how do you make a "loaded aerial"?

[betty.k]

a loaded antenna is an antenna that looks electronically large while being physically small

eg: a 27 mhz aerial should be around 11m to match the frequency. 1/4 of this is an accepted length.
but that still leaves you needing an aerial over 2m (like 6ft).
a 27mhz loaded antenna would be only a few inches in length physically,but electronically would look like an 11m one.

i wanna make one for my heli which is 35mhz.

when i searched on google all i get is links to sales for built ones, i’m hoping i can make my own with what i got.

so can i? or will i need to buy a loading coil and use an oscilliscope (sp?)

[merc-blue]

Ive got a spare Azzar one if you want it,

i had found a tute online for one ill see if i can find it

[trash]

Basically betty, it isn’t really that hard to do.
In your case crunching numbers isn’t going to help a lot, but trial and error will work well for you.

Loaded antennas come in a couple of forms, bottom, top and center loaded.
I’ll skip the complex and boring information on each type.

A good place to start is with an old CB antenna. Obviously they are tuned to 27MHz and are usually top loaded. Unwind the wire, cut the antenna short and rewind the wire on in the new position basically trying to mimmic what you started with on a smaller scale.

I wrote a nice tutorial on testing transmission lines and antennas.
http://www.austech.info/showthread.php?p=1047955#post1047955
the bottom half deals with antennas.

Ideally you’d use a 27MHz SWR (it’ll work for 35MHz) and a 35MHz oscillator or transmitter with enough power to drive the SWR to be able to test the antenna. I fear your RC transmitter will only be a couple of hundred milliwatts and not really enough to drive the meter fully.

If you’re talking about an RX antenna for the chopper. Don’t bother… the piece of wire currently in use will suffice.

Seeing that you’re taking an interest in electronics and radio. Might I suggest that you or anybody else interested in radio and electronics consider the new ham radio foundation licence. http://www.wia.org.au It’s very easy to get these days. No morse code and the test is 20 questions easy multiple guess. Easier than getting your L’s for a car.

[betty.k]

coolness, thanks for the info and links!

i’m not planning on getting right into radio stuff, i just look for stuff on a need to know basis.

the aerial i was going to upgrade was the rx aerial. i found out that 1/4 wavelength aerial using cat5 type wire only weighs 2.6g so i just went with that.

i also popped the question at my local rc plane/kite shop (hawthorn hobbies). the guy then explained how he does lots of stunt and precision flying and said he wouldn’t touch a loaded aerial with a 10 ft stick!
so i’ll stick with the 1/4 wave rx aerial. my heli is like an iwaver (colco) so if i want better reception i’ll have to spend more cash :8ball:

[merc-blue]

only 2.6g? what did you calculate your wavelength as?
i got wavelength at 36mhz to be aprox 8.3276 meters so a quater of this would be 2.08 meters i cant see 2 meters of thats qire being only 2.6g

[betty.k]

yup, that’s what i thought too until i threw it on the scales. i based my calculations on 35mhz so 1/4 wave is 2.14m long :8ball:

[klims]

hey guys.

i’ve tried making myself a few “loaded” aerials for my mini z. so far the results are good. what i did was go into supercheap and check out some of their 27MHz aerials for the CB’s. there were some bottom loaded, some mid loaded and to my amazement there were some that were both! anyone know whats up with that?! anywho i went into my local dick smith and bought some enamled wire and rigged one up.

im not sure if its just the larger amount of wire, but i was getting great results with 1/20 wavelength bottom loaded. 1/10 was far too long. my steering no longer jitters, and my z doesnt go out of control and tear itself to bits! it seems to be a great setup. im still playing around with the lengths and the diameter of the coils so i guess testing is not over

has anyone tried anything different or got different/ better results? i have heard that there is also an optimum diameter for the coils to be. anyone know how that works?

[klims]

hey guys.

i’ve tried making myself a few “loaded” aerials for my mini z. so far the results are good. what i did was go into supercheap and check out some of their 27MHz aerials for the CB’s. there were some bottom loaded, some mid loaded and to my amazement there were some that were both! anyone know whats up with that?! anywho i went into my local dick smith and bought some enamled wire and rigged one up.

im not sure if its just the larger amount of wire, but i was getting great results with 1/20 wavelength bottom loaded. 1/10 was far too long. my steering no longer jitters, and my z doesnt go out of control and tear itself to bits! it seems to be a great setup. im still playing around with the lengths and the diameter of the coils so i guess testing is not over

has anyone tried anything different or got different/ better results? i have heard that there is also an optimum diameter for the coils to be. anyone know how that works?

[Ogier]

I’m not sure what these look like (I’ll read the links at the top of this thread soon) but one of my colleagues just installed a springy antenna on his iWaver and it eliminated his tyre shake! We were both surprised by this.

my stock iWaver with no antenna attached has operated in an underground car park at approx a 100m range. It might have been a little bit glitchy at that distance, but I did drive it back. The standard short antenna wire was just pointing upwards and I didn’t have a body on it. It was so far away it was very hard to see which way it was pointing.

I guess I’m a bit puzzled – maybe some boards & transmitters are more accurately in tune with each other?

[klims]

yes they are springy antennas with the “spring” at either the bottom, top of middle.

underground car parks are not a very good place to be testing signal strength. the concrete walls block out a lot of noise and also help in reflecting the transmittion around, so both result in much better reception

[betty.k]

i’ve since found some links that answered my initial questions.

http://www.uoguelph.ca/~antoon/gadgets/flywire.htm
http://www.iroquois.free-online.co.uk/aerial.htm

as i don’t have any inductors handy i’ll try making my own with the enamelled copper wire first. if that won’t work i’ll head down to jaycar and buy some real ones :8ball:

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