aerial questions

[betty.k]

i was wondering if there were special considerations regarding aerial material, shape and length. does a coily aerial affect reception? is there an optimum position on the vehicle?:8ball:

[trash]

Generally for your BCG car, it doesn’t really matter how long your antenna is.

Antenna Theory Time. 🙂

There is a very important number everybody should know. 3 x 10^8 ! (300 Million). It’s also known as “the speed of light” (in metres per second).

It is the “C” in E=mc^2, but I don’t think we need to go that far 🙂

We use this number to work out the ‘wavelength’ of a particular radio frequency.

The formula is L= C/F
C= 3 x 10^8
F= Frequency in Hertz (27MHz = 27000000 Hz)
L= Wavelength (in metres)

Example:
[3×10^8]/[27×10^6]=11.11 metres.

Antennas work best a specific lengths.
Usually these are 1/4, 1/2, 3/4 and 5/8ths of a wavelength.

Stick with 1/4, it is simple and the smallest.
11.11 / 4 = 2.78 Metres.

So the best length of antenna to use is 2.78 metres long. Not very practical ?

Loading coils help make antennas look electrically longer or shorter than they really are. But for antennas so drastically short of their ideal length, it doesn’t help much.

You may of course care to try experimenting with other types of antennas like a loop antenna.

[barto_85]

I think ph2t gets good results using guitar string as the antenna.

[twizm]

itd be good if my brother ever broke his guitar strings, but he doesnt. and my bass strings are too fat to use. guitar/bass strings arent cheap either. im not sure if you can buy individual strings anymore or even if you could.

[trash]

Go the cat5 !
Hmmm… I take it you don’t mean the nylon strings ? 🙂

Coathanga – Maori word for car antenna.

[Super Max Power]

What if you used a guitar string in the shape of Australia?

[betty.k]

i like that idea super max!:D
so what about the metal? is copper best?
and how do i go about making a loop aerial?:8ball:

[twizm]

gold is supposed to be the best metal for transferring signal isnt it? all my A/V plugs/sockets, headphones and leads are gold tipped, or at least gold coated.

[Super Max Power]

I was just speaking to my flat mate (who is currently doing a PhD in micro electronics – specifically antenna design). I figured he would be a good guy to ask.

He reckons that twisting, bending, looping, changing metal and lengthening antennas in micro cars would have little or no effect.

But, after a lengthy discussion (or argument)he has conceded that for a micro car application – a longer antenna made with a high conductive coating will produce a better than stock antenna. A point of note – an antennas signal is carried by the outside of the antenna material i.e. a copper coated wire is better than a nickel coated one.

An antenna in the shape of Australia would have no effect. I am deeply cut.

[betty.k]

hmm, interesting. i was thinking of using enamelled copper wire and now i probably will. it will also be good as it will look ‘anodized’:8ball:

[micro_Amps]

SMP, I love your aerial idea, lol. A little Aussie humour there.
Your flatmate is correct, its called the ‘skin effect’ , electrons prefer to travel on the outside edge or ‘skin’ of the conductor.
The biggest difference that I have seen in terms of improving the range of the BCGs is the longer aerial. The higher the aerial reaches off the floor, the better the range. To prove this just put something on your controller so a button stays pressed, pick your car up of the floor and walk away with it. You will see just how far these cars can go.
The guitar strings work extremely well because they are light and thin, better in fact than the Cat5 wire which is heavier.
Having a telescopic aerial on the Tx improves range as well because the tip of the aerial stays higher off the floor. The droopy wire aerial doesnt do alot to for the range.
:)uA

[ph2t]

One word, guitar string. You can’t go wrong. Everyone can argue theory till the cows come home. At the end of the day
cause-and-effect is the best way of finding what is best.

Here’s some info I posted on another forum:

Guitar String, hell yeah I’m sure…It’s the best antenna in my mind…

1) The antenna is tensile, you can hit obstacles and not worry about it bending, it always retains it’s shape.

2) The antenna is always straight, at 90 degress to the ground. The more right-angled the antenna is to the ground the better reception you get and therefore a longer range is achieved.

3) Looks better, you can hardly see it.

4) With this antenna I’ve achieved an avg 11 meters indoors and over 20 meters outside. (that’s 33′ and 60′ respectively). This includes removing the crip-cap from the car(if it’s there) and tuning the variable inductor on the RX pcb.

5) It’s lighter than CAT5, therefore the moments(interia on the antenna) generated by this length of antenna is less than a CAT5 antenna of same length. This means better balance across the four wheels.

Below is a tutorial I wrote up for a ZipZap SE, the principle is the same though.

Pretty much all you need to do is goto a music store and ask for a Number 9 electric guitar string. If they ask more questions just ask for the “bottom E” the lightest string on the electric guitar.

You need to pull apart the zzse and remove the rear plastic “knob” that holds the pcb down. You will also need to remove the front plastic facia that covers the pcb there as well.

Remove the old antenna and notice where the solder point is. What you want to do is “pre-bend” the string to follow the path of the original yellow (mine was yellow) antenna. See below:

Before bending I put some plastic wire sheath from some hobby wire over the string. I dip the end of the string is a tiny bit of superglue and then feed the wire into the sheath. This allows the plastic cover to stick to the wire and then you can bend it to the shape you need as shown in the picture above.

The following pic gives you an idea of the length, approx 12cm.

Make sure you put a protective cover over the end of the string or at least curl the end around to protect your eyes!

The final pic below shows you how I ran the antenna though the hole of the plastic holder knob thingy……

Hope this works for you. This mod increased the range of my zzse bigtime!

ph2t.

[trash]

Gold isn’t the most conductive metal, it’s actually Silver. Gold is used because it’s more inert than silver, and cheaper than platinum.

The skin effect is correct, but it actually has very little to do with antennas, it’s more to do with transmission lines.
Though it can be said, that the thicker the antenna’s elements, the more broader its bandwidth.

It doesn’t matter what you make your antennas out of. It can be ANYTHING ! I’ve made antennas out of fences, power lines, even trees and people !
(though it is common knowledge a human being makes the best TV antenna). I even have an antenna that is plastic ! (it requires some explaining).

So it doesn’t matter what sort of metal you use in this case. There is something that I have overlooked. It’s a thing called ‘velocity factor’
it has to do with the speed at which electrons travel in wires. In free space C=3×10^8, in a metal wire it is slower.

I’m not sure that such a short antenna has a flat radiation pattern, so keeping it a 90 deg to the floor may not make any difference. Short antennas are rather unpredictable so the only way to find out is test them.
The guitar string antenna looks pretty cool.

The coil antenna, you just take a long length of copper enamel wire and make a loop big enough that will fit inside the chassis. 10 turns is usually enough and then you leave a tail for the antenna. I haven’t experimented much with it, so it’s new ground. 🙂

[betty.k]

my aren’t we a bunch of boffins! good work guys. i wasn’t really asking specifically about bit aerials, but i got what i wanted anyway. whenever i’ve wanted an aerial in the past i’ve just stretched out a spring, for most of the reasons ph2t uses guitar strings. btw you can use bass guitar strings, you just have to use some pliers to grab the end of the outer coil and unwind it by pulling it off. the inner wire is a bit thick, but the squiggly outer wire is perfect:8ball:

[betty.k]

just thought of something else i wanted to know. just say i wanted to run a rc vehicle with 2 pcb’s on different frequencies (simple way to ad extra channels). can the rx’s and tx’s run on the same aerials? or would they need to run on separate ones.:8ball:

[ph2t]

I would say seperate antennas, especially for the TX’s. But hey the best thing to do is just try it and see what happens…..

ph2t.

[trash]

I don’t see any reason why they couldn’t share an antenna on the RX. You might need to do something if the local oscilators interfere.

[Author]

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