2.4 GHz Radio

[aeroengineer1]

Please do a search for

Please do a search for the thread on the antinuation of a signal under water. There is something in the engineering world called orders of magnitude. It means 10^n. So lets say that we start with 10 and we want to compare it to 1000. 10 is 10^1 and 1000 is 10^3. If we subtract the powers of 10 we find that 1000 is 2 orders of magnitude greater than 10. When we talk in terms og our radios 75 mega hertz is 75 * 10^6 and 2.4 giga hertz is 2.4 * 10^9. So moving the decmal around we get 7.5 * 10^7 and 2.4 *10^9. We see once again that these are 2 orders of magnitude off. If I remember the nnumbers correctly it was a change in the signal antinuation of about 10 dB. This is off the top of my head between the 2 that are compared. If we compare anything in the range of 1 * 10^7 and 9.9 * 10^7 (10 - 9.9 mega hertz) the antinuation difference was under 1 dB if I remember correctly. So we can see that going from 27 to 75 is not going to really create a big effect on the signal, but going from 75 mega hertz to 2.4 gigahertz is going to hurt.

Adam

[aeroengineer1]

Here is the link to

Here is the link to the thread, it was on the almost exact same topic. http://s181686668.onlinehome.us/phpBB2/ ... oards.php5
and here is the link to the article http://www.qsl.net/vk5br/UwaterComms.htm

Adam

[ramius-ii]

2.4 GHZ

Hi Adam,
Excellent research and you are very correct. My point in previous post has to do with antenna lenght. The formula for antenna lenght is 11810/Frequency in Megahertz Times .96 (the velocity factor). (11810/Fmhz * .96) Thus a 1/4 wave antenna at 27 MHz would want to be 105" long, while a 1/4 wave antenna at 75 MHZ would be 38" long. 38" which is much easier to deal with in a scale model than 105".

2.4 GHZ, actually 2.45 GHZ, is the frequency used in microwave ovens as it is a compromise between the resonant frequency of water molecules and the ability to penetrate the food. If we used the actually resonant frequency of the water molecule then a signal would never travel.

The other problem with 2.4 GHZ is that the cell phone company Nextel is now moving cellular telephones to this frequency making the frequency or "Band" very crowded!

Best, Ed (WB6NSN)

[aeroengineer1]

Ed,

No that was not

Ed,

No that was not directed at you, but the other questions about frequencies that were in the same order of magnitude. Sometimes people have a hrd time with this concept. The see that the frequency is doubled and so it should be better or worse for water penetration. I was just trying to clarify.

Adam

[ramius-ii]

Hi Adam!

Hi Adam,
Not a problem, I did not read you post this way. I only wanted to add to what you wrote so anyone who read our posts would have "well rounded" understanding from multiple view points.

Best, Ed

[mylo]

So far, I fail to

So far, I fail to see how 2.4Ghz is better for any r/c application, and as for subs, it's definately worse.

That antanae length formula could come in handy. Does an antanae not have to be straight to be effective ? How do they work at all when they are packed inside a WTC in anything by a straight line ? ....maybe a guy should just be happy with the answer, "Don't worry about it, it does." ....but it seems the right guys are on this thread to ask this question.

Mylo

[JWLaRue]

So far, I fail to

So far, I fail to see how 2.4Ghz is better for any r/c application, and as for subs, it's definately worse.

Signal propogation issues aside, the higher frequencies allow more data to be transmitted over a given period of time. This could (also) include adding data redundancy checks along with the data being sent to ensure that what was transmitted is what is received.

In the world of data networking, this is a very good thing.

-Jeff

[ramius-ii]

Hi Mylo!

Hi Mylo,
From a “technical” standpoint, we are only concerned with the “electrical” length. I am sure you have seen antenna’s on cars with a black tube in the middle, towards the top, or on the bottom. This black tube contains a length of wire that is “coiled” to cause the transmitter or receiver to think the antenna is physically longer than it is. As for shape, the shape does have some impact and it is not very much. Mostly it is how close is the antenna to metal. When you take a wire, such as an antenna, and place it next to something metallic, you now have a capacitor. A capacitor is two pieces of metal separated by an insulator. For antennas, the result is you lower the frequency where the antenna is most effective. In your stereo, you have speakers that can be 4 ohms or 8 ohms. If your stereo is designed to feed a 4 ohm speaker and you use an 8 ohm speaker, what happens is that there is an “impedance” mismatch. Will the speaker work? Yes. However, then full amount of electrical energy is not being used and what is not used is converted to a very small amount of heat.

For a simple dipole antenna (two wires stretched out away from each other) the impedance is 300 ohms. As we bring the two wire to a closer angle to each other, the impedance changes and approaches 50 ohms or less! Antenna design, to be perfectly honest, is way beyond my understanding. We usually call this a “black art” and refer such matters to those who specialize in the type of engineering. While I do have some understanding, I usually ask a ham radio friend who does antenna designs for a living for solutions.

Jeff is correct, and not because of the actual transmitted frequency. The amount of data in an FM system is directly related to the “bandwidth”. In FM we have a center frequency and we shift or change this frequency through a process called “modulation”. Modulation causes the transmitter to transmit both below and above the center frequency by a given amount. Thus a transmitter at 100,000 hertz with 5,000 hertz deviation will produce a signal from 95,000 hertz to 105,000 hertz. If we wish twice the data or information, we need more bandwidth so we would choose a transmitter that would vary from 90,000 hertz to 110,000 hertz. In television, 6 MHZ is necessary for all the picture information. In two-way radio, 2.5 KHZ is all that is necessary. I sure hope I have not confused or offended anyone.

Best, Ed

[Wheelerdealer]

2.4 Ghz seems to be

2.4 Ghz seems to be the way to go if your getting a new radio for anything other than subs. http://2.4gigahertz.com/features/features.html
Not having to buy any crystals, not having any frequency clashes are the most attraction features to me. Stuff like reduced latency are more important to racers and flyboys.

[bigdave]

Many folks are taking a

Many folks are taking a good look at (and buying) the Polk Tracker III. This is a synthesized frequency radio which means you'll never need to worry about channel conflict again....even at the SubReagtta. This unit is available in a number of air and surface frequencies for both North America, Europe, and (I believe) elsewhere.

-Jeff

p.s. I must admit that I'm using a Multiplex Royal EVO due to the dead-easy programming.

p.p.s. Blame Big Dave for my......affliction.

Sorry for your affliction Jeff. Multiplex fever is very contagious.
I am on my forth one now!! Help!!!!! BD.

[JWLaRue]

BD,

Not a problem. It's quite

BD,

Not a problem. It's quite a benign afflication.

-Jeff

[mit]

As a practical observation I

As a practical observation I have a HAM radio licence (WR1H) and I have used my 50 Mhz set for Subs (I am allowed) and I have found it to be superior than my new Spectrum DX7. My range is practically double on the lake with my 50 Mhz JR set.

This is again just pratical observations.

Nick

[mike dory]

Guy's, just to amplify what

Guy's, just to amplify what Nick said, The other great advantage is generally, there ARE no other radios operating any where close to the Ham (6 meters) band. This is great. This all but eliminates interference (accidents) from your fellow Sub captains. Getting your license is well worth the investment in time. Best Wishes Mike Dory (WD6GIR)

[anonymous]

So far, I fail to

So far, I fail to see how 2.4Ghz is better for any r/c application, and as for subs, it's definately worse.

That antanae length formula could come in handy. Does an antanae not have to be straight to be effective ? How do they work at all when they are packed inside a WTC in anything by a straight line ? ....maybe a guy should just be happy with the answer, "Don't worry about it, it does." ....but it seems the right guys are on this thread to ask this question.

Mylo

Being the one here who flies RC jets I an to tell you they are excellent. No flag to post. Just go to the field and fly your aircraft without fear of interference or waiting for the frequency. No one can turn on their radio and send your bird to the deck or cashing into a human being. Far better. Best reason of all. With so many idiots in the hobby this takes away the risk of idiot-ency!

Steve

[mylo]

Ahhh yes....idiot-ency, I forgot about

Ahhh yes....idiot-ency, I forgot about that. Good point.

Mylo