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Old Nov 28, 2011, 11:32 AM
Rocky Mountain High and Higher
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72MHZ VS 2.4GHZ Range

I couldnt find an appropriate forum to post this so I thought here would be good and beginners can benifit.

This is a very basic question, and something I never really thought about over the years.

Q: Has anyone every attempted to see if there was any real difference in transmitting/receiving range between the 72MHZ FM and 2.4GHZ SS systems?

Not factoring in interference or antenna position in model.

Thanks,

Ace
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Old Nov 28, 2011, 01:05 PM
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SW PA
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Hey PROACE,
My only experience regarding 72MHz & 2.4GHz is with my (2) Dynam Hawkskys. I have one of each freq. & on the farm where I fly, there are no power lines, transmission towers, or any kind of interference. I have flown both them at distances where they were just a dot & no issues with either. I'm sure there are technical parameters that would probably indicate the 2.4 with better ranges. Since I find no need to go any further than I can see, both have worked for me.

Denny
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Old Nov 28, 2011, 02:05 PM
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Theoretically the higher the frequency the shorter the range. As Denny noted, in the RC application any of the popular/legal frequencies will fly a plane to the limit of the pilot's ability to stay oriented. So for all practical purposes there is no difference in range for normal RC flying. Now, FPV may be different all together depending upon how far the disembodied pilot flys from his physical location.

Larry
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Old Nov 28, 2011, 02:24 PM
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Quote:
Originally Posted by PROACE View Post
Q: Has anyone every attempted to see if there was any real difference in transmitting/receiving range between the 72MHZ FM and 2.4GHZ SS systems?
It depends on the receivers used, both have receivers that are designed for various classifications of planes including indoor flyers (very limited range), parkflyers (limited range, but basically somewhat farther than eyesight) and larger planes (unlimited range, can fly well beyond eyesight limitations). I've heard plenty of stories of people flying 72 mhz by binocular with a full range RX. The same can be done with 2.4 ghz.
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Old Nov 28, 2011, 04:36 PM
Rocky Mountain High and Higher
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Just wondering since the largest wingspan sport plane has been 80 inches but that was AM years ago. Some 2M gliders I have flown until they appeared very small.
Since I have done everything else RC and free flight I thought altitude would be a new adventure, so this winter I plan on building a 120" sailplane.
The reason I asked about range tests is that as frequency goes higher it is more effected by attenuation from moisture in the air and more dependent on line of sight and antenna polarization, thats why are 2.4GHZ recievers have diversity reception and we lay transmitter antenna down a little horizontal. I could easily build and add a signal preamp to the reciever but that adds a little weight and more battery requirement, and to add a signal amplifer to the transmitter would violate FCC rules.
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Old Nov 28, 2011, 08:50 PM
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The FPV guys regularly push these systems to the range limits, and the general rule is 2.4 is no where near the range of 72MHz, and the lock-out problem is the kicker... if you're going for range, don't use 2.4. However, if you're flying LOS you will be more than fine with 2.4 as long as you're not shooting for altitude records with giant gliders.

There have been many practical tests done on 2.4 systems and from what I gather, your maximum range is about a half a mile under average conditions. Here's an example of one such test - not very scientific, but people do test this stuff.

NightFlyyer's RANGE TEST of HIS RC radios. The results. Spektrum AR-6110 2.4 GHz , Hitec & more.. (9 min 40 sec)


All the radios were tested under similar conditions, so it gives you an idea of the relative performance of each, but it doesn't give you a hard number for what the range might be under more realistic conditions.

And yes I realize the video doesn't agree with what I said there, but he's not using good quality 72MHz stuff.
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Old Nov 28, 2011, 09:55 PM
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Jasmine, great video. Considering ground absorbion of signal and a 72MHZ signal has has an optimum height of approx 6.5 ft and 2.4GHZ just mere inchs with the correct antenna those guys results are probably fairly accurate. So in conclusion I would bet any of those radios could double distances with aircraft in flight or more with the plane in sight.
And my question has been answered.
Another question what is lock-out? Can't say I have ever heard of this, got my attention.
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Old Nov 28, 2011, 10:19 PM
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Computer receivers have two problems which can result in a lengthy loss of control. The first is that they don't fail gracefully under power supply brown-outs, while 72MHz analog receivers typically fail more gracefully. The result of that problem is usually minor glitching on 72MHz analog receivers, but it can cause a re-boot of the receiver for computerized types (which includes all 2.4 GHz and some 72MHz).

The second problem occurs when the signal has been lost - in this case the 72MHz analog stuff also tends to degrade more gracefully, slowly losing the signal - like TV used to be on a stormy night. With 2.4GHz (and digital TV, btw) if the signal is lost long enough, the receiver needs to reacquire the the signal, which is a somewhat complex process. Spektrum has dealt with this issue partially with their QuickConnect system, but that feature has limited applicability at the edge of range, where signal losses may occur for longer periods of time. The time delay to reaquire is the lock-out period, and it can be anywhere from instant (QuickConnect) to several seconds for a full re-acquisition.

With 72MHz analog stuff, your plane starts glitching a little bit and you raise the radio up over your head and fly back in closer.
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Old Nov 29, 2011, 12:20 AM
Rocky Mountain High and Higher
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Been there, done that more times than I care to admit considering the number of years I have flown RC. LOL
This lock-out sure got my attention on the 2.4 which is understandable. At least most of the times a recovery from being shot down on 72MHZ can be done, kind of my motivation for moving to 2.4GHZ. Even though it seems everyone follows the frequency rules, there is always one idiot who thinks it doesn't apply to him/her until someone else is yelling OH $H..T
Never thought about it but there might be a division in modelers on who likes which best.

I really appreciate your help openning my eyes to this issue but then again I should have done my own homework, shame on me.
If you have anymore tidbits I'll listen! and I thought I knew everything, over thirty years in the model airplane hobby and still learning.
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Old Nov 29, 2011, 01:03 AM
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Hackensack, MN
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I have a friend who is a deputy of the local sheriffs office.
The county recently switched from the usual 42/72/155 Mhz
bands to a newer system on a "much higher" band (he wouldn't say).
Bottom line is he said they started having problems with
range, especially in hilly country. Not that we fly our planes
in hilly country, but it does make you think.....
And my old Bearcat 800 XLT scanner won't pick up county
x-mits anymore....
CF
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Old Nov 29, 2011, 01:04 AM
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2.4GHz is still way better for most stuff you ever need to do. If you install and use it properly, you'll have fewer problems overall. If you're doing long range stuff you might look into the 433 MHz UHF systems, but for most stuff you wouldn't need that. Most everyone around here uses Spektrum, JR, and Futaba, with a few picking up the Hitec lately as well. There is no frequency conflict or anything - hundreds of these radios can share the same frequencies at the same time.
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Old Nov 29, 2011, 09:07 AM
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For a quantitative amount, 72Mhz under "normal" equipment and conditions should range 2-3 miles. It's LOS though so it will degrade significantly with obstacles.

Truth be told when it comes to RF signals the receiver makes one huge heck of a difference. I would bet a sensitive enough receiver would pick up a 72Mhz signal 5+ miles out. You won't have those in a typical RC plane though

Either way, as others have said, flying by sight you'll lose visual on the plane before reaching the limit of either band.

I fly my planes on 72Mhz and have never had any issues with it.
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Old May 31, 2014, 09:14 AM
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Nobody seems to be addressing the fact that strong WiFi links and everything under the sun is using 2.4GHz. I think in the U.S. the max power for 72MHz is 1 watt and for 2.4GHz it is .1 watt. Also, microwave ovens use 2.4GHz because it is efficient (resonant) at heating water. Why is that important? Your eyes (being mostly water and sensitive to radiant energy) can be slowly permanently damaged without you feeling it by this frequency. It is a matter of range vs power. The more power, the farther away you need to be to not damage your eyes. Hotels, restaurants, etc have large hidden antennas, some 5 feet tall, to make people happy with WiFi coverage. If you are looking in the direction of that wall or ceiling, your eyes are being damaged without you knowing it. Nobody cares because, hey, I have a signal! With enough power it will cook you like a microwave oven...before then you will be blind. The 72MHz tends to pass through your body. What does that do? The ONLY reason for the switch is because companies have a plan to acquire as much bandwidth as possible for smart phones, etc. They plan to take all of the TV frequencies as well. They are nearly maxed out now. There will always be a physical natural limit to bandwidth. 72MHz gobbles much more (50 channels available) than 2.4GHz (80 channels available). In the end, it is always about the money!
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Old May 31, 2014, 10:36 AM
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Originally Posted by 9Mach View Post
Nobody seems to be addressing the fact that strong WiFi links and everything under the sun is using 2.4GHz. I think in the U.S. the max power for 72MHz is 1 watt and for 2.4GHz it is .1 watt. Also, microwave ovens use 2.4GHz because it is efficient (resonant) at heating water. Why is that important? Your eyes (being mostly water and sensitive to radiant energy) can be slowly permanently damaged without you feeling it by this frequency. It is a matter of range vs power. The more power, the farther away you need to be to not damage your eyes. Hotels, restaurants, etc have large hidden antennas, some 5 feet tall, to make people happy with WiFi coverage. If you are looking in the direction of that wall or ceiling, your eyes are being damaged without you knowing it. Nobody cares because, hey, I have a signal! With enough power it will cook you like a microwave oven...before then you will be blind. The 72MHz tends to pass through your body. What does that do? The ONLY reason for the switch is because companies have a plan to acquire as much bandwidth as possible for smart phones, etc. They plan to take all of the TV frequencies as well. They are nearly maxed out now. There will always be a physical natural limit to bandwidth. 72MHz gobbles much more (50 channels available) than 2.4GHz (80 channels available). In the end, it is always about the money!
Perhaps foil hats would mitigate the problem.
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Old May 31, 2014, 11:18 AM
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Dude, don't freak out... as long as nobody is flying a microwave oven at your field, you're gonna be fine. Wi-Fi isn't gonna take out your bird. It deliberately cooperates with us.
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