2.4ghz Antennas ?

[Reckless]

okay... bit of a newbie question... I know I can't touch the length of the little silver ends of the 2.4 antenna's (futaba FASST twin ant RX)

but can I lengthen the covered wire part itself?

the reason I am asking is I kinda wanna use my 2.4 for my sub(s). now I don't plan on any static diving stuff... just dynamic, I also don't have the need or want to go anymore then 12inchs below the surface

so I'm wondering if I can lengthing my antennas use a lil clear antenna tube(s)that stick up 12inch above the sub... the tubes ofcourse will also give me indications of the location and depth of the sub


maybe I should go read the FASST manual again ... I tried a search of the forum .. but well... I suck at picking search perameters :(

[Ghost 2501]

if you want to go subsurface, 2.4ghz is not the way to go, get yourself a 75mhz 4 or 6 chan set instead

[Reckless]

I've heard of people extending the 2.4 antenna for a bouy... was thinking either a antenna tube... OR carve out a 1/144 Foam destroyer or patrol boat of the IJN variety to use as a towable or 'bouy'

just been staring at some of my nearly completed projects and thinking how to get em running with what I have (1/144 gato sub... airboat... refit toy flying sub...)

[CeeJay047]

Strikes me as a mighty small coax to mess with.

[Shaun Hendricks]

2.4ghz stops at the waters surface and heats the water a near infinitessimal amount. Your sub will stop receiving signals once it goes underwater unless you want to run a 'bobber' which, of course, gives away the position of the sub. On the plus side, if you have enough reel, and your sub sinks, you can retrieve it by the bobber.

An inexpensive AM or FM rig will probably get you better results than a 2.4ghz one.

Now, if you're set on antennas, any common wireless ethernet device's antenna also runs on 2.4ghz.

[Reckless]

okay... I know that 2.4 stops working subsurface. this is why I'm trying to find out how people have extended their 2.4 antenna to get up to the bobber/float/bouy... I would like to make like a 1/144 scale IJN destroyer something of those lines ... and tow it like it's 'hunting' the sub. I don't have a whole lot of wish to go down 4ft and sit or much lower then maybe 1ft below the surface. and I kinda would LIKE to have a marker for my sub LOL. I'm just doing dynamic diving stuff right now so I think they might work for me....

as I said at the start I know I can't touch the silver end bits.. but the rest of the wire supposidly can be shortened or lengthed.. but I don't know if it's 'wire' or Coax?

[LtDoc]

Measure the length of those 'silver end bits'. Increase their length by using odd multiples of that length, 3, 7, 21, whatever, times their length. It shouldn't mess up what the receiver is 'seeing' when it looks at the antenna, sort of. Won't damage the receiver at any rate.
If you try using coaxial cable to 'extend' the antenna you will be 'barking' at the wrong tree. Coax cable small enough for that type of use (RG-178 ?) is so lossy at 2.4 Ghz that even a few feet of it is like not having an antenna at all.
The best advice I've seen so far is switching to a different frequency band radio system. The 2.4 Ghz band is sort of like trying to use a cell phone under water, and the cell phone is three times better than 2.4 Ghz in that regard, sort of. (And don't try using a cell phone under water... sounds terrible.)
- 'Doc

[Reckless]

woot! a real answer... thanks :D

yeah I'm not trying to say that 2.4 is a good choice for subs... just that maybe in this case it might work

I've also seen that 2.4 does penetrate water... like a couple feet TOPS and not that far from the operater... not nearly trying to reinvent the wheel... just that an oval can work too... just kinda bumpy ;)

my '2nd' sub is a flying sub and it runs on 27mhz... I've got a 3rd in the works and it'll be ALOT bigger so I'll be more likely to run it father away and deeper and it'll definately be on 'conventional' radio

but this lil 1/144 gato I think I'm gonna atleast try some ideas with the 2.4 ...

in Futaba's Manual they list the wire part of the antenna as "coaxial" .... so maybe I'll have to do something in the way of an antenna tube instead of trying to lengthen the antenna .. but I have heard of people doing it just no info :(

[Julez]

A guy here in Germany submerged his submarine in a 5m deep swimming pool, and was still able to control it with his DX6.
So I would leave the antennas in the hull first, and check how it works, before trying anything else.

[LtDoc]

Reckless,
I really think that is you are going to extend that antenna you might try the 'odd multiple' thingy first. As long as the 'multiple' is an odd number, it sort of 'fools' the receiver into thinking it's the original length. This deals with the electrical characteristics of 1/4 wave length antennas and their reactance/resistance/impedance as seen by a receiver. That's not exactly the 'true-est' explanation for what happens, but it's close enough for the average person who isn't a radio nut.
Now for some of that 'radio nut' stuff.
Antennas are measured in wave lengths or fractions of wave lengths, how far the signal actually travels in one full cycle. The higher the frequency of that signal, the shorter the wave length. There are particular lengths, or fractions of that wave length that have electrical properties that are sort of easy to use in a circuit. Considering the characteristics of the other thingys in that circuit, some particular lengths can 'fit in' better/easier than others (ain't as hard to figure!). One of those 'particular' lengths is a 1/4 wave length. That 'length' changes according to the frequency being used. At 27 Mhz a 1/4 wave length is something close to 9 feet. At 75 Mhz, about 3 feet, and at 2.4 Ghz only 0.0975 feet (1.2 inches +/- a little). Most of the antennas used for R/C radio are not 1/4 wave length, or any other 'common' electrical length, but ~much~ shorter. (Ever see a 9 foot antenna on an R/C boat?:))
None of that has particular electrical significance for receivers, but a huge significance for transmitters! Receivers just ain't as 'picky' as transmitters are, sort of. So, the 2.4 Ghz stuff is really the closest thing to "scale" for models as it gets, and that makes getting into learning all that radio stuff sort of important IF you're gonna start 'messing' with unusual lengths of antennas (not stock).
The simplest way of looking at this is that the longer the receiving antenna, the better the range, to some ridiculous point. R/C range is limited to start with, so shortening a recieving antenna isn't the best idea in the world (at least not much). Making it more longer is more better, sort of. It shouldn't harm the receiver if an antenna is made longer/shorter. It definitely can harm/help the usable range.
If/when you start playing with the connecting cable (coax), you have started playing a very "iffy" game. That cable has certain characteristics that are used in the circuit. If you can keep those characteristics the same as the original ones, you'll do fine. If you can't, you come out on the short end of that proverbial stick (and it won't be the 'clean' end!). I really wouldn't recommend that unless you like to experiment a lot.

And having bored you to tears, I'll quit.
- 'Doc
(Certified radio nut)


Can't resist!
And for the other 'radio nuts' out there... If you ain't got Kenwood, you got squat!

[Julez]

Changing antenna length:

http://christian-hanke.blogspot.com/2008/03/change-length-of-futaba-antenna.html

[Reckless]

thanks again guys :D

and LtDoc didn't bore me at all... I got relatively serious in dabbling with electronics and CB/sideband radio... so I did understand all the wavelength and antenna length stuff

before I start cutting things up I'll atleast just give it a go "normal' like and just see what happens... it's a dynamic diver so if it goes dead stick it should just come to the surface ... if something 'bad' happens the water is only 4-5 ft deep and nearly crystal clear.. so not much of a stretch to go for a swim and retrieve it