interested in loaded antennas

[jstevens]

I have been eyeing the loaded antennas that are for sale, and wanted to put one in my helicopters. They look pretty simple to make and I wondered if anyone knew of the size of capacitor that is used in making them for the 72mhz bands?

[steve lewin]

Err...there's not usually any capacitor in a loaded antenna.

Try http://www.uoguelph.ca/~antoon/gadgets/flywire.htm

Steve

[jstevens]

What are these coils that the website is talking about? 1.5 micro-henry? I saw some loaded antennas this weekent at the columbus indoor fly-in and they looked like resistors. was hard to tell exactly under the shrink wrap though.

[steve lewin]

They are 1.5 uH inductors. They do indeed look like resistors but they are not resistors or capacitors, they are inductors. They're nowhere near as easy to find as Rs and Cs but try Digikey or somewhere like that.

Steve

[HitTheDeck]

Any body know what size inductor I would need for 35mhz over here in europe??

[Robbie d]

i gave up with the loaded idea. i grabbed some magnet wire and wrapped half a wavelength of wire around a plastic tube
i used fishing line as a spacer between windings of the wire. the antenna came out about 4" long

[BMatthews]

Inductors are not anything magical. They look like resistors but in fact what they are is just a coil of wire. To help them stay small the coil is often wrapped around a small bit of ferrite or other core material. Then to protect the structure they pot them in plastic just like resistors.

If you can find a HAM radio site or other electronics place there's often patterns there for winding your own air core inductors using simple varnished solid wire.

But if you know what you're doing it'll probably come out similar to Robbie D's method. I'm not sure about the 1/2 wavelength though. Our normal whips are 1/4 wave and loaded wire lengths are sized to take into account the inductance and inter turn capacitance of the windings. But hey, if Robbie hasn't crashed yet then it's good, right?

[KillerWatt]

Well...... one could use a capacitor in the antenna system, if determined to do so...... you'dd just have to use about twice as much antenna length (about 7 feet long) as normally supplied with the receiver, but who would want to do that !!!!.......... kw

[Robbie d]

my friend has testflown my 1/2 wave antenna on a gws 4 channel receiver with no range problems. i have also done a 1/4 wave antenna but decided that 1/2 wave in theory should be better

[steve lewin]

Actually the optimum antenna length for an RC receiver is the length it was designed with. RXs already have some internal loading so messing with the length, either by increasing it or decreasing it, can reduce the range. This is not a case of "bigger is better" ;).

BTW isn't 1/2 wave length on 36MHz an awful a lot of wire ? Around 13ft.

Steve

[Robbie d]

it was 4 metres of wire, yeah i guess 13 feet. but wound around a 1/2" former, it became 4" or so