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2.4. range greater than 72

Old 05-25-2013, 02:06 PM
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spirit pilot
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Default 2.4. range greater than 72

Im hoping someone can settle a debate. One of our club members claims that 2.4 has a greater range than 72. does anyone know for sure?
Old 05-25-2013, 04:05 PM
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baronbrian
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Default RE: 2.4. range greater than 72

To my knowledge, the shorter the wavelength, the more energy needed. I believe 72mhz has a longer range, but there are many variables. Both are good for as far as you can see your plane, plus some. Add 2.4ghz's superior interference attributes and I would much rather have the 2.4, even with less range than the 72.
Old 05-25-2013, 04:08 PM
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Default RE: 2.4. range greater than 72

Ask him what range his eyeballs have. It's definitely way less than the radios, either band.

Andy
Old 05-25-2013, 06:22 PM
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Default RE: 2.4. range greater than 72

Tell him to get two planes and fly them untill they crash and then note the distance. If max power is allowd for each type of radio, I would go with 72. In the 70's and early 80's 72 radios like Kraft put out max power but when narrow band came they started limiting the TX output. Probably better freq tuning did not require as powerful a TX. 2.4 is set to the needed range and no more, but if you had problems with internal antennas on 72, 2.4 is probably better.
Old 05-25-2013, 06:52 PM
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Default RE: 2.4. range greater than 72


ORIGINAL: AndyKunz

Ask him what range his eyeballs have. It's definitely way less than the radios, either band.

Andy
Amen. Range is plenty for both.

Ifly giant scale and even then if you're out 1,500 feet the question is . . .Why?

Ialso have a little F-86 Sabre with 15" wingspan and someone commented that the AnyLink is useless because of the 1,000 range. At 1,000 feet Icouldn't SEE the model let alone guess its orientation. At 400 feet it is a little silver blur.
Old 05-25-2013, 09:28 PM
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Default RE: 2.4. range greater than 72

I've flown 72 MHz out to a mile.
Never considered trying it with 2.4G

On a related note: Receiver sensativity is far more important that Transmitter output.
In the end though range is range and the system has to work together.
Old 05-26-2013, 04:13 AM
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Default RE: 2.4. range greater than 72

He's wrong, 72mhz has longer range, all things being equal.
Old 05-27-2013, 07:02 AM
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warbird72
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Default RE: 2.4. range greater than 72

lol!! Good one.. I never fly so far away that I can't see my plane/heli. Bit I did however break the trust issue with 2.4 on range! I went to harbor freight and bought an 80 dolled piper cub. I installed a Hitec 2.4 RX and converted my eclipse 7! It will fly farther than you can see it..
Old 05-28-2013, 06:38 AM
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LesUyeda
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Default RE: 2.4. range greater than 72

"He's wrong, 72mhz has longer range, all things being equal. "

Technically accurate. Due to the shorter wavelength of 2.4, the scattering effect caused by interfering object is greater; including the ground, people, and anything else you can imagine.

Les
Old 05-29-2013, 11:59 AM
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sidgates
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Default RE: 2.4. range greater than 72

In the '70s & '80s the FCC limited power to 3/4watt to the final RF stage and probably still do. My tests years ago showed that once you were over 39 inches above ground range on 72MHZ was pretty much limited by how far you coud see the model. Once I tested a Royal radio on 27MHZ with the receiver layer in the dirt, it was solid at one mile, stopped the test at that point.

Appox a year ago I wanted to range check a XPS on 2.4GIG so I did the same test on a Futaba 9Z and a Hitec 2.4GIG. With the receiver approx 36" in the air I got solid control on all 3 sets at .91 miles. That was as far as I could go line of sight.

Most of the 72MHZ sets in the 80's had less than .50 watts to the final RF including Kraft.

I heard of one local flyer who flew out 5 miles on 2.4GIG, but I don't know what brand the radio was for sure. He had an observer on the ground follow the model to stay legal.
Old 05-30-2013, 06:48 AM
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Default RE: 2.4. range greater than 72

I would think wth FPV flight becoming more popular that range would be more of an issue. The guys that fly miles out use an antenna booster to do so.
Old 05-30-2013, 06:53 AM
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Default RE: 2.4. range greater than 72


ORIGINAL: raptureboy

I would think wth FPV flight becoming more popular that range would be more of an issue. The guys that fly miles out use an antenna booster to do so.
If you can't legally fly out beyond visual range, what does Extended Range matter?
Old 05-30-2013, 03:57 PM
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Default RE: 2.4. range greater than 72

You can easily 1-3 miles on a modern TX with .75 watts.
The range is more dependent on the sensativity of the receiver than the power of the transmitter.

Legally per who? If your not a AMA member then??
(I am a AMA member and dont BTW), but am a bit of a RF freak who understands this stuff.
Old 05-30-2013, 06:41 PM
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sidgates
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Default RE: 2.4. range greater than 72

I think the AMA rule for FPV is you have to have a spotter who can visually take over and fly the model in case of a problem. I don't know what they would say about the spotter following the model in a car and keeping the model in sight while the FPV pilot flies out 5 miles.
Old 05-31-2013, 02:06 AM
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Default RE: 2.4. range greater than 72

Aye, RX sensitivity is most important since max. output power is set by regulations.

http://www.digi.com/technology/rf-ar...er-sensitivity


Unfortunately, manufactures do not publish the specific RX data.

An typical example is Horizon/Spektrum with an exemption:

http://www.horizonhobby.com/products...-plug-GWSRX4SB

Old 05-31-2013, 02:12 AM
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bogbeagle
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Default RE: 2.4. range greater than 72

A couple of years' back, I tested my 35 MHz gear out to 2,200 yards ... with both Rx and Tx held at waist height, across a gentle valley.

That's about 6 times the distance at which I can safely fly a 60" model.



Never checked the range of my 2.4 gear, though.
Old 05-31-2013, 06:16 AM
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Pippin
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Default RE: 2.4. range greater than 72

...quite interesting:
http://www.webx.dk/rc/RX-measurement...let-listen.htm

"RF sensitivity dBm/uV:
both represented in dBm and in voltage, better sensitivity means a lower input signal was needed for 50% signal to noise ratio (10dB SINAD)
a -110dBm receiver is 6dB better than a -104dBm type, for each 6dB better sensitivity you will get double the range -
if you don't have any other factors like noise on the power supply line. If you have a receiver with less than -90dBm sensitivity
you will have a 500-800 meter range with most transmitters, this will give flips and range problems..
suggestions: always look for at least -100dBm if you fly outside."
Old 05-31-2013, 06:54 AM
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Default RE: 2.4. range greater than 72

ORIGINAL: Pippin

An typical example is Horizon/Spektrum with an exemption:

http://www.horizonhobby.com/products...-plug-GWSRX4SB
ARG! Please! That's a GWS receiver, not a Spektrum! And it's very insensitive!

We just happen to sell it!

Andy
Old 06-03-2013, 05:01 PM
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JPMacG
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Default RE: 2.4. range greater than 72

Path loss is proportional to frequency squared. So the 2400 MHz link is much more difficult than 72 MHz. The 2.4 GHz designers had to go to a lot of trouble to make the system work... polarization and spatial diversity, processing gain from the spread spectrum signal, etc.

The ideal system in terms of range would be spread spectrum at a lower frequency.
Old 06-04-2013, 09:25 AM
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Default RE: 2.4. range greater than 72

ORIGINAL: BuschBarber
ORIGINAL: raptureboy
I would think wth FPV flight becoming more popular that range would be more of an issue. The guys that fly miles out use an antenna booster to do so.
If you can't legally fly out beyond visual range, what does Extended Range matter?
As far as I know there are no current laws or regulations restricting FPV or other far away flying. Some of the FAA activities we have read about could establish laws or regulations about it, and I honestly think they should.

AMA has FPV guidelines for what is covered under their insurance policy and I think something pretty similar should have the force of law behind it.
Old 06-04-2013, 10:06 AM
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Default RE: 2.4. range greater than 72

Sport Flyer magazine recently did a range check comparison with the popular 2.4ghz systems... all are beyond line of sight but the winner was the Hitec AFHSS system, although they actually ran out of room to continue to test to get the exact number but it was still connected at 6.3 miles! FYI: Both Futaba FAAST and Spektrum DSMX were good to 4 miles.

Mike.
Old 06-04-2013, 05:16 PM
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Default RE: 2.4. range greater than 72


ORIGINAL: JPMacG

Path loss is proportional to frequency squared. So the 2400 MHz link is much more difficult than 72 MHz. The 2.4 GHz designers had to go to a lot of trouble to make the system work... polarization and spatial diversity, processing gain from the spread spectrum signal, etc.

The ideal system in terms of range would be spread spectrum at a lower frequency.
You are correct. However the spread spectrum systems have much better sensitivity. I have read SS can give as much as 40db processor gain.
You cannot get enough bandwidth at lower frequencies. You would wipe out most existing communication systems.
I dont know why we dont have a 900ms system. I guess he IC's are just too expensive.
Old 06-04-2013, 06:40 PM
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Default RE: 2.4. range greater than 72


ORIGINAL: dirtybird


ORIGINAL: JPMacG

Path loss is proportional to frequency squared. So the 2400 MHz link is much more difficult than 72 MHz. The 2.4 GHz designers had to go to a lot of trouble to make the system work... polarization and spatial diversity, processing gain from the spread spectrum signal, etc.

The ideal system in terms of range would be spread spectrum at a lower frequency.
You are correct. However the spread spectrum systems have much better sensitivity. I have read SS can give as much as 40db processor gain.
You cannot get enough bandwidth at lower frequencies. You would wipe out most existing communication systems.
I dont know why we dont have a 900ms system. I guess he IC's are just too expensive.
900 Mhz. is a problem child band. There is so much going on there (much like 2.4) but you're in a frequency range where you're not quite pure line of sight. Where terrain, trees, buildings, distance and even the nature of the frequency can help block all the congestion on 2.4, not so much at 900. 900 does have some penetration ability so interference sources much farther away can cause problems than with a 2.4 system. Also, on 900 you're dealing with a much greater diversity of modulation types than on 2.4 where it is almost 100% pure digital. I wouldn't trust an RC system on 900 ...... but I once said that about 2.4 so wouldn't say it couldn't be done. You are spot on about greater cost on 900. Also, not a lot of license free spectrum available on 900 to further complicate the problems.
Old 06-04-2013, 07:08 PM
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dirtybird
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Default RE: 2.4. range greater than 72

Why would diversity of modulation types cause any problems? All would just look like noise to a SS system. And if it didnt have the correct code it would just get rejected
Old 06-04-2013, 07:22 PM
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Default RE: 2.4. range greater than 72

I've seen it happen many times where a traditional SS system will just shut down when overcome by excessive interference. If you can't get your desired signal through on enough of the spread slots, the system will simply not function correctly. Newer modulation schemes such as OFDM get around this quite nicely.

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