Hi all,

Please i need advice regarding walky talky that work on a 433Mhz, 0.5w, my question is witch type of antenna should i use to get more coverage area, or if i can build a small amplifier. i saw some on the net and i'm really confused, since i have no experience in RF.

Regards,
:delta: fOLIA :delta:

Originally Posted by folia

Hi all,

Please i need advice regarding walky talky that work on a 433Mhz, 0.5w, my question is witch type of antenna should i use to get more coverage area, or if i can build a small amplifier. i saw some on the net and i'm really confused, since i have no experience in RF.

Regards,
:delta: fOLIA :delta:

A quarter wave vertical with a ground plane and four radials, placed as high up as you can make it, should be worth a couble of dB. Check out the ARRL Radio Amateurs Handbook or the Antenna Book for construction details and parts lists.

I suspect that without a license any kind of RF amplifier would make your rig illegal.

Code:

3e8 (speed of light) / 433e6 (frequency) = .6928 m

This is the 70 cm Band

A quarter wavelength is 0.1732 m = 6.82 inches

I agree with Papabravo; however, to add a little ... does your antenna need to be omnidirectional or can you get away with it being unidirectional? If you can easily adjust the antenna or if you can use a motorized rotator (or simply if it can be fixed), you can get yourself a couple more dB if you go with a yagi, log-periodic array, or some other sort of directional beam. The nice thing is that the 70cm band is such a nice manageable wavelength so even a high gain directional antenna does not have to be very large. Remember that even a full wavelength at this frequency is only 70 cm. To make it even more convenient, if your transmitter is at a fixed frequency and does not need to work over a range of frequencies, you can tune the antenna to the exact frequency of interest, eliminating some other problems such as poor VSWR at the band extremities.

The ARRL Handbook and Antenna books are the best reference that I can think of as well. There are also some good publications from the Radio Society of Great Britain.

I don't know your application or what you're doing with this so I'll try not to be a pain (you may have an amateur radio license for all I know) - but I just have to warn you that you're right in the middle of the 70cm/440 MHz ham radio band which extends form 420MHz to 450MHz (in the US at least). Even transmitting at 0.5W at 433 MHz is illegal in many (if not all) countries without an applicable amateur radio license. In the United States for example, the minimum license would be the Technician class Amateur Radio license; however, most countries have some form of amateur radio license for this band and at least in the US they'll enforce it if someone starts complaining. Again, I don't know what you're doing with this, but if you don't have a license, I would get one and you can transmit till your heart's content - and with an amplifier up to 1500 Watts if it's necessary - as a hobby of course.

Good luck

Hi all,
First I would like to thank you all for your reply and wish all forum members a happy New Year.
About my application, simply I have 4 walky talky from a good brand that you can use it without a licence and they mention that it will cover around 5km, I’m using those device in a working area that there some geographical obstacle, and I was wondering if I will use antenna with a tower, it can do a good job to cover a bigger area.
Regarding the antenna is there’s any description how to build if that possible like good material…
Regards,
fOLIA

Thanks a lot, i think it's better to have lisence ad to get more powerfull device.
Regards,
folia