[time-nuts] Re: Low 1/f transistors for oscillator

[Bob Camp]

Hi

If you are inside 10 ppm, it’s a good bet that you are in a region that is still influenced by the
resonator / oscillator Q. At 98 MHz this is an offset of about 1 KHz. First thing to worry about 
is the Q of your resonator. 

Past that, transistors vary a lot. This brand vs that brand matters. VHF transistors are rarely
well characterized for audio noise. Their performance vs spec is not a great thing to use as a 
selection parameter. 

Simple answer is always going to be: try it and see. 

Probably better to look at 100Hz noise. At least there, you have pretty well defined limits as
to what’s ok, good, great, and impossible. As you go from -120 to -140 dbc/Hz, you pretty much
cover that entire range.

Bob

> On Jan 16, 2023, at 5:26 PM, glen english LIST via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Hi
> 
> I am embarking on building up a block - a common collector Butler oscillator with an overtone  crystal at 98.304 MHz
> 
> on on FR4 , I've used the Philips NPN type  BFS17.
> 
> The results <=10 Hz phase noise were quite disappointing. (-69 @ 98 MHz)
> 
> Does anyone have any good suggestions. Maybe something slower (larger) like a 2N5179 (or its SMT counterpart MMBT5179) will be better.
> 
> regards
> 
> glen
> 
> On 13/12/2022 11:14 am, Lux, Jim via time-nuts wrote:
>> On 12/12/22 2:43 PM, Alex Pumm
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