RF Amplifier Design Help

[sreekdr729]

Hi,

I am designing an RF amplifier for the ISM band for a specific project. The idea is range improvement. We attached a CMX90A004 evaluation board to our transceiver module and we achieved increased range. But the same system with the RF amplifier while receiving back signals is attenuating the RX signal. I have turned off the RF amplifier module by driving low to the CONTROL voltage, while in RX mode.

Q1. Is this an expected behavior or a design issue?

I am planning to use an RF SWITCH to switch between the TX path and the RX path. It may work.

Q2. Please suggest the right design approach while considering an RF amplifier for LORA system.

 

[aliarifat794]

To improve sensitivity and range you can add an LNA in the RX path.

 

[danadakk]

Is your RF switch decoupling the PA output when in Rx mode ?

If you are powering it off to rely on disconnect use your Nano VNA and
look at PA output Z to see if its a passive matching network solution,
hence powered off probably still presents 50 ohms onto antenna loading it.

 

[sreekdr729]

To improve sensitivity and range you can add an LNA in the RX path.

To clarify, both the TX and RX path are the same for my transceiver.

 

[sreekdr729]

This is the first scenario I am talking about. The RF amplifier is amplifying the TX signal properly. Since I use the same antenna for receiving the signal, although the RF amplifier is off, it is attenuating the RX signal

 

[sreekdr729]

This is the second scenario where I am planning to use an RF switch to alternate between TX and RX paths.

My query is whether the issue I am facing in the first scenario is expected or not. If the issue that I am facing for my RX signal is due to selection of component, then please suggest the correct design approach

 

[FvM]

Usual solution is having two SPDT switches, one at transceiver and one at antenna side. RX path can either go straight through both switches or use a LNA inbetween.

 

[D.A.(Tony)Stewart]

For example in Europe when using the ISM band frequencies (863 MHz - 870 MHz) users must comply to the following rules: For uplink, the maximum transmission power is limited to 25mW (14 dBm).

• For downlink (for 869.525MHz), the maximum transmission power is limited to 0.5W (27 dBm)
• There is an 0.1% and 1.0% duty cycle per day depending on the channel.
• Maximum allowed antenna gain +2.15 dBi.

What is your path loss budget? SNR, Rx threshold, IF filter response antenna gain?.

on web

https://www.mouser.ca/c/passive-components/?frequency%20range=902%20MHz%20to%20928%20MHz&product=SAW%20Filters&termination%20style=SMD%2FSMT