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

[glen english LIST]

Really interesting discussion.

The reasion for my 98.304 meg synthesiser reference, it allows me to run 
the phase det at 98 megs principally to improve 5kHz-100kHz region. PLL 
BW ~ 90kHz. VCO with ADF4356Â  running at x64 (6 gigs) (393 MHz output) . 
It's quite good.

However ! performance limit <= 100Hz  is very much the reference.

So- would need to lock that 98 meg 3OT crystal so something like a 6.144 
. Wonder how effective an harmonic  injection lock here is compared to a 
PLL for the 0.1Hz to  100 Hz region. I will need to understand this 
better and do some revision and reading.....

Or start with a 6.144 or 12.88 and multiply up to 98 megs and use that, 
with any multiplier evils.

I note Rick when I re read the HP papers on the 10811Â  they had to start 
at -55 deg C..... funny.

(I have considered 98 >>doubler >> 196>>doubler >> 393 and no synth , 
but the synth provides me some get out of jail aliasing options) .

I have a ceramic dielectric resonator at 393 MHz synth output to kill 
off wideband > +10 MHz spurs (which are around -85dBc) . The $5 fix was 
very effective. (Er=90, about 20mm long ) .

 Â -glen

On 17/01/2023 8:24 pm, Magnus Danielson via time-nuts wrote:
> Hi Rick!
>
> On 2023-01-17 02:12, Richard Karlquist via time-nuts wrote:
>> Generally speaking, the 1/f noise at, say 10 Hz, for a crystal 
>> oscillator is determined entirely by the intrinsic noise of the 
>> crystal.  It's really hard to screw up an oscillator circuit so badly 
>> that it actually contributes anything to the oscillator 1/f noise.
>>
>> For instance, I'm sure we will all agree that the HP 10811 is a 
>> pretty decent oscillator.
>>
>> FYI, essentially the same crystal is used in the E1938A that I 
>> designed. Those two oscillators have ENTIRELY different circuits.  
>> Yet both achieve the same close in phase noise as what I measured for 
>> the intrinsic noise of the crystal. By the way, the HP 10811 uses a 
>> selected 2N5179 transistor.  But is NOT SELECTED FOR 1/f NOISE.  
>> Instead it is selected for good gain at high DC collector current, 
>> because the HP engineer who designed it had trouble with the 
>> oscillator starting up correctly, in conjunction with the ALC circuit.
>>
>> If you use the same output circuit for your oscillator as the 10811, 
>> you will also have no oscillator transistor contribution to far out 
>> phase noise. This is all very well documented if you want to read the 
>> details.
>>
>> In a previous life, I designed many many 5th overtone oscillators.  
>> Your crystal like the Croven ones I used in those days is not of the 
>> same caliber as the 10811 crystal, so therefore it is even more 
>> unlikely that the transistor you choose is going to make any 
>> difference.  I always locked my 5th OT crystals to something like a 
>> 10544 oscillator to clean them up close in using PLL synthesizers.  
>> The 10811 hadn't been invented yet.
>
> Good point raised here! The clean-up lock to solve close-in noise for 
> higher frequencies I think some may not have considered. As one has an 
> oscillator at higher frequency, the same loaded Q of the resonator 
> will mean higher cut-over corner for the noise. To keep 10 Hz or so to 
> be quiet, lock the high frequency oscillator to a lower frequency 
> oscillator with a narrower noise, using PLL. For odd frequencies 
> synthesis may be needed also. The PLL will high-pass filter the locked 
> oscillators close-in noise while lowpass the reference oscillators 
> close-in, so a nice cross-over.
>
> I think that is a much more reasonable approach than trying to cram 
> everything into one signle oscillator.
>
>> I hope this gets you back on the right track.
>
> Very good read. Thanks for sharing!
>
> Cheers,
> Magnus
>
>>
>> ---
>> Rick Karlquist
>> N6RK
>>
>> On 2023-01-16 14:26, glen english LIST via time-nuts 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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