Basestation amplifier - but actually building one

[Da_Stier]

Hi all,

since most topics in the RF section are about tearing base station amplifiers apart, I thought it might be interesting to do it the other way around and actually build one.
I decided to build a E-GSM Frontend about a year ago. Since then I collected a lot of parts and ideas.

Since Germany also has a Corona lockdown at the moment, I finally finished the build.

Maybe a little background on why I would build a GSM Frontend.
I am really interested in cellular communication and own several GSM Testsets, where most of them simulate the basestation, however one can actually simulate the end device.
This means, that I can safely run a GSM network, using the osmocom stack and a SDR transceiver without breaking any regulation or even sending anything, since everything is cable bound.

There is a block diagram of what I built:



I used a lot of recycled material for the build.
The case comes from a broken Ethernet switch, the fans are also from some broken network equipment and a lot of components are recycled.
Even the cables for wiring everything up are reused from an ATX power supply.
This is what I came up with:













The external power supply, I currently use is a modified HP server supply, giving me 12V at up to 60A.



The internal power supply is custom made for the unit.
It accepts anywhere between 9 to 24V DC on the input. It has a reverse polarity protection and error LED for that.
It generates 27V, 12V and 5V for the internal components.
Unter full load, the unit draws 15A at 12V.



The bargraph in the front shows the current current draw.
Each LED represents 1A. If more than 10A are drawn, it stays on 10A.
If the current draw is right between two steps, both LEDs are lit up.



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The TX amplifier can output up to 30W.
The RX LNA is usable down to -120dBm of input power.

I hope this "reverse teardown" is of interest for some of you.