Antenna design for RF modules.

[myfaithnka]

Hi all,

I am hobbyist and a newbie,Now I am trying a wireless project.

I am using TX 433-RX 433 modules due to the low cost and availability.The modules can work at a distance of 500 meters.

The modules have working frequency is from 300 to 434 MHz


Now I need to design and antenna for them,to achieve a distance atleast a 350+.

I came to know that Helical antenna working in Normal mode has gain more than long wire antennas(please suggest if better Ideas are there),But a practical approach towards this design was hard to find.

Friends please help me.

Nithin Kamal A
myfaithnka@gmail.com

 

[goldsmith]

Hey Buddy!
Hi
Why you don't use yagi antenna? it has direct pattern and i think it is ideal for this range of frequency. and it's designing is very simple.
See below links , please:
Free Yagi Antenna Designs for Ham Radio
**broken link removed**
http://0x7.ch/text/yagi-slides.pdf
http://www.qsl.net/yu1aw/Misc/yagi_sens_pract.pdf
http://wireless.ictp.it/handbook/C4.pdf
http://www.wa5vjb.com/yagi-pdf/cheapyagi.pdf
http://www.techlearner.com/Apps/AntennaDes.pdf
Best Wishes
Goldsmith

 

[FvM]

I came to know that Helical antenna working in Normal mode has gain more than long wire antennas

Sounds unlikely. Normal mode implies an antenna shorter than a lamda/4 monopole and thus more omnidirectinal pattern rspectively lower gain. If you don't care for legal restrictions (antenna gain limitation), a multi element yagi is the ultimative solution.

 

[myfaithnka]

Dear gold smith and fvm,

Thank you,but the problem i face is that the antenna must be highly mobile.

Thats why i choose helix and whips...

I had once tried yagis,what to say...replaces aspirin sometimes...

 

[FvM]

the antenna must be highly mobile

Although there may be doubts what a highly mobile antenna exactly means, if we understand it as small antenna, a lambda/4 (17 cm) whip will be a usual trade-off between size and performance. A sufficient instrument size as "counter balance" respectively ground plane is required however. A smaller antenna must be expected to reduce the range.

 

[myfaithnka]

fvm,

it will be possible,please tell me how to design them in practical case.

I am starting to believe whip is better than helix...

 

[FvM]

There isn't much to design. One border case is the λ/4 rod over an infinite ground plane, it has a nominal impedance of 40 ohm, the other a λ/2 dipole with 73 ohm impedance. In an more exact analysis, there is a certain dependence of impedance and optimal length on rod diameter. In most cases, one uses a thick wire or thin tube, that can be still assumed as ideal wire in analysis.

A real mobile instrument with monopole antenna and sufficient ground plane size will range somewhere between both sketched border cases and most likely show an additional reactive impedance part depending on the ground plane size. Ideally, empirical impedance matching would be applied. As the antenna impedance is at least near to 50 ohms transceiver impedance, just connecting the antenna without individual matching network is often the obvious solution.

 

[myfaithnka]

fvm,

thanks alot.

can use copper ?

in case of an impedance matching...how could i find the output resistance of the tx 433-rx 433 modules.

 

[FvM]

Yes copper is O.K. and often used, also brass, sometimes nickel plated. Aluminium is fine as well, if you have a suitable way to connect it.

433 MHz modules have mostly 50 ohm impedance.

 

[myfaithnka]

that means if the wire cant provide 50 ohm,we need to add it within the circuit,right ?