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Old Jul 28, 2012, 10:51 AM
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Originally Posted by sertav View Post
Unbelievable that they would even think of letting LS interfere with GPS. EVERYBODY uses it. Military, commercial aviation, long haul trucking, shipping, police, fire, EMS, surveying, cartography, geology, everyday auto navigation, etc.

Compared to LS/GPS debacle, the R/C hobby is hardly even a microscopic speck of poop from a fly on that elephant...



Lovely... Would that crash everyone in the vicinity flying 2.4Ghz? If so, at what kind of range?
That depends on a lot of things. The 40 Mhz-wide FM TV transmitter & 10W frequency-hopper could take out a lot of stuff on adjacent channels - depending upon the quality of the receivers' front-ends, distance to the interferer, the local noise-floor, and the actual frequencies of other 2.4 GHz transmitters in the vicinity of the receiver in question. The SSB signal, being only 3 kHz wide, would be less-likely to cause problems - unless it was close enough to cause front-end overload. (The first amplifier stage in most receivers has to deal with every signal that makes it to the antenna - from VLF though microwaves - so out-of-band signals can overload the front-end of most receivers, if the transmitter is nearby and/or has higher power or a high-gain antenna.)

BTW - we did lots of interference testing back in the 90s when my students & I built our own 2.4 GHz RC system with a 15-mile range. Was a fun & educational project.

Joel
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Old Jul 28, 2012, 10:56 AM
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Originally Posted by turboparker View Post
That depends on a lot of things. The 40 Mhz-wide FM TV transmitter & 10W frequency-hopper could take out a lot of stuff on adjacent channels - depending upon the quality of the receivers' front-ends, distance to the interferer, the local noise-floor, and the actual frequencies of other 2.4 GHz transmitters in the vicinity of the receiver in question. The SSB signal, being only 3 kHz wide, would be less-likely to cause problems - unless it was close enough to cause front-end overload. (The first amplifier stage in most receivers has to deal with every signal that makes it to the antenna - from VLF though microwaves - so out-of-band signals can overload the front-end of most receivers, if the transmitter is nearby and/or has higher power or a high-gain antenna.)

BTW - we did lots of interference testing back in the 90s when my students & I built our own 2.4 GHz RC system with a 15-mile range. Was a fun & educational project.

Joel
I'll bet that was a cool project. You must have been pushing some decent wattage to get that kind of range.
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Old Jul 28, 2012, 11:05 AM
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I'll bet that was a cool project. You must have been pushing some decent wattage to get that kind of range.
Aren't there guys going out that far with DragonLink at, what, 1/2 watt? Of course that's not 2.4 GHz... it's 433MHz, right?
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Old Jul 28, 2012, 11:10 AM
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Originally Posted by turboparker View Post
unless it was close enough to cause front-end overload. (The first amplifier stage in most receivers has to deal with every signal that makes it to the antenna - from VLF though microwaves - so out-of-band signals can overload the front-end of most receivers, if the transmitter is nearby and/or has higher power or a high-gain antenna.)
Since we are OT anyway , doesn't the front end usually have a band pass filter to reduce this ?
Won't help with in band sources, but should stop things like 1 watt 72 mhz transmitters.
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Old Jul 28, 2012, 11:17 AM
Gopher huntin' stick jockey
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I'll bet that was a cool project. You must have been pushing some decent wattage to get that kind of range.
Yeah - it was the most popular class project that I ever came up with. My students even bugged me to come in after-hours & on Saturdays to work on it! Regarding the power - we were running 1W with a 10 dBd gain transmit antenna at 25' AGL, and a unity-gain whip on the aircraft. Our video link was the weak-point. We were running analog amateur television (ATV) @ 3W on the 440 MHz ham band, and ran out of range at about 3 miles.

Joel
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Old Jul 28, 2012, 11:17 AM
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Aren't there guys going out that far with DragonLink at, what, 1/2 watt? Of course that's not 2.4 GHz... it's 433MHz, right?
Well, you're going to get much longer range propagation with lower power output at lower frequencies. The ELF (extremely low frequency) antenna system used to communicate with submarines is amazing and that's all I'll say about that.
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Old Jul 28, 2012, 11:22 AM
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Since we are OT anyway , doesn't the front end usually have a band pass filter to reduce this ?
Won't help with in band sources, but should stop things like 1 watt 72 mhz transmitters.
Yes - well-designed front-ends do have good filtering. Unfortunately - a tight front-end is usually the first thing that gets axed in low-cost receiver designs. Also - band-pass filters are far from being created equal. It's one of those YMMV things....

Joel
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Old Jul 28, 2012, 11:31 AM
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Yes - well-designed front-ends do have good filtering. Unfortunately - a tight front-end is usually the first thing that gets axed in low-cost receiver designs. Also - band-pass filters are far from being created equal. It's one of those YMMV things....

Joel
In your opinion, what's the best 2.4Ghz R/C link system currently available? Please say DSMX because I'd really like to stick with Spektrum. Too much hardware to switch over...or cannot be switched over...
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Old Jul 28, 2012, 11:55 AM
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Yes brown outs are the weakness of the spectrum-jr radio system....It is how the chipset is designed and how much power it needs to operate...There is a gap in the boot of the cmos on the chip which is a few nano-seconds..without a cmos you have no control of the loops inside the chip or anything else inside the chip like the pre amp...The spectrum system seems to do a clean re-boot from scratch on power up if it is a certain power drop or a complete power loss....
If you run out of gas, is that an engine problem?
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Old Jul 28, 2012, 11:58 AM
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In your opinion, what's the best 2.4Ghz R/C link system currently available? Please say DSMX because I'd really like to stick with Spektrum. Too much hardware to switch over...or cannot be switched over...
Spek is great for anything you want to do. All of these systems are so good it's impossible to say what is best. Look at features of the programming and mechanics of the radios to find what's best for you, because the argument over which signal style is best will never end.
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Old Jul 28, 2012, 12:07 PM
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If you run out of gas, is that an engine problem?
No, but If it happens whenever you turn left with the tank still half full, then it is a system problem

There is no denying that Spektrum was more prone to problems related to momentary voltage drops causing models to crash then other 2.4 systems, and even previous mcu based 72 mHz systems. Their early stuff took 5 seconds to reboot.

Pat MacKenzie
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Old Jul 28, 2012, 01:19 PM
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No, but If it happens whenever you turn left with the tank still half full, then it is a system problem

...
I wholeheartedly agree. But I wouldn't solve that problem by installing an engine that can crank up again in 1 sec instead of 2. I'd fix the fuel pickup line in the gas tank.
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Old Jul 28, 2012, 01:33 PM
Southern Pride
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Best 2.4 system is yet to be determined but IMO it is not Spektrum,JR or Hi Tech.

I have Spektrum DX7 (orginal) , HiTech AFHSS , Fly Dream and Fr Sky ACCST . I use Fly Dream and Fr Sky in my three Ace Micro Pro 8000 Transmitters because I truely believe they desire the best available and to date I have not been able to determine which of these two are truely the best. The FrSky does provide great Telemetry however in fact I use Telemertry very little. I also feel that it provide the greatest range under the worse conditions but then I only fly within my vision limits and rarely at crowed events so have to base this on testing done by others.

Charles
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Old Jul 28, 2012, 01:50 PM
Gopher huntin' stick jockey
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East Bethel, MN USA
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Originally Posted by sertav View Post
In your opinion, what's the best 2.4Ghz R/C link system currently available? Please say DSMX because I'd really like to stick with Spektrum. Too much hardware to switch over...or cannot be switched over...
Sertav,

I don't know. A particular system may have a a slight edge over another in a certain situation, but the opposite may be true in another situation. As Jaz mentioned - pick the system that has the features you want. I also stay away from the cheap, off-brand receivers in aircraft that I care about, and/or those which are fast/large enough to hurt anything if they get shot down.

Joel
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Old Jul 28, 2012, 02:18 PM
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I also stay away from the cheap, off-brand receivers in aircraft that I care about
I do not have any aircraft that I do not care about and I understand the dangers to myself and others full well but IMO inexpensive does not mean cheap. Both of my prefered 2.4 systems I listed above are a lot less expensive than my Spektrum or HiTech receivers but I place absolute faith in them .

My Spektrum DX7 does have one relly great feacture that is missing in other 2.4 systems that being model match and it of course works with all of the E Flite / HH / Blade aircraft whicjh many of us seem to hvae several or more of.

Charles
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