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Old Jan 19, 2013, 11:29 AM
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bigheaded5's Avatar
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2.4 Mhz whats the deal?

Im coming back into the hobby after a while away and I see everyone using the 2.4 radios now.... Can someone explain to me the idea behind them? Am I to understand they dont have channels any more? It seems like Im reading that they dont interfere with each other at all? Is there also a radio out with a TV screen on it for an on board camera? Im a bit in the dark here
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Old Jan 19, 2013, 12:18 PM
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Canada, ON, Ottawa
Joined Feb 2006
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It's true. There are no channels in the old sense. Rather, the radio uses a wide range of frequencies and spreads the information across them. Here's an explanation of how it works.
http://www.rcmodelreviews.com/spreadspectrum01.shtml

In practical terms, 2.4 is a big improvement over the previous FM systems. Most importantly, no more risk of being shot down by someone on your frequency. No long cumbersome antennas. No problems with electrical noise. Much better resistance to other kinds of interference. And radios are much cheaper and more capable.

On the other side, you do need to understand that 2.4 signals can be blocked by conductive stuff like aluminum, engines, batteries, CF, etc. and how the receiver should be chosen and installed for a particular type of model. Not difficult but different.

You also need to understand that, with certain exceptions, receivers are not interchangeable between systems. A Spektrum receiver (or clone) works only with Spektrum transmitters (or compatibles). Same for Futaba, etc.

You have some reading to do, but it's not so hard. When you have specific questions there are lots of people to offer advice (!)
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Old Jan 19, 2013, 12:24 PM
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whitecrest's Avatar
Orleans, MA
Joined Feb 2007
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Most of the new radios are on 2.4Ghz which is in the microwave band. There are channels in the sense that these systems hop from one frequency to another at a rapid rate. The transmitter and receiver are synchronized (bound) and frequency hop in the same pattern in order to communicate successfully. This technology virtually eliminates interference because each transmitter-receiver pair operating in the band is on a particular frequency for only a tiny fraction of a second, and other transmitter-receiver pairs are using the frequencies at different times.

Different manufacturers use varying methods of frequency hopping so equipment compatibility is usually confined to a specific manufacturer. There are aftermarket receivers that will work with a particular manufacturer's technology, but you must be sure to verify compatibility.
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Old Jan 19, 2013, 03:14 PM
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Quote:
Originally Posted by Daedalus66 View Post
It's true. There are no channels in the old sense. Rather, the radio uses a wide range of frequencies and spreads the information across them. Here's an explanation of how it works.
http://www.rcmodelreviews.com/spreadspectrum01.shtml

In practical terms, 2.4 is a big improvement over the previous FM systems. Most importantly, no more risk of being shot down by someone on your frequency. No long cumbersome antennas. No problems with electrical noise. Much better resistance to other kinds of interference. And radios are much cheaper and more capable.

On the other side, you do need to understand that 2.4 signals can be blocked by conductive stuff like aluminum, engines, batteries, CF, etc. and how the receiver should be chosen and installed for a particular type of model. Not difficult but different.

You also need to understand that, with certain exceptions, receivers are not interchangeable between systems. A Spektrum receiver (or clone) works only with Spektrum transmitters (or compatibles). Same for Futaba, etc.

You have some reading to do, but it's not so hard. When you have specific questions there are lots of people to offer advice (!)
Good summary.

In terms of blocked signals. The same issue existed with 72 MHz. If you put your antenna inside a carbon or metal fuselage it would block the signal and often you could not pass range check. So you ran the antenna outside.

Same thing applies here, only the antennas are very small. 72 MHz antenna was about 39" long so it was pretty hard to block it inside a non conductive fuselage.

2.4 Ghz antenna are only 31 mm long, a bit more than an inch. So the antenna can be hidden by a large battery, a motor, a fuel tank, etc. So you have to be a bit more careful about how you install the antenna. And doing a range check from several points around the plane is a good idea.

So you have some new things to learn, some old things to forget. No more frequency control, no more crystals, and no long antenna hanging out of models.


BTW, 72 MHz is still legal so if you have narrow band 72 MHz equipment you can still use it. I have both. And you are far less likely to run into interference with someone else on the same channel. But since so many have moved to 2.4 GHz, the old frequency contol disipline has fallen into neglect so just make sure you personally check with everyone when you arrive at the field. And keep an eye out for those other 72 MHz pilots who arrive who have gotten sloppy with frequency control.


Conversion: If you have 72 MHz radios that you love, and they are module based, they can likely be converted to 2.4 GHz with a module change. There are 2.4 GHz modules for Hitec, Futaba, JR, Airtronics and others.
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Old Jan 20, 2013, 01:24 AM
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One more thing not highlighted, and much more visible in 2.4G than FM, there is a lot more inter brands hate and fanboys !
Beware what you choose and how you praise after purchase
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Old Jan 20, 2013, 04:13 AM
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Sverige, Värmlands Län, Filipstad
Joined Jan 2009
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Hi,
And it is good to know that basically all major radio brands is a good choice. There are some radios that could be said to be more like "toyradios" that usually are included in cheaper ARF packages (plane, radio, motor).

If one is member of a RC club there is a tendency to use some brands of radios and that has an advantage that users can help each other with programming and such. So If You intend to be a member of a club in your area visit them and ask what radios they use.

I use Futaba myself (14MZ) and I intend to use it some more years (it came out on the market 2005). If You consider a Futaba remember that they have only two radios today that has telemetry (data from plane can be sent down to transmitter for visual and audiable alerts/presentation), 14SG and 18MZ.

Thrend is towards more and more telemetry capable radios with many different sensors (hight, variometer, voltage, temp, RPM, GPS etc).

Example of major brands are Futaba (Futaba/Robbe in Europe), Spektrum, Hitec, Jeti, Multiplex, Graupner.

Some of the radios today have very advanced programming capabilities for heli, sailplane, airplane etc. So You probably should investigate what different radios in same brands and different brands can do regarding the programming capabilites so You avoid buying a radio now that can not do what You maybe want to use in future.

If You are going to use FPV You may need do more research on selecting suitable radio since it is some special considerations with FPV.

Once You start to use a good 2.4 GHz radio You will really understand the advantages, and the disadvantages are very few, mostly to do with the reciever antenna(s) You must be more careful with so signal not get blocked to the reciever. And You do not wrap reciever in soft foam anymore, just velcro with a small velcro around its mounting plate will be OK. Most 2.4 GHz receivers are not so sensitive to vibrations since most component is surface mounted but some 2.4 GHz receivers generate more heat that old receivers back in the days and therfore should usually not be wrapped in soft foam that we used before with 27, 35, 72 MHz receivers. Transmitter antenna on 2.4 Ghz radios is usually a tiny rubber/plactis antenna that can be folded (some have the antenna built in inside the transmitter but not that many). As in old days the rule of not pointing the antenna tip towards the model in the air still apply. The antenna broad side give strongest signals so one usually fold the antenna 90 deg to one side or downwards while flying (just in case You wonder why the antenna is foldable).

You may also know there are "digital" servos today (althoug analog also still exist) and they are often faster, have better holding force (but can draw little more power) and are very precise. Digital servos are also more sensitive to linkages that is not smooth since they will then start to get a buzzing sound and draw unneccessary power and drain the battery earlier in such case. Many servos has also metal gear (or similar materiel), some servos have brusless motor to get about 5 times longer life then non brushless motors, Futaba BLS is an example of such servos but they are expensive).
There is also "high voltage" servos and that mean You can use 2 cell LiPo (7.2 volt) or 2 cell LiFe (6.6 volt) battery as power source for them (older servos may only allow 4.8 volt, or 6 volt). High voltage (HV) servos is usually used in larger airplanes like RC jets and "3D" planes etc where You need really strong servos.

I know You may have some reading to do and it might seem to be much information to digest (I know I thought that when 2.4 GHz came) but You really do not need to know so much about 2.4 GHz how it works - You can just rely on that is very good and safe system since all radio manufacturer use it now and millions of users have used it since it started to come about 10 years ago (and about 2005 more widespread) so the manufacturers and users experience on this technology is proven for years.

About a TV screen: I can imagine You want the screen not in the radio but instead an external screen separated from the radio. You or Your friends at the flying field will not be able to see so good on a screen that is built in on the radio. You can have external screen on a stand beside You or perhaps mounted on the radio (upwards) so You get it as visable as possible. FPV guys can tell You what works best from experience.
I have seen ready to fly planes with radio that has a built in screen on the radio, sutable for FPV flying, this one for example http://www.spyhawkfpv.com
(check Youtube "spyhawk FPV" and You can read reviews, flying etc)
But that radio and plane is targeted at FPV (beginners) and can basically not be used together with anything else then this plane. You probably want a generic radio that can be used for more broad applications. You probably may want a radio that can be upgraded with new software(firmware) that You can do Yourself, to get buggfixes and new features later (Futaba 8FG was a very good example of how much new features You got via new software You downloaded and installed Yourself in the radio for free during the years).
There is also googles to be used with FPV.

Good luck and I hope You find a radio You will be happy with for many years in the future!

/Bo
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Last edited by bossee; Jan 20, 2013 at 05:15 AM.
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Old Jan 20, 2013, 04:33 AM
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Philippines, Calabarzon, San Pedro
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Just to chime in.

Apparently, the data being sent is now digital. Each data packet contains the identification number of the TX as well as a checksum. Your receiver can hear everything, if there are 50 fliers in the field, it can see their inputs, it just discards the ones with the wrong ID.

I don't think it matters which one you turn on first, the RC will not suddenly fly away if there's no receiver since between the ID number and the checksum, valid data packets can't just come out of background noise.
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Old Jan 20, 2013, 05:07 AM
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Romania, Dolj, Craiova
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The receiver does not hear everything, they listen to specific channels that are changed in a sequence known only by the receiver and the bound transmitter. The channels change is done very quick, every some milliseconds.
At a moment in time, there are chances that other transmitter to be on the same channel, but the collision will be only for those 2-3 milliseconds, next hop surely the two systems will be on different channels, and the short break will pass unnoticed, because the receivers will keep last valid command.
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Old Jan 20, 2013, 08:35 AM
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LI, New York, USA
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Quote:
Originally Posted by bigheaded5 View Post
Im coming back into the hobby after a while away and I see everyone using the 2.4 radios now.... Can someone explain to me the idea behind them? Am I to understand they dont have channels any more? It seems like Im reading that they dont interfere with each other at all? Is there also a radio out with a TV screen on it for an on board camera? Im a bit in the dark here
Radio with built in screen for FPV - Spy Hawk RTF
But it is dedicated to this plane, not general purpose as far as I know.

http://www.rcgroups.com/forums/showthread.php?t=1629512
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Old Jan 20, 2013, 09:35 AM
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San Diego, California
Joined Dec 2004
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"There are no channels in the old sense. "

I'll argue that. Where I fly many, many of the "old" 72 channels ARE still used, the pinboard is there, and utilized; as for me, I will give up my 50 mHz stuff when they pry it from my cold, dead fingers, and I stil have to check, and see that no one else in on my channel. Why give up/replace perfectly good radio equipment just "keep up with the Jones's??????

Les
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Old Jan 20, 2013, 09:40 AM
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USA, TX, Trophy Club
Joined May 2002
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Quote:
Originally Posted by LesUyeda View Post
Why give up/replace perfectly good radio equipment just "keep up with the Jones's??????

Les
Les - it is not about that. I switched long before most - as I saw the huge advantages and candidly saw the most reliable RF link I had ever had in the world of RC. It is more reliable, more robust and more connected than anything 72MHz.

If it was not better you would not see people switching in droves. There is a really good reason for the switch it is simply better, much much better.

Mike
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Old Jan 20, 2013, 10:40 AM
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If one look back, I started RC in 1973 and then only 27 MHz was in use, todays 2.4 GHz is a huge step forward for signal reliability and almost everyting else. In the small RC club I was member in back then we kept track of each others 27 Mhz frequencies rather good at the field so that was really no problem for us. The problem was so and so reability of the radio, specifically the recievers and servos since they could not cope so good with vibrations as today and also the NiCd we used was not as good as the reciever and TX batteries we can use today (LiPo, LiFe, NiMh, Li-ion). Another problem was to keep track of both TX and RX battery usage - we had no (at least not in our club) any good tools really to know how much we really had left in the battery while we was out flying. We knew from experience how long it could be turned on before the servos started to go crazy because voltage got low in RX battery. And we read in manual how long radio could be used (in best of worlds) with so and so many servos.
Anyway, to get a 2.4 GHz radio today is as obvious as buying a car with electronic fuel injection - carburators are more or less history in new cars so to speak. Maybe not the best analogy but I'm sure You understand.
As far as I know if one is into FPV 2.4 GHz may have some limitations but other then that it is hard to find any practical disadvantage with a brand new 2.4 GHz radio today.
As for the signal in various 2.4 GHz systems it is differences how it is transfered but You really do not need to know that to be able to select a good radio today. Futaba had and still have a very good reputation for their FASST (and newest FASSTest) 2.4 GHz system but that does not mean it is the best system to transfer 2.4 GHz signals, it may be equal or better systems out there today. There has in the past been some problems with various 2.4 Ghz radios (Spektrum DX8 had initial problems but they made a recall for free and fixed it and new DX8 radios today do not have that problem) and even systems (like IFS that Graupner used was no hit at all and Graupner switched later to their present HoTT 2.4 GHz system). This is just examples of that there has been some problems but that is not unique for radios and 2.4 GHz, it happen in most fields from time to time. What count is how a manufacturer take care of problems if they arise.
As for service of 2.4 Ghz radios I think they require much less service then in old days but it is good to send it in for checks now and then, My Futaba 14MZ has been in for check one time during the years I have used it and I probably will have one check more before I retire the radio. TX and RX batteries need to be replaced after a while but that apply to all radios.

/Bo
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Old Jan 20, 2013, 11:02 AM
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Not all 2.4G radios use multiple channels. I have a CT6A, and it uses a single channel with a modified FSK modulation. I wouldn't doubt that some of the other cheap radios that come with RTF aircraft are the same. BTW, I didn't know this when I bought it, and the CT6B version does jump channels.
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Old Jan 20, 2013, 12:19 PM
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Quote:
Originally Posted by LesUyeda View Post
"There are no channels in the old sense. "

I'll argue that. Where I fly many, many of the "old" 72 channels ARE still used, the pinboard is there, and utilized; as for me, I will give up my 50 mHz stuff when they pry it from my cold, dead fingers, and I stil have to check, and see that no one else in on my channel. Why give up/replace perfectly good radio equipment just "keep up with the Jones's??????

Les
You seem to have taken that quoted sentence way out of context. He wasn't saying that the "old" FM channels weren't still available to use, he was trying to explain the main difference between the 72 MHz world versus the 2.4 GHz world in as much that you aren't using a single assigned channel anymore like you do when on 72 MHz.
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Old Jan 21, 2013, 09:42 AM
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San Diego, California
Joined Dec 2004
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"You seem to have taken that quoted sentence way out of context. "

Not out of context, just out of my quick read understanding:-)))))))))))))))

Les
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