Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Easy RF question

Status
Not open for further replies.

Eclipsed

New Member
I need two-way communication in a project I'm working on.I always use Linx RF modules for my RF needs.I pay around $6 for a transmitter, and around $10 for the reciever, transceivers run me about $45.My question is, can I reliably run a 1 TX and 1 RX on each end(at slightly different frequencies) instead of using a transceiver?

These are what I use-
**broken link removed**
 
i heard you can use the same frequency for the transmitter and receiver at the same end using the same oscillator. Connect it to a multiplexer of some sort and then to an antenna. The multiplexer will choose between sending and receiving.

But then i was just researching on these things for my first ever RF project. So better wait for some electronics god in this forum to reply.
 
You'd have to understand how the receivers behave in the presence of the transmitters. Even though they are on slightly different frequencies the relatively strong signal might interfere. You might experience this when you drive by a very strong FM or AM transmitter in your car while listening to the radio.

I suppose there are ways to evaluate it but just trying it might work take less time. Separate the frequencies to the extent that you can - use separate antennas and keep them as far apart as possible.

FYI - they do go so far as to put transmitters and receivers on the same antenna with very little separation in frequency. This requires additional equipment - duplexer is the word used to describe one method. A notch filter on the receive to add a little more selectivity on the front end might help.
 
The answer is yes/no/it depends!

If you want simultaneous two way communications between the ends of your link using similar frequencies for tx and rx, the answer is no. The transmitter in close proximity to the receiver will overload and de-sensitise the receiver. It is possible to add filtering to the antenna circuits to overcome this problem but the closer the tx and rx frequencies, the more difficult it is to build a filter of suitable performance.

However, if you use two widely separated frequencies which are not harmonically related, there is a very good chance it will work. Use separate antennae for tx and rx and separate them as much as you can.

Looking at the Linx website, they do frequencies arround 433Mhz and 300 (ish, cant remember exactly), if you try these, one end tx at 433Mhz the other end at 300Mhz, there is a very good chance tha this will work.

Best to check with the radio regulating authorities (FCC in the USA) to ensure that the chosen frequencies are acceptable in your country. Linx themselves may well be able to advise.

JimB
 
Thanks for the answers.I have come up with a way to keep the RX off when TXing and the TX off when RXing, which leads me to question #2, in this case can I use the same antenna for both? I should also state range in not an issue here, I've gotten 300 feet out of these modules in the past, and on this app I need a max of 20 feet.
 
OK, if you want a half duplex system that is much easier than a full duplex system.
Switching the antenna between the tx and the rx is common practice. It is (was) usually done with a relay, but generally is now done with PIN diodes, especially in low power applications such as yours.

Try Googling "Antenna Switching PIN diodes".

Here is one which I found:

www.microsemi.com/microcurrents/win98_pg5-6.pdf

JimB
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top