[time-nuts] HP 105B Modification

Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon Dec 7 20:06:35 UTC 2009


Ed Palmer wrote:
> I have a late-model 105B Oscillator that's equipped with a 10811-60109 
> oscillator.  It seems a shame to have that nice 10 MHz source without 
> having access to it.  I was thinking of adding a buffer amp and 
> bringing out the 10 MHz signal.  It shouldn't be too hard, but before 
> I reinvent the wheel, has anyone done this and do you have any 
> suggestions or advice?
>
> Thanks,
> Ed
>
Ed

Amplifiers like those shown:
http://www.ko4bb.com/~bruce/OCXOBufferAmplifiers.html 
<http://www.ko4bb.com/%7Ebruce/OCXOBufferAmplifiers.html>

work well.
The gain is determined by the transformer turns ratio and the emitter 
series resistor value is chosen to set the output impedance to 50 ohms.
RF amplifier transistors other than the 2N3904 can be used, my 
breadboard version uses an 2N5943.
Reverse isolation is about 40dB at 10MHz. If you need more isolation 
just cascade 2 or 3 such amplifiers.
However some attentiaon to the supply decoupling is required to ensure 
that coupling via the supply doesn't degrade the reverse isolation.
In your case a nominal gain of 3dB or so should suffice.
If you need it +27dBm output is possible with an appropriate RF transistor.

Bruce





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