Building a wireless remote at 433Mhz 1

[DotComSurvivor]

Most of the designs I see use quarter wave loop antennas.
Since these designs are very inefficient in this frequency range, high Q and so difficult to match, I was wondering if anyone had experience building/employing an alternative antenna type for this frequency band?

Look forward to any input on this one

 

[VEBill]

A high Q antenna is typically efficient (low loss).

 

[DRWeig]

DotComSurvivor,

How far do you need to transmit, through what sort of obstructions (if any), and how much power are you proposing?

I'm not a radio expert, but there are a number of them right down the hall from me and I'd be happy to ask.

Old Dave

 

[DotComSurvivor]

Hi Dr Weig,

Thanks for your post. I have a 5dbm transmitter and and hope to go 200ft. The receive sensitivity is ~-98dbm.

Thanks for any feedback.

 

[DotComSurvivor]

Thanks VE1Bill,

I guess the loop antenna has poor efficiency in this case (at 433Mhz) because the radiation resistance will be so much less than the skin effect resistance, because of the small loop size.

 

[SolderingGunslinger]

If you really need to use a loop antenna, consider using a full wave loop (Cubical Quad antenna driven element). Make it from 1/4-Inch (25mm) refrigeration tubing and silver plate it.

One other thing to remember, 433 MHz is smack-dab in the middle of the 70 cm Amateur band in many parts of the world. Hams guard their frequencies with the ferocity of a mother bear protecting her cubs. Even though there are some unlicensed devices which use parts of the 70 cm band, the manufacturers keep the radiated power levels down, often by using inefficient antenna designs. Increase the radiated signal and you might incur the wrath of the local Hams and the government offices which have jurisdiction over communications.

If you are a licensed Ham, be sure to identify your transmissions.

Good Luck and have fun!

I remain,

The Ol’ SGS

 

[VEBill]

A good antenna is often considered to be good because it provides some gain. Gain implies directionality. Directionality may not be a Good Thing for remote controls unless you're prepared to aim it. It depends on the application.

Antennas that are nearly isotropic are often otherwise horrible.

 

[DRWeig]

DotComSurvivor:

The word from the radio guys down the hall is that the 1/4 wave loop is considered the "best overall" for compact designs when sensitivity, cost, and the difficulty of matching are considered. However, there are lots of alternatives. We do lots of 918 MHz stuff here, but our radios are kinda sophisticated and the antenna-matching process is automated.

Your 433 MHz will give good penetration, and you should get your 200 feet no problem.

Suggest you have a look at this resource:

http://www.techlearner.com/Apps/AntennasLowP.pdf

Let us know what you decide to do!

Old Dave