that a lot of the larger sail planes are Carbon Fiber and 2.4 does not transmit through Carbon Fiber very well. So FM with an antenna works better in some cases. I lost my 50cc gas plane due to 2.4 failure. The company tried to blame it on optical kill switches. Yes I had a solid power supply, all of my stuff was new. I did not use a optical kill and it failed still. I have used my 2.4 radio and can duplicate the process with my gas engine. I have used it with nitro and electric and no problems. I have tested it with a junk plane with my 50cc gas engine. It seemed to have no problems. I flew and got several good flights and it browned out on the ground, I was lucky. I just will not use my radio with gasoline engines again. Just goes to show brand name radios can be lemons too.

Kwesdog

This statement is not entirely true but comparing military grade to a home built FPV system is apples to oranges. Not going to give out technical details but I have been flying military UAS since 2004 (in Afghanistan now typing this) and some line of sight (LOS) systems use 2.4ghz with directional antennas out to a couple of hundred kilometers.

Harry

Sport_Pilot

I don't know about that, but they have better batteries so that is what you may have noticed.

Sport_Pilot

As I said they use it for short range.

Kwesdog

200+ kilometers is not short range. Much farther than that and you get into beyond line of sight (BLOS or otherwise long range) systems which indeed use other freqs but they also involve sat relay systems or high power systems that bounce signal off of layers in the atmophere.

Short range applications will typically use an omni configuation in the UHF band with high output antennas so don't stand too close to UAV's that are operating for long periods if you want to have kids. 10 kilometers or less would be short range which several SUAS can safely handle.

But back on topic.

I have to agree with what has already been stated in the thread earlier. If the 2.4 issue was such an issue than it would reason that safety would be a major concern. How many 90 size helis are out there flying with 5+ foot rotors disks of death on 2.4? How many 33-40% airplanes that could go out of control and do major damage to property or maim/kill someone are on 2.4? Scale turbines flying 150+ MPH on 2.4?

To me it sounds like hog wash and not because there is not some new technology out there but rather if it was safety related and the AMA held onto this secret information I would have to question why I bother paying dues to yet another entity who would put corporate profits ahead of the well being and safety of the dues paying members.

Sounds more to me like the heads of state (Companies) are working with the AMA and waiting till their new product line is about ready to hit the shelves before making an annoucement that will be put under the guise of safety to push the new product. No different than when the glitch free 2.4 marketing blitz began other than this time with the secret meetings it would seem that the AMA is in line for some kickbacks.

Thats pretty much what my summary of this thread has come to.


Thanks for reading

Harry

cj_rumley

The article is about the frequency, Sport. That's what is fundamentally wrong with it. The real difference between R/C radios operating in 2.4 GHz band and the old 72 MHz stuff is spread spectrum, so while the article ignored the 'value added' by it, any halfway intelligent discussion of the relative merits of the signaling systems being compared must consider it. I'm not going to write a primer on SS here, there are on-line sources for that. Just a couple of summary items for interested folks to consider:
-The robustness of the control link isn't a just matter of signal strength (S) at the receiver as the author argues or at least infers. It is a function (S) to noise (N) ratio S/N.
-SS provides gain in S/N by sending the same information, redundantly, multiple times into different 'slots'. Copies of the same quantum of info (say a binary bit) are sent to different slots, separated by time and/or frequency. Processing in the receiver sums the energy received in all of the slots, and by a decision algorithm declares that signal is present or not - simple binary yes/no, 1or 0 decision. Intelligent signal (S) is detected in more slots than would contain energy due to random noise (N), so the effective S/Nincreases. That is processing gain, the whole objective of the SSsignalling scheme.
-Sending multiple copies of every quantum of info takes similar multiples of bandwidth - the more redundancy (and robustness)the more bw. That bw simply isn't available in the part of the RFspectrum allocated to us between a couple TVbroadcast channels (72 MHz). That's why 2.4 GHz, not because conditions for propagation of radio waves is better there.
Way oversimplified, but Ihope that does't distort the how/why of the process too much........

Sport_Pilot

Sorry I read that as 200 meters. I did not know you could operate 200 Kilometer line of sight. I would have thought the curveture of the earth would have caused unrealistic .

However 200 kilometers and line of sight is still somewhat short range for modern UAV's. But the fact that UAV's use 2.4 at that range and there will be even more UAV's when the FAA gets their new regulations in effect, then that supports the article.

Sport_Pilot

The article isn't about staying at 72 Mhz either.  It is pushing for a whole new set of frequencies.   However, while sperad sprectrum may or may not be viable for 72 Mhz, frequency hopping would.   But that was not what the article was about.  The issue is how busy the 2.4 spectrum is or soon will be.   Lots of stuff coming so need to start pushing for this now.

Silent-AV8R

Soaring was slow to adopt mostly due to the fact that in 2008 many of the high end planes had 100% carbon fiber fuses. Check the NATS in 2011. Or consider the Visalia Fall Soaring festival. 200 individual pilots with close to 300 entries (multiple classes) I believe there were around 25 or so not on 2.4. You still see a few holdouts, but that is mostly driven by cost of conversion, not worries about performance.

Silent-AV8R

Consider that the standard TX pack used to be the 9.6 volt 8-cell pack. Many 2.4 radios use 4 or 5 cell NiMH or 2S lithium packs. Overall I think the technology behind the electronics is allowing for lower voltages to be used.

on_your_six

My Feedback: (11)

You know that wireless phones, and wireless routers run on 2.4 ghz. Some of that technology is also running on 5.8 ghz. I would think that the same rules apply as secondary users of the bandwidth.

I would not be surprised to see 5.8 ghz come into use for RC control. I do know one thing, I refuse to fly my $2500 planes when another flier is using the $50 radio & $10 receiver from hobby king. I just don't trust them.... YET!

I have an EE background and am a ham.

cj_rumley

The basis for author's argument against 2.4 GHz is so basically flawed as to provide no sensible rationale for moving to a whole new set of frequencies or for that matter changing anything else.

Frequency hopping is simply one technique used to implement SS. The 72 Mhz band allocated to R/Cis about 1 MHz wide, just enough to accomodate the existing channels. My Spektrum radio can choose to operate anywhere in a 1 Mhz band - its choice based on the noise environment it sees, not mine. As Isaid, SS(including frequency hopping) requires redundant data transmission, ergo more bandwidth, or time (that's where the latency issue comes in, inextricably linked but a whole topic of its own). Where is that additional bw going to come from? What keeps a FHR/Csystem on 72 Mhz band (or any other band) from stomping on existing users?

warbird72

My Feedback: (79)

I just read the whole artical.. Man you all are scaring me..I just started changing over to 2.4. Now what ?? I have to go back to 72 to get a good signal or what..

ira d

It's not the battery i'm sure of that.

Silent-AV8R

Keep doing what you are doing and enjoy yourself.

ira d

2.4 is working very well for a lot of flyers and is better than 72 in many ways, One thing we can count on if 2.4 starts to become a problem we will read about
it here on RCU and like forums long before we read about it in Model Aviation. I'm not degrading MA by my statement just stateing my observation.

804

My Feedback: (1)

As someone who went 2.4 back in early '08 with Spektrum DSM2, and have thousands of trouble-free flights with it,
I would say buy the system of your choice, follow the manufacturers recommendations carefully,
be careful in installations and diligent with power (battery) systems,
and go have fun.

Oh, and filter all the static in this thread very carefully.
There is a lot of noise, and little useful signal.

Sport_Pilot

Frequency hopping was used a long time ago to prevent jamming of the earliest weapons systems. Used electo-mechanical relays and tubes I think. It does not require spread spectrum to be used.

That said, there are channels in the 72 and 75 band that are no longer used for beepers I believe, and there may be others in the whole range that could be adopted. Theremay bemany radio systems that are not being used, at least not in the volume that they once were.

Sport_Pilot

I don't see where the article said everyone should move away from 2.4 immediately. It seems to be supporting another frequency other than 72 that is used only for RC.

Sport_Pilot

They are using lipo batteries in them now, so it is at least part of the reason.