[time-nuts] homebrew 13 dBm distribution amplifier based on NIST design 5 to 100 MHz

Gerhard Hoffmann dk4xp at hoffmann-hochfrequenz.de
Mon Oct 13 22:42:54 UTC 2008

On Tue, 14 Oct 2008 08:35:55 +1300, you wrote:

>     One trick that has been used for fixed frequency isolation amplifiers
>     is to use a low Q series tuned LC circuit to short out the resistor 
>     in series with the base at the frequency of interest.

Yes, but when I burn close to 3 Watts / channel and accept two transistor chains
to make it possible to get rid of of the transformers that hurt Tom's application, 
then I won't easily accept new ferrite parts that might spoil that hard won advantage. 
And all the impedance curves for ferrite beads that I have end at 500 MHz or so
and I would need them at 2.5GHz.

>     Using a suitable ferrite bead instead of the resistor may allow a
>     lower base to ground impedance at the signal frequency whilst ensuring 
>     transistor stability.
>     Such instabilities are perhaps one reason why Spectracom and NIST use
>     much lower ft transistors in their low noise 1-20MHz distribution amplifiers.

The BFG31s have the advantage that I have a reel of them in the drawer and the alternatives 
are few. Who else but NXP has a 1W PNP SMD wideband transistor in active production?
OK. At least TO-5?
Killing ft is probably the easiest part, but precise delay comes
naturally with large bandwidth.

regards, Gerhard dk4xp

(who starts thinking about T-coils and ft-doublers :-) 
Would 1 GHz distribution really be a barrier? Probably not.
I have some experience designing 10 GBit/s fiber optic XFP modules and that
should work nicely at 5GHz. )

More information about the time-nuts mailing list