433Mhz RF antenna

Hi,

I am using the FS1000A to transmit and receive RF. It works fine at 10m or less but longer than that I cannot receive any signal.

I see that there is an "antenna" area in both chips (transmitter and receiver) and I read a lot in Google how to make this antenna but got no good answer.

How can I create this antenna? Can I use a copper wire, remove the plastic and weld it in the antenna area in the chips? Should I twist the antenna n times?

Hope you can help me get my signal further! :slight_smile:

17cm antenna wire. I have used 30AWG wirewrap wire. Striip the end and solder it to the antenna pad.

Make the wire 1/4 wave long. You do not need to strip the insulation.

Circle? It's only 6.7 inches long.
For my use in a remote control, the transmitter just followed two inner sides of the box.
See the white wire on right hand side & bottom.

The receive box was larger, antenna just lays loose inside with the far end not touching anything active. Can see the Rx card in the middle control board, can't really see the antenna wire.

You don't have to twist it or circle it to receive from all directions. Just point it straight up or straight down.

A quarter wave antenna should be at 90 degrees to a ground plane ideally. Bringing it
closer to metal will detune it significantly (more of an issue for transmit than receive).
Unless you have the setup to measure signal strength properly just leave it straight. Your
quadcopter frame isn't an ideal ground plane in the first place so the antenna sidelobes
are anyone's guess... Given you're likely to have line-of-sight path I wouldn't worry too much.

Agreed with MarkT.

An antenna may be wound into an inductor in order to shorten it when space is at a premium. But it must be tuned, then, and space is -not- at a premium. Did you look at the antenna pattern? That was for a 1/4 wave over an infinite ground. On a quad copter, it acts a bit more like a vertical 1/2 wave dipole and so the pattern looks like a very fat donut.

So yes, it will pick up below the craft. I apologize for not being clearer about that.

A quarter wavelength is the optimum length, so increasing or decreasing the length will decrease the range.

Unless of course your adjustment compensates for the non-ideal ground plane. 8^)

gilperon:
The antenna of the receiver is not a straight wire, it is a wire that is twisted several times to have coils. Do you think I should do that?

No.

The longer the antenna is, the more efficiently it works. Coiling it is to make it fit into a smaller space, but it markedly reduces the gain factor. It literally "picks up" or collects less of the available radio waves.

And on an aircraft, a vertical antenna with horizontal radiation pattern is a good thing as you need the least gain when it is directly above as by definition, when it is directly above, it is also the closest it will be.

Do some reading

OK, there are two aspects here.

One is that the gain of the antenna - its effectiveness for transmitting and receiving - is proportional to the length of the antenna.

The other - and important one - is that to fully achieve this gain, the antenna must be resonant - it must be tuned to the frequency in use.

Those short coiled antennas are (should be) tuned by the inductance of the coiling. A quarter wave antenna is the resonant length, will generally be straight. If you use longer than a quarter wave, it can be tuned with a series capacitor (generally a variable capacitor to allow it to be adjusted). When the length is a half wave, it will be again resonant and require no tuning, but it will have a very high impedance at the end which is inconvenient to connect to your transmitter/ receiver.

Paul__B:
One is that the gain of the antenna - its effectiveness for transmitting and receiving - is proportional to the length of the antenna.

That is only true for an antenna much shorter than 1/4 wave. As has already been stated 1/4 wave will be best, any longer and the performance degrades.

If you need more range you need to use a directional antenna such as a Yagi but that will probably radiate more than the legal field strength for that frequency band.

Russell.

russellz:
That is only true for an antenna much shorter than 1/4 wave. As has already been stated 1/4 wave will be best, any longer and the performance degrades.

Not true or we would not be using 5/8 antennae on our cars.

The performance is degraded only if the antenna is not tuned. That is what I explained previously. Tuning an antenna longer than a quarter wave (less than a half wave) is particularly easy as capacitors are cheap.

Paul__B:
Those short coiled antennas are (should be) tuned by the inductance of the coiling. A quarter wave antenna is the resonant length, will generally be straight. If you use longer than a quarter wave, it can be tuned with a series capacitor (generally a variable capacitor to allow it to be adjusted). When the length is a half wave, it will be again resonant and require no tuning, but it will have a very high impedance at the end which is inconvenient to connect to your transmitter/ receiver.

That's a very interesting post. Any article you'd advise us to read regarding the theory behind?

Short coiled antennas are called helicals.
They are commonly used in small devices where space is a premium as a helical is physically smaller than the more common 1/4 wave antenna .
The theory behind them is here.

mauried:
The theory behind them is here.

Well, not quite!

That article is in regard to an entirely different type of antenna - which is in fact, many wavelengths long.

The theory of short antennas is relatively simple. A short antenna essentially appears as a capacitive reactance, and must therefore be tuned with an inductance in series. An inductance is of course, a coil, and for most antennas, it is an "air-cored" coil (or at least, wound on an insulating "former"). The coil may be placed at the base of the antenna or part-way along (which improves the efficiency). It is then frequently practical to make the whole of the antenna, a coil.

And on an aircraft, a vertical antenna with horizontal radiation pattern is a good thing as you need the least gain when it is directly above as by definition, when it is directly above, it is also the closest it will be.

On my quadcopter I let the antenna dangle below it and gravity keeps it straight.

Heres another article on helicals that may explain them better.
http://scholar.lib.vt.edu/theses/available/etd-02102000-19330046/unrestricted/07chapter2.PDF
Helical antennas are not resonant and operate as a broadband antenna with normally an octave or more bandwidth.
In normal mode , the antenna is not tuned and needs no loading.
Heres a picture of a vary small helical antenna as used on a walkie talkie radio.

Unfortunately you continue to confuse two quite different forms of "helical" antenna.

The ones we are talking about are called "normal mode" and from the reference you quote,

Because of its small size compared to the wavelength, the normal-mode helix has low efficiency and narrow bandwidth.

It is by no means "broadband" and must in fact be very carefully tuned for decent performance.