cloudancer03

My Feedback: (22)

man all this diatribe over fm and 2.4 sheesh. either way is perfectly safe and reliable..be careful you dont fall going to the bathroom and get a brain hemmorhage..its remotely possible right???

give it a break.I love my radios but I like to go with the new technologies also.2.4 is here to stay and whatever issues they have and I suspect minor the hobby is better for it. I remember how we had to fight with the feds to get the high bands on 72 so we wouldnt get shot down by a half crazed CB'er or trucker wanting to jack up his 27 mhz signal. remember 27 guys it sucked!

relax and enjoy the hobby ..our hobby is safer today than its ever been.

dbcisco

You can't compare wattage because it is radiated energy. The energy received from a radiant energy source is inversely proportional to the square of the distance from the source.
Our 1 watt max. radios are only twice as "loud" as a 32 milliwatt transmitter. A 100mw transmition can easily interfere with a 1w signal.
This reminds me of trying to explain how a 200 watt amplifier is only slightly louder than a 100 watt amplifier. You need a 10,000 watt amplifier to be twice as loud as a 100 watt amp.

nonstoprc

My Feedback: (90)

To interfere a frequency hopping scheme, do you need 100mw transmission on each and every channel of the 2.4G?

dbcisco

You will glitch on the frequency(s) that have interference.
Even if one frequency has interference, that is a .4 second loss of control. In that .4 seconds a plane traveling at 50 mph will have travelled about 100 feet (twice the length of an average house, the length of my entire yard, 10 car lengths etc.)
A lot can happen in that distance/time.

dirtybird

My Feedback: (5)

You certainly can compare radiated wattages. It tells you how far away a system must be before it is no longer a problem. A wifi or bluetooth need only to be near the horizon. So if you stay away from the city you will be well clear of those devices.
Our radios are limited to 100 mw on 2.4GHZ

dirtybird

My Feedback: (5)

To completely block a frequency hopping system you need 100mw on all frequencies on all channels. That is why the military liked it. It takes a lot of power to stop it from getting a message through.
Remember a channel is 1mhz wide. Blocking one frequency within that channel won't do it. You have to block all 1 million of them. Then there are 80 channels.

dbcisco

Sorry, but you are very wrong everything you just wrote.
Where are you getting these silly ideas?
Wattage in and of itself tells you very little unless you can do exponential conversions in your head. I have no clue what the horizon and cities have to do with anything seeing as a "horizon" can be anywhere from 100' to several miles.
The maximum RC TX pwer is 1000mw also refered to as 1 watt.

drakenn

My Feedback: (2)

Umm... 50 MPH is 2,648,000 feet per hour.. so thats 4400 feet per minute... 73.33 feet per second or 29.33 feet in .4 seconds. About 10 yards. Considering the human reaction time is about .5 seconds from visual sight to reaction...

On top of that Futaba's FASST system: "Other 2.4GHz systems hold firm to one or two frequencies, increasing the potential for interference. The frequency of Futaba 2.4GHz FASST shifts hundreds of times per second, so there are no signal conflicts or interruptions – and no need for a frequency pin! "

Lets just assume 100 times per second... interference on 1 channel results in less than 1 foot of movement without control and that's assuming the entire band is spammed to the point of no signal getting through. Spektrum locks into two bands... and I have watched heli's fall out of the air due to interference at large events. Never seen it happen with Futaba. The Joe Nall event had 4 spectrum heli's down all seeming to be complete radio lockout. They would come up over the hill that is behind the heli pilots and just fall out of the air.

dirtybird

My Feedback: (5)

JIMF14D

Just go fly! No one cares if you graduated from kindergarden here!

Yikes!

dbcisco

50 Miles per Hour = 73.33 Feet per Second = 29.3 feet in .4 seconds. We both miscalculated in our heads. Paper works better.

Quick, what is the 12th root of 2 ? Mozart could probably have done this in his head, I can't. I doubt you can either.

There is no "normal" horizon in reality. My horizon changes drastically as I just walk around the block.

From the FCC bulletin "UNDERSTANDING THE FCC REGULATIONS FOR LOW-POWER, NON-LICENSED TRANSMITTERS":

2.4-2.435 GHz Spread Spectrum Transmitters 1 Watt Output Power

2.435-2.465 GHz Spread Spectrum Transmitters 1 Watt Output Power

2.465-2.4835 GHz Spread Spectrum Transmitters 1 Watt Output Power

dbspl

A 1 watt transmitter has 14.9 dB higher output than a 32 mWatt transmitter. It has nothing to do with being "twice as loud", but it does have everything to do with the square of the distance from the source. The radiated energy falls by 6 dB with every doubling of distance.

dbspl

BarracudaHockey

My Feedback: (11)

None of this confused the issue for the original poster I'm sure

dbcisco

I used "loud" as a directly related term that people could comprehend. Yes, dB is the information needed and originated in the field of audio engineering, thus "loud" is very apt even though "you" can't hear it.

dbcisco

Missing something in your explanation regarding distance. RE: If I am a foot away from my plane and then move two feet away the decibels are down to 8.9, then I move four feet away and it drops to 2.9, then eight feet away it is less than zero. Does that mean that I can't fly any plane more than 8 feet from my TX?

I know what you are trying to say (I think) but I doubt anyone else here does.

BarracudaHockey

My Feedback: (11)

Oh I dunno, I worked on avionics on P-3's for 12 years including SS, encrypted, satalite and other communications, navigation, and electronic warefare systems.

I'm just staying out of it because it doesn't help the guy trying to fix the noisy engine

As a product reviewer I've had to drop any notion of brand loyalty and realized a long time ago that the major brands, for the end user, all work pretty darn well.

dbcisco

For the following let "maximum distance" be the distance at which the RX stops responding to the TX on level ground.
To make this as simple as possible, at half the maximum distance of your 1 watt radio your original signal is about the same as a 32 milliwatt radio. At 3/4 the maximum distance the signal is equivalent to a 5 millwatt radio.

If you double the distance of the RX from the TX, the receiver will get the square root of the previous signal.

If at 10 feet from the transmitter you get a signal of 100 then at 20 feet you will get a signal of 10 then at 30 feet you will get a signal of 3.16 then at 40 feet you have a signal of 1.8 and at 50,1.33 and so on.

JIMF14D

True, by now the guy with the noisy engine probably fixed things, made 10 flights and had a beer. The best part he did not miss much here with the battle of the brands.

I did not sleep at a Holiday Inn last night but I did convert my several year old Kyosho PT-17 to 2.4ghz with a Hitec 7 channel Rx and my old Eclipse 7 with the $20 Hitec conversion module. Idid a range check and stopped walking at 200+ paces as I was getting lazy and the guy waving his arm behind my plane was getting small.

Seemed to fly fine and Idid not even need my slide rule or my db cheat sheet to know when to land.

Jim D

Rodney

I'll have to go along with Dirtybird, he has said it quite well. And yes, "watts out" is everything if you are comparing range with the type of antenna most 2.4 systems use. If your receiver has a fixed sensitivity (and it has) the range in inversely proportional to the square root of the distance between the transmitter and the receiver, i.e. if you double the distance between the two, it will take 4 times the power from the transmitter to give the same sensitivity. He is also correct in that frequency hopping is much more difficult to interfere with than the other systems (which means more immune to interference).

dbcisco

Yup. I think we were trying to make a very complicated mess of engineering as simple as possible...and failing miserably.
The reality is that 2.4Ghz is not perfect. Maybe it is better than FM but for many it isn't needed and for a few it presents problems that don't exist with FM. The other thing I discovered is that a great many people adore 2.4Ghz without rhyme nor reason. What ever makes you happy is fine by me.

dbspl

The decibel is a power ratio, it has no absolute value unless a reference is specified. In the above example, 32 mWatts was the reference. The output gain of a 1 watt transmitter referenced to 32 mWatts is 14.9 dB. At the distance where the ouput has fallen to 0 dB means that the level at that distance is 32 mWatts. Given that typical 2.4g signal can be discerned down to -80 dBm (.00000000001 watt), you probably have quite a distance left to go before you have to worry about loss of signal.

nonstoprc

My Feedback: (90)

Futaba 2.4g tx hops the frequency faster than .4 sec interval. So where does the .4 sec/channel come from?

In my field, one guy lost two airplanes with the fixed 2-channel 2.4G system. On the 2nd incident, the receiver is brand new from the vendor. Both planes were down at a location known to cause trouble to FM.
There are no known plane loss involving true frequency hopping systems.

So from practical point of view, frequency hopping systems do have an advantage.

FrankWilliams

My Feedback: (13)

Why is the OP using a 4.8v receiver pack when Spektrum says to use no less than a 6v pack? While, it's not likely the cause of frustration, it can't be helping any.

JIMF14D

It is my understanding that all RC TX are 100mw max. I know Hitec says A9 is that.
Jim D

nonstoprc

My Feedback: (90)

I do not know if low voltage was a factor in the two crashes. But logically it should not be, because of location dependency.