Great. Thank you for the reply. Good tip about the logic Vcc.
73, Lukasz I 8
On Fri, 11 Apr 2025, 17:35 Steve Thompson via Amps, <amps@contesting.com>
wrote:
> It's almost certainly 24/28V for the main power to the driver and
> output. I used to work for a company which supplied transistors for
> other Ericsson base station equipment and everything was 28V (same with
> Nokia NMT450 gear).
>
> To check what the 'logic Vcc' supply input should be, leave power to the
> driver/output disconnected and use a bench supply to gradually increase
> the voltage while monitoring the bias voltage going to the input tabs of
> the driver and output stages. At some point the voltages should
> stabilise which will be the 'logic Vcc' that you need - probably around
> either 12V or 24V.
>
> Steve G8GSQ
>
> On 11/04/2025 08:27, Lukasz wrote:
> > 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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