Futaba Fasst vs Spektrum radio link

[GooseF22]

You have to understand the difference in electronic terms between persistance and noise. Proponents of frequency hopping will say that you would have to use alot of power and span a wide bandwidth to knock it down, but that does happen with harmonics. the issue with locked freqs is that if noise hits it, you have to burn through above the noise threshold. In radar theory, we use both, but to burn through, a narrow bandwidth is always used because it doesn't lose any accuracy if its above the threshold, and a transmitter can radiate more effective power if its not hopping freqs, thats physics. So with spektrum, they emit a large signal on two channels, with farly narrow bandwidth, but not overly narrow, but since the processing is not amplitude based, or contengency signal based, noise doesn't slow it down. Im not familiar enough with the inner workings of FASst to comment at the processing level.

[d_wheel]

	Quote: Originally Posted by GooseF22
	So with spektrum, they emit a large signal on two channels,

They are both DSSS. They both transmit their data in bursts, but FASST changes frequency between these bursts. They are both limited to 200mw average output. Why would Spektrums signal be any "larger" than FASST?

Later;

D.W.

[GooseF22]

because average output is area under the curve, so if you can narrow and stabilize frequency, you can effectively radiate more effective power with the same pulse. thats about the limit of my knowledge

[somethnextra]

So basically the FASST has wider bandwidth/lower output and Spektrum has narrow bandwidth/higher output?

[d_wheel]

	Quote: Originally Posted by GooseF22
	because average output is area under the curve, so if you can narrow and stabilize frequency, you can effectively radiate more effective power with the same pulse. thats about the limit of my knowledge

What "curve" are you referring to?

If FASST was FHSS, and we were using much higher data throughput then there might be a difference. However since they are both DSSS and the data being sent is relatively small, the power can be the same. I am not saying that they are, but I don't see any reason they can't be the same power output.

Later;

D.W.

[GooseF22]

I would have to use an analizer to measure RMS power versus peak power. dont have access anymore to it. I retired last week.

When you plot signal output, its usually measured in RMS "root mean square" or about 70 percent peak, and the area is then calculated to determine power, versus peak power.

kinda like the stereo wars where amps say peak power 200 watts, 50 watts RMS...

Anyway, Im not sure about his with spektrum, so I will stop there as there are alot of you guys smarter than me on it. I just have a basic practical working knowledge of spektrum only.

I do know this though. we worked with a 2.4 video transmitter, and it locked the fasst system out, and as long as you turn it on before the DX7 transmitter it worked fine. but that is a specific case.

my best to all
goose (retired!!) heading back to American airlines now.

[d_wheel]

	Quote: Originally Posted by GooseF22
	I do know this though. we worked with a 2.4 video transmitter, and it locked the fasst system out, and as long as you turn it on before the DX7 transmitter it worked fine. but that is a specific case. my best to all goose (retired!!) heading back to American airlines now.

It is not a good idea to use a 2.4ghz video system with any 2.4 radio system. Mine causes problems with Spektrum, XPS, and FASST. Doesn't make any difference which was turned on first, it still causes my Spektrum to lose about 80% of it's range during a range check. Range on the FASST and XPS were cut by about 50%. I had to go to 900mhz video to get any of my 2.4 radios to work full range. 900mhz does not affect the FASST at all. With XPS and Spektrum, the range is decreased about 20% with the video transmitter turned on.

All of these checks were made with 200mw video transmitters. With a video transmitter that is "legal" for public use (I believe it is rated at less than 1 mw), none of the 2.4ghz systems were effected at all.

Later;

D.W.

[sweetpea]

The question I have on that.........will your 2.4 video system do the same if I fly 2.4 in the pilot box near you?

[GooseF22]

thx
we are coming to the same conclusion. Last week john tested a new autopilot that links on 900 Mhz to the ground, and leaves the 2.4 video open. It has a very minor delay, but not too bad for a test bed, and has great range, and if the signal is lost, the autopilot just brings it back to you. pretty cool.

[GooseF22]

	Quote: Originally Posted by sweetpea
	The question I have on that.........will your 2.4 video system do the same if I fly 2.4 in the pilot box near you?

Pea, it shouldn't. the problem is on the aircraft swamping the receiver.

[d_wheel]

	Quote: Originally Posted by sweetpea
	The question I have on that.........will your 2.4 video system do the same if I fly 2.4 in the pilot box near you?

With my system, the only airplane effected is the one with the video transmitter installed. However, if I am flying a 72mhz radio with 2.4 video, and someone with a 2.4 transmitter is within 10 feet of my video receiver, the receiver gets wiped out. The ground monitor shows horizontal lines only.

It appears that if someone wants to use video at a field where there is any 2.4 activity at all, they need to move to 900mhz.

Later;

D.W.

[Zeeb]

	Quote: Originally Posted by sweetpea
	The question I have on that.........will your 2.4 video system do the same if I fly 2.4 in the pilot box near you?

D*mn good question Sam...

I'm feeling better about it after seeing Goose's answer, but I'm gona have to chew on it for a bit...

I say that because one of the guys I fly with has an electric powered Cub with the DX-7 system and when he bought the video system for it, the manufacturer told him he'd have to go with the 900 stuff for the video when using the 2.4GHz for his flight control. So his system shouldn't affect my 2.4 at all, but the stuff is getting more popular.

He's only flown it once as it's still in the "get everything working stage", but the video system makes his servos hum when it's turned on. They seem to work okay, but that tells me there's some "extraneous" signals getting into stuff they shouldn't.