Transceiver RX/TX on the same pin with external LNA and PA?

Hi,

I am trying to make a RF transceiver with an external LNA and PA while sharing the same antenna. This transceiver module has one RF input/output and the software registers switch the pin function between receiving and transmitting. So my questions are:
- I was wondering if my approach of separating the LNA and the PA, as shown in the basic schematic, is correct?
- Switch 2 has to handle about 1W and such switches are expensive (no samples) - is there an inexpensive solution or an alternative design?

Since my theoretical knowledge in the RF domain is quite limited, I am mostly using already available modules and components by applying the recommended designs in the datasheets so I would appreciate any help and advise offered.


**broken link removed**

you do not say what frequency this kit is going to work at. The "blow through" of the switches is obviously paramount. Often a big bias is applied to the PA to cut of the device to stop it generating noise, which via the blow through can reduce the performance of the LNA.
Frank

you do not say what frequency this kit is going to work at.

Click to expand...

The band is 433 MHz where the modulation is FSK.

Often a big bias is applied to the PA to cut of the device to stop it generating noise

Click to expand...

In my case the data from a sensor will be transmitted once in a minute and the rest of the time the device will be waiting for instructions. Therefore while not transmitting the PA will be switched off.

Over here in Europe, the legal limit for ISM SRD devices on 433MHZ is 10 mW ERP, regardless of duty cycle.

For a switch concept for higher power, have a look at the amateur radio designs ("pin diode switch") for 70cm band (432MHz).

Over here in Europe, the legal limit for ISM SRD devices on 433MHZ is 10 mW ERP, regardless of duty cycle.

Click to expand...

The device I am making is not going to pass any certification nor has a commercial purpose. Besides I am going to use it far from any civilization so this is not going to be an issue

trastikata said:

The device I am making is not going to pass any certification nor has a commercial purpose.

Click to expand...

That makes no difference - it is strictly illegal to operate such a device, and you can get in real trouble. The frequency range is used by different services/operators, and with 1W power the range is large.

That makes no difference - it is strictly illegal to operate such a device, and you can get in real trouble. The frequency range is used by different services/operators, and with 1W power the range is large.

Click to expand...

Please let's stick to the technical part and not go in discussion about the legal issues. I am not in Europe and where and how I will be using the devise is my responsibility.