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

[trastikata]

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**

 

[chuckey]

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

 

[trastikata]

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

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

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.

 

[volker@muehlhaus]

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).

 

[trastikata]

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

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

 

[volker@muehlhaus]

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

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.

 

[trastikata]

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.

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.