Aliexpress LoRa Amplifier AB-IOT-433

I've been experimenting with APRS using the T-Beam LoRa hardware, as described in Andreas Spiess HB9BLA Wireless' YouTube video here. (Andreas has two YouTube channels, both are very much worth subscribing to, here and here.)

Now the standard T-beam hardware outputs around 100mW, and I'm getting a range of around 9 miles, although one packet managed to make a 12 mile journey one morning!

Perhaps a little more output power would help.

AliExpress advertises a small RX/TX amplifier. A quick search for "Lora amplifier" pulls up a few, and I bought this one.

It arrives from the seller very promptly. 

It advertises a 2.3W output power at 5V supply, so you will need to have a suitable license to operate this. I have a ham radio license, so I'm good on 433 MHz.

I gave it a quick test on the bench, and it makes 2W happily at 5V, so a real improvement, however the second harmonic is not very well suppressed... 

We're going to need a simple filter. 

Using the tracking oscillator of my Spectrum analyser, I cut an open circuit length of coax to make a suitable stub filter, and once it's cut to the correct length, It's connected via an SMA T connector to the output. 

The output is measured again...


Much improved :) 

I've curled up the stub, which does not effect it's performance, and connected the amp up. It's probably best not to run the amplifier without an antenna or load connected. 

Lashed up in the car for testing... 

And the range now?

Almost no change! I'm not sure what I was expecting. UHF at these frequencies is very line-of-sight, and the range in this case is ultimately defined by terrain. A testament to the robustness of the LoRa protocol at just 100mW, and an interesting, but ultimately pointless experiment! 

Thanks to Jayne, M0JNE, for her help and thoughts on this project.