2.4 GHz Radio

[bluefish]

Has anybody tryed the new 2.4 GHz radios from Futaba, is it any better in water? or does the higher Hz lower it's water penetration!

[aeroengineer1]

The theory says that with

The theory says that with this change in order of magnitude higher in freq the penetration should be lowered. I have heard similar reports as well. THere is a thread about underwater reception where there is a link and the topic was treated in a little more detail. Please note that a change of something like going from 2.4 to 5.8 is not going to have a great effect, but going from 75 mega hertz to 2.4 giga hertz will.

Adam

[JWLaRue]

Adam is correct. The folks

Adam is correct. The folks who have been experimenting with transmitting video from onboard cameras back to the shore via 2.4GHz wireless have consistently reported that once the antenna goes below the surface, the signal is lost.

Quite frankly, this trend in the r/c industry to move towards the 2.4GHz spectrum is troubling for us sub-surface folks. While the flyboys and target folks can all get along fine with this new technology, we could well find ourselves without an r/c transmitter/receiver that will work with our subs in the not too distant future........

-Jeff

[mylo]

At this point in time,

At this point in time, what is THE radio to have for sub use ?

Mylo

[JWLaRue]

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.

[mylo]

Jeff, thanks for that, but

Jeff, thanks for that, but I should have been more specific in my question.

Which radio /freq. will allow for the best (most consistant trouble free) AND deepest sub operation ? Is 6' of depth in a clear, fresh body of water attainable ?

Does anyone hold the depth record ? ......AND controlling the thing to the surface under it's own power after attaining that depth ? (I know, I know...they ALL sink REALLY well).

Thanks.

Mylo

[ramius-ii]

Hi Mylo!

Hi Mylo!
There are a number of factors, more than just frequency. The antenna, for one is a BIG consideration. Most R/C units are using a "fractional" antenna. That is 1/4 wave lenght or 1/4 of what the antenna should really be. Then there is the power you are running. Most transmitters are limited in power output available. The only way to overcome this is to go to a directional antenna, similar to what most people use for television reception. Antenna's are "rated" in DB (decibels). For every 3 DB of "gain", you have effectively doubled your transmit power or receive "sensitivity". The problem is that our subs are small and a "yagi" antenna is not practical and we are stuck with a "whip" antenna or, at best a dipole (two sided) antenna. The Navy uses antennas that are 160 and 80 meters in lenght. At this lenght you are almost better off with a "wired" control.
The resonant frequency of water is 2.4 GHZ. Most microwave ovens operate at this frequency. This means that a transmitter at 2.4 GHZ will only warm the surrounding water and the signal will not escape when submerged. If you wish to transmit a signal from underwater, then the highest frequency that will work is 1.2 GHZ.

This I know for two reasons. First, I presented the problem of transmitting a video signal from underwater to a friend who does antenna designs for the U.S. military. Second, based upon an antenna design he gave me, I tested this at a depth of 1 meter at a horizizontal distance of 150' using test equipment from my work (Fox Television). I sent what are called "color bars" as this signal with indicate potential problems such a "phase shift" or what some people call "the green adder" as the picture wants to turn green and the other color will be wrong.

The next part of successful transmission of picture is to have the antenna directly connected to the transmitter. Just to give you an idea of this here is a picture. The "mounting plate" is designed to act as a reflector as most fish in a lake do not have receivers.

Hope all this helps and is not to "technical" or confusing.

Best, Ed

[warpatroller]

It would appear that lower

It would appear that lower frequencies will penetrate deeper into the water. In that case theoretically, 27Mhz should have a deeper range than 75Mhz...and 75Mhz deeper than 2.4Ghz. The radio antenna carried by Uboats (the single cable running to the bow and the twin cables running to the stern) was suppose to transmit and receive signals in the 3Mhz to 30Mhz range...quite a low frequency.

The single bow cable was for transmitting and the twin stern cables were used for receiving. I'm thinking of attempting to use the stern cables on my model for my boats RC receiving antenna. Though to make them usable for this purpose, the wires would probably have to be larger diameter than correct scale size.. Something to experiment with when I get to that point on my project.

Steve

[ramius-ii]

Hi Steve,
You are basically

Hi Steve,
You are basically correct. At 27 MHZ a full lenght antenna would be some 17 feet long! At 75 MHZ it would be 1/3 the lenght or about 6.3 feet long. Of course you are using a fraction of the lenght such as 1/4 or 5/8. There is another "trick" which is to use a "loading coil" which causes the transmitter or receiver to think the antenna is physically longer than it is.

Best, Ed

[mylo]

Steve,

I was wondering if

Steve,

I was wondering if the antanae lines couldn't be used for.....antanae.

Ed,

My 1:25 type VIIc/41 is 8'9" long, so maybe the antanae wire wouldn't be too terribly out of scale looking, as well as actually being long enough. My stern antanae are about 4'. Can the two be paired up to make one long antanae of about 8' ? ....in which case, would it function well using 75 Mhz ?

"IF" all this worked, is an operating depth of 6' realistic ? (clear fresh water)

This whole transmitting/receiving/antanae under water thing has had me baffled since I first started looking into R/C subs.

Mylo

[Guest]

To be honest, radio range

To be honest, radio range has never been an issue for me.

The boat is out of site, or too deep to be any fun before you start getting any signal problems.

I use 40mhz, which is the legal FM surface band for UK, Europe, Japan and I believe Australia too. Some modellers also use the trusty old 27mhz AM band , although you'll be hard pressed to purchase a multi-channel set on that band these days.

Brackish or salt water presents a problem, as can heavily chlorinated pool water. However you would need some very exotic radio kit to get around the problems experienced in those conditions... or add a very long aerial that remains above the water at all times.

For models I am building at the moment, I will fit Schulze receivers-

http://www.modelflight.com.au/schulze_receivers.htm

These feature built in signal conditioning which is very worthwhile for model subs. Small and decently priced too.

Andy[/url]

[mylo]

Is there a radio on

Is there a radio on the market that gives you a warning when the signal is getting weak ? ....a small LED that comes on perhaps, letting you know BEFORE you totally lose the signal ?

It seems to me that guys are installing some sort of fail safe that "Blows the ballast" when the signal is lost for a certain number of seconds. Is this a feature of the radio, or some other electronic gizmo ?

What is the benefit of a higher freq then ? ....even for surface r/c operation of planes/boats/ etc. ?

.... I don't want to stray off topic of the thread, but these questions are coming to me thinking of this radio thing.

Mylo

[carcharadon]

bluefish,

The limitations of your submarine

bluefish,

The limitations of your submarine are probably more of a concern than the ability of your submarine to receive signals underwater (in freshwater). I would be more concerned about keeping the electrics dry.

I run two versions, a 7 foot and 4 foot submarine, and both have been down at least 30 feet. I use a HiTec four channel for both subs, without any problems and have used a Futaba AM as well without any problems.

http://www.youtube.com/watch?v=ntKT1araF3U

[mylo]

30 feet !!!

.....yep, that's deep

30 feet !!!

.....yep, that's deep enough.

Mylo

[ramius-ii]

Hi Mylo!

Hi Mylo!
The answer to your question is yes. The antenna design you would use is called a "folded dipole" and is quite common. How it is constructed is the center point of say the bottom most wire is cut and becomes the feed point. The rest of the wire is the antenna. So you have starting from the center, the wire that goes towards the bow. Then, that wire is connected to a continuous lenght wire going towards the stern. When this wire reaches the stern, it heads back to the center point. It would look as if it were the letter "O" and a piece of the bottom of the "O" were cut and the "O" had been sat upon. One wire becomes the center of your coax and the other, the shield or ground. Typically these antennas are 300 ohms and a Balun or RF transformer is used to match the impedance of the transmission wire (usually 50 ohms). The unit used for television antennas going from "round" wire to "flat" wire is close as it is typically 75 ohms and you are not transmitting, only receiving.

About fail safes, there are two types commonly used. One is a lost signal type, the other is a pressure sensor that only allows for a ceratin depth to be reached. At sea level, atmospheric pressure zero point, the pressure is 14.7 PSI, or what is called "one atmoshere". Every 33 feet of depth, another 14.7 psi pressure occurs.

"A submarine's depth ratings are a primary design parameter and measure of its ability. The depths to which submarines can dive are limited by the strengths of their hulls. As a first order approximation, each ten metres (thirty-three feet) of depth puts another atmosphere (15 psi, 100 kPa) of pressure on the hull, so at 300 metres (1000 feet), the hull is supporting thirty atmospheres (450 psi, 3000 kPa)."

Hope this helps,

Ed