Antenna woes

[Mark Lazarides]

Hello all. I'm using RF communication in a project i'm working on at the moment. I haven't used RF before (normally i mess about with IR). I've come across a trivial problem though.

I'm using a radio transciever unit that porvides an RF trans/rec pin, with two ground pinseither side for connection to the antenna. The antennas I've chosen are whip (for the non space critical side) and stubby helical (for the space critical side).

Both have M4 style thread connectors, but that appears to be it. Could someone then confirm for me that this needs to be connected to the RF pin of mr transceiever module and nothing else? I can't see where I could ground it? Thanks for any suggestions.

 

[Nigel Goodwin]

Hello all. I'm using RF communication in a project i'm working on at the moment. I haven't used RF before (normally i mess about with IR). I've come across a trivial problem though.

I'm using a radio transciever unit that porvides an RF trans/rec pin, with two ground pinseither side for connection to the antenna. The antennas I've chosen are whip (for the non space critical side) and stubby helical (for the space critical side).

Both have M4 style thread connectors, but that appears to be it. Could someone then confirm for me that this needs to be connected to the RF pin of mr transceiever module and nothing else? I can't see where I could ground it? Thanks for any suggestions.

A whip simply connects to the output of the transmitter (and the input of the receiver of course). A whip should be mounted on a groundplane, the ground connection of the transceiver connects to that. If building it in a metal box, the metal box becomes the groundplane and the whip connects through an insulated hole to the transceiver. A whip is essentially a dipole, the other half is the reflection in the groundplane.

Presumably this unit is licence free?, if so there are strict limitations on the aerial system allowed - these are clearly given in the datasheets, so you should check on there.

BTW, for my experiments with RF modules, I simply soldered a piece of thick copper wire (2.5mm twin and earth ground wire) of the correct length to a vero pin next to the module, and obviously wired to the aerial pin. Although a groundplane is advisable (and greatly increases range), it's not essential.

 

[Mark Lazarides]

Thanks Nigel, much appreciated.

The range of the transciever units I'm using (which are at the europen free freq. 433.92Mhz) is too high and investigating attenuation techniques was next on my research list, so i'll experiment with the ground plane!

I was also considering using a variable pot in series with the antenna to achieve this? This idea was based on the maximum power principal, and not on anything I've read, so do you thik it is "sea-worthy"?

 

[Nigel Goodwin]

I was also considering using a variable pot in series with the antenna to achieve this? This idea was based on the maximum power principal, and not on anything I've read, so do you thik it is "sea-worthy"?

Why do you need less range?, it's fairly short anyway.

Adding a pot in series with the aerial doesn't sound a very good idea - the easiest thing to do is not use an aerial at all on the receiver, and see what range you get then. If it's then too short you could use a receive aerial with an attenuator - a simple pot isn't going to work too well at 433MHz.