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