Meshtastic US-915 MHz and EU-868 MHz Bidirectional RF Amplifier AB-89 Overview by Technology Master

[@DawnPatrol-ce5rk]

Thankyou SO much for finding a way to simply explain all the meshtastic particulars that nobody else seems to address.....Greatful!

[@technologymasterkam]

You're very welcome!

[@SeptemberRain8888]

I ordered two of them and will see how they perform.

[@TEKENGLOBAL]

Please make a video showing how everything is connected using this amplifier.

[@technologymasterkam]

Just added in TODO list. Thank you for the valuable suggestion.

[@davidalbert9387]

Do you put the saw filter between the amplifier and antenna or between the radio and amplifier?

[@technologymasterkam]

It is tricky. I PUT IT BETWEEN RADIO AND AMPLIFIER. Radio is usually the main source of harmonics and amplifier has no or very little contribution to harmonics. I will put filter between ANT and amplifier if there is too much interference in the area and my priority is to increase receiver sensitivity (remember this is a bidirectional amplifier i.e amplifier for TX and LNA for RX side). There is a 3rd scenario where I cannot ignore harmonics and I need best selectivity for LNA. I would go for two filters i.e one for TX between radio and amplifier and other for RX between Ant and amplifier(LNA)

[@fotografm]

That looks very useful ! Where can I buy it ???

[@technologymasterkam]

It is available on aliexpress. Available from many vendors. www.aliexpress.com/item/1005005445930926.html Option is Color: 868M Filter 2in1 B. I have seen people complaining and saying that they threw it away. In my view there are two most common reasons for problems with RF amplifiers. 1- Unstable and starving power supply. It has to be able to provide sufficient current with stable voltage when we are transmitting. 2- Is the overdrive. We should start at a lower dbm and keep increasing while keeping an eye on its performance. I know you are a master of Meshtastic, still adding my 2 cents. :)

[@fotografm]

@@technologymasterkam thank you for the info. Will take a look !

[@paveljeludovsky]

@@technologymasterkam Have you done any tests for the overdrive? it seems that the default TX gain is 0. Have you tried to increase it? What's the default TX gain that it comes with? What was the TX gain that worked best for you? And thanks for all the informative videos you create.

[@technologymasterkam]

I have not tried overdrive as it is not recommended by Semtech and others too. I usually keep drive a bit below the upper limit given in the specs. It produces unwanted noise and signals due to unstable or over voltage. When using an amplifier, we can start with minimal drive and then increase it keeping an eye on the received signal. - I am not aware of any default value. I have seen different value from different manufacturers. Mostly it is 22dbm. If we increase this TX value in the software, actual transmission still stays at MAX e.g 22dbm. - I usually use 22dbm while using node without amplifier. In my videos I have shown what value I am using for a specific test or experiment. If I have missed it somewhere or if you have a question about a video, do ask :)

[@paveljeludovsky]

@@technologymasterkam I was asking if you've tried the different TX levels on the amplifier. From what i see, the amplifier in your video comes with a default tx gain of 0.