It looks like my 346A can be used down to about 2MHz with good results. This may not be the case with all 346A noise sources though, especially if they are using different diodes for the newer noise sources.
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Over the weekend, I could try and explore below 2MHz but I feel this is fairly pointless with my 346A as the ENR drops rapidly below 2MHz. However, it may be interesting to see how far down the PSA analyser can operate when I use the Noisecom noise source.
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Both are meant to work down to 200kHz. Regardless of the result, I don't see this as a practical or reliable means to measure noise figure at such low frequencies.? I don't know if the BFR91 test amplifier can maintain a flat noise figure down below 2MHz. At some point it will start to show an increase in noise figure. I could also test a common gate JFET amplifier (with a BJT second stage) as this should hopefully show low 1/f noise and flat gain from maybe 30MHz down to very low frequencies. I just need to find it...
