[time-nuts] Wenzel oscillator - L1 value?

[Bob Camp]

Hi

There is no difference at all between a 32 pf series crystal and a 32 pf parallel crystal. They both resonate with a 32 pf load and operate at exactly the same frequency into that load. Your crystals will work fine with that circuit.

The big claim to fame of the circuit shown is that you can get a nice looking sine wave out of it at a pretty big peak to peak voltage.  It’s not bad for phase noise, but it’s also not the “super quiet” that you would expect if you paid kilo bucks for a Wenzel OCXO.

Bob

On Apr 24, 2014, at 4:07 PM, Philip Pemberton <lists at philpem.me.uk> wrote:

> I was under the impression it was a relatively low phase noise design...
> 
> In any case, my 10MHz crystals are parallel-resonant. Are there any
> alternative oscillator designs you'd suggest I look into?
> 
> Thanks,
> Phil.
> 
> 
> 
> On 24/04/14 02:38, Bob Camp wrote:
>> HI
>> 
>> The circuit they show is not very low phase noise, so adding stuff is not going to degrade it much. It will lower Q, but again, it’s not really Q limited over most of the range. 
>> 
>> The real issue with the circuit is that it has lousy load isolation. 
>> 
>> Bob
>> 
>> On Apr 23, 2014, at 9:06 PM, Tom Knox <actast at hotmail.com> wrote:
>> 
>>> Does adding these filter elements lower Q or affect Phase Noise?
>>> Thanks;
>>> 
>>> Thomas Knox
>>> 
>>> 
>>> 
>>>> From: lists at rtty.us
>>>> Date: Wed, 23 Apr 2014 17:47:26 -0400
>>>> To: time-nuts at febo.com
>>>> Subject: Re: [time-nuts] Wenzel oscillator - L1 value?
>>>> 
>>>> Hi
>>>> 
>>>> Roughly (very roughly) speaking, the series combination of C1, C2, C3 and L1 should equal the load capacitance of the crystal. If there is a varicap, it’s likely in series as well. If the crystal is cut for series, then L1 resonates with the caps in series. 
>>>> 
>>>> You can put it on a Spice program and get more accurate results. 
>>>> 
>>>> Bob
>>>> 
>>>> On Apr 23, 2014, at 10:23 AM, lists at philpem.me.uk wrote:
>>>> 
>>>>> Hi,
>>>>> I'm currently playing around with crystal oscillators (specifically a homebrew OCXO) and came across the Wenzel low-distortion crystal oscillator:
>>>>> http://www.wenzel.com/pdffiles1/pdfs/xtalosc.pdf
>>>>> 
>>>>> This uses an inductor (L1) to trim the crystal frequency, with the note that a varactor/varicap could be added to allow the frequency to be trimmed electronically.
>>>>> 
>>>>> Has anyone built one of these oscillators?
>>>>> 
>>>>> How would you pick a value for L1? I've been reading up on other crystal oscillator types (Colpitts, Clapp,...) and have yet to find anything which uses this style of frequency trimming.
>>>>> 
>>>>> Where would I add the varactor if I wanted to add EFC? Across C3?
>>>>> 
>>>>> Thanks.
>>>>> -- 
>>>>> Phil.
>>>>> philpem at philpem.me.uk
>>>>> http://www.philpem.me.uk/
>>>>> _______________________________________________
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>>>> 
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> 
> 
> -- 
> Phil.
> lists at philpem.me.uk
> http://www.philpem.me.uk/
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