[time-nuts] Re: Noise down-converter project

[ghf at hoffmann-hochfrequenz.de]

Am 2022-05-11 7:56, schrieb ed breya:
> The noise converter project based on the Scientific Atlanta 4647 is
> moving along nicely. Still no luck in finding any more info about this
> unit, but I did quite a bit of digging in the guts, and figured out
> enough to make progress.
> 
> The noise generator, to my surprise, is not a typical
> noise-diode-based type, but an all-amplifier deal, and apparently the
> fundamental noise source is a 75 ohm resistor in conjunction with the
> input noise of a 2N5179 amplifier front end. The first few stages are
> broadband, followed by maybe eight bandpass stages, to craft the power
> level and shape, resulting in the 50-90 MHz noise signal, which gets
> passed to the noise amplifier box.

I have once made an informal "transfer normal" between job and home.
That was just a 500?? Ohm resistor for thermal noise and two
LMH6702 amplifiers for the positions HI and LO. I used MCL PSC2-1
power dividers to add the noise to an oscillator. In my case, that
was the FEI405 once distributed here. The spurious is the FEI.

The noise source was completely flat in the bandwidth of the LMH6702s.
Beware of compression effects in the amplifier. They change noise 
statistics.

regards,
Gerhard DK4XP
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