433 MHz Antenna?

[brodin]

I am constructing a device that has 3 PIC:s on the PCB and a lot of other components. I also have a 433 MHz AM radiotransmitter at 10mW onboard. I am thinking about the antenna for the transmitter. Should i connect a piece of wire in the box, or should i make leads on the board and use as an antenna(would that work)?

How long should the antenna be?

 

[Nigel Goodwin]

I am constructing a device that has 3 PIC:s on the PCB and a lot of other components. I also have a 433 MHz AM radiotransmitter at 10mW onboard. I am thinking about the antenna for the transmitter. Should i connect a piece of wire in the box, or should i make leads on the board and use as an antenna(would that work)?

How long should the antenna be?

These devices are usually licence free, part of the licence free conditions concern the aerial - the datasheet for the transmitter should give details of permitted aerial designs - or perhaps on a separate datasheet, but those I've seen all include it on the main datasheet.

 

[kitedude]

ok heres the the calculation your looking for.

say signal is 433mhz
433*10^6/3*10^8 = 1.4333.
1.4333./4 = .36
which would mean the the optimal antenna size is 36cm

 

[Russlk]

Mouser sells antennas for 433 mHz. www.mouser.com

 

[kinjalgp]

ok heres the the calculation your looking for.

say signal is 433mhz
433*10^6/3*10^8 = 1.4333.
1.4333./4 = .36
which would mean the the optimal antenna size is 36cm

Ok, here is a bit of explanation to understand what 'kitedude' has done.

Lambda (Wavelength) = Signal Frequency / Speed of light
Lambda = 433*10^6/3*10^8 meters
Lambda = 1.4333 meters

Minimum length of antenna for effective transmission should be atleast Lambda/4
Length = 1.4333/4 = .36 meters = 36 cm

 

[brodin]

Okay, thanks for the good explanations!

So 36 cm would be ok. But what about the area of the antenna?

Is 36 the optimate length or will the tranmitter be better if there is a longer antenna?

 

[Nigel Goodwin]

Okay, thanks for the good explanations!

So 36 cm would be ok. But what about the area of the antenna?

Is 36 the optimate length or will the tranmitter be better if there is a longer antenna?

An aerial is tuned to a specific frequency, making it longer will alter the tuning and make it worse - there are various ways of doing it, but simply 'making it longer' isn't one of them.

As I also mentioned earlier, please consult the datasheet to check your legal obligations as regards the aerial choices.

 

[brodin]

I have look in the datasheet that i got from my dealer. But it is no real data sheet. Look at it. Could it be simplier?

 

[Nigel Goodwin]

I have look in the datasheet that i got from my dealer. But it is no real data sheet. Look at it. Could it be simplier?

I don't think your attachment made it :lol:

Here's a clip from an RFSolutions datasheet.

I have seen others which give a PCB layout for an aerial.

 

[stevez]

The behavior of an antenna at that frequency will be profoundly affected by many things including the proximity to other conductors or non-transparent (to RF) materials. Waving your hand past it will affect it. A quarter wave length of wire is a place to start but I think you'll have to experiment - keeping in mind the legal issues already mentioned. I'd argue that others have experimented and found antenna configurations that work well in a given situation or environment. What you'll likely find is that just about anything will radiate - and that your situation won't allow the ideal antenna.

For what it's worth - amateur radio operators have a band at or near that frequency. They do make "rubber duck" antennas for that band - a very short stubby antenna with a BNC, SMA or other connector. They are far from ideal, as antennas go, but are likely to function as well as can be expected given an unpredictable near-field environment. They might offer some directivity or gain but it would seem no more than a well tuned dipole or ground plane. I'd use one of these as a place to start.

 

[brodin]

Thanks everyone for you information.

Lambda (Wavelength) = Signal Frequency / Speed of light
Lambda = 433*10^6/3*10^8 meters
Lambda = 1.4333 meters

Minimum length of antenna for effective transmission should be atleast Lambda/4
Length = 1.4333/4 = .36 meters = 36 cm

Will this calculation work for receiver antennas to?

 

[Nigel Goodwin]

Will this calculation work for receiver antennas to?

There's no difference between them, apart from a badly tuned receive aerial causes poor reception, and a badly tuned transmit aerial causes the transmitter to die! - unless the transmitter is very low power, or designed to be particularly robust..

 

[kinjalgp]

Will this calculation work for receiver antennas to?

Yes, according to "Reciprocity" theorem of antenna theory, whatever is applicable to transmitting antenna apples to receiving antenna also.

 

[jfunkie]

Hi,

How about a microstrip antenna? Is this possible?

 

[Spectacular Butter]

ok heres the the calculation your looking for.

say signal is 433mhz
433*10^6/3*10^8 = 1.4333.
1.4333./4 = .36
which would mean the the optimal antenna size is 36cm

Ok, here is a bit of explanation to understand what 'kitedude' has done.

Lambda (Wavelength) = Signal Frequency / Speed of light
Lambda = 433*10^6/3*10^8 meters
Lambda = 1.4333 meters

Minimum length of antenna for effective transmission should be atleast Lambda/4
Length = 1.4333/4 = .36 meters = 36 cm

Where do you get this calculation from? Is there any reference about this calculation on the web?

 

[Russlk]

Hi,

How about a microstrip antenna? Is this possible?

Microstrip is a way of making a transmission line on PC board. The objective is to not have it transmit!

 

[mstechca]

For 433 Mhz, a short antenna should work. Maybe stick a variable capacitor in series with the antenna.

As far as I know, a capacitor in series with an antenna electrically makes a reduced size antenna, and an inductor in series with an antenns electrically makes an extended size antenna. Correct me if I'm wrong.

 

[Russlk]

A capacitor in series with a physically long antenna will make it electrically shorter. An inductor in series with a physically short antenna will make it electrically longer. The inductor has to be at the high current end of the antenna or it will not be effective.

 

[Nigel Goodwin]

A capacitor in series with a physically long antenna will make it electrically shorter. An inductor in series with a physically short antenna will make it electrically longer. The inductor has to be at the high current end of the antenna or it will not be effective.

Perhaps I'd better explain this further? - doing this doesn't make it as good as a proper length aerial!, all it does is make it appear the correct impedance to the transmitter. The aerial being the wrong length will always perform worse than one the correct size - loading it in this way is a 'bodge' so you can use an unsuitable aerial (though at a lower efficiency).

 

[saunj]

ok heres the the calculation your looking for.

say signal is 433mhz
433*10^6/3*10^8 = 1.4333.
1.4333./4 = .36
which would mean the the optimal antenna size is 36cm

Your equation is upside-down. 1/4 wave antenna at 433 MHZ is 6.8 inches