I've recently got my hands on some ancient mobile phone base station
amplifiers which I've managed to retune to 435Mhz +- 5MHz but I need some
help with choosing the voltage to run them at.
Does anyone in this group have any knowledge of such old cellular hardware?
Specifically power and logic voltages used?
These amplifiers are only 50W, but they are very nice if one wants to bump
a -10dBm SDR output to usable power (got 12W from -5dBm at 12V) to use one
of the high frequency SDRs like Lime (or maybe Pluto, I use Limesdr).
The amplifiers use bipolar transistors in a 5 stage design. First 2 stages
are in a little metal can and they are two of BCP54 transistors (45V max)
with 3 unable core filter cans between them. Also same transistors are used
to switch power to other RF stages.
Then there is SGS Thomson 1310 transistor, 1391 and finally 1393. As far as
I can tell with my nanovna probing first 4 stages are very wideband (pretty
much flat between 300Mhz and 600mhz) and the filter cans are used to narrow
the input down.
The final transistor uses a tuned input but it's output again is very
wideband (3dB bandwidth is again over 300mhz). So all i had to tune were
the input cans and anf the input circuit of the final.
The thing is powered by an 11 pin plug. First two pins appear to go
directly to the final and one prior transistor power supply. Then we have
something I called "logic Vcc" it is power for a quad op amp circuit that
sets the bias, the 1391 and other transistors thar switch power on/off.
This is the voltage I'm mostly trying to find. It works from as low as 5V,
but it produces a lot more power at 12V.
Then there are tewo enable pins that have to be over 3V for bias and power
to be supplied.
I haven't discovered the purpose of other pins, but I suspect they might be
status outputs.
I know all transistors can survive 40V. I believe the final may have run on
24V.
But not sure about that logic supply that also powers 1310 transistor and
earlier stages. The opamp (3303) is fine with up to 36V (+-18V). But I have
no way of knowing how these bias circuits are set (there are smd pots).
Can anyone suggest how to find the correct value for that voltage?
73, Lukasz
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