[time-nuts] OT: xtal osc PN

Bob Camp lists at rtty.us
Sun Sep 19 17:16:06 UTC 2010


Hi

The key point being that a fixed oscillator will have *much* better close in phase noise than your typical synthesized radio.

Bob


On Sep 19, 2010, at 12:41 PM, francesco messineo wrote:

> Hi Bob,
> 
> sine oscillators like the AXLE184 series (which is one of my candidate
> solutions so far) has around -110 dBc/Hz at 100 Hz offset and -160 dBc/Hz
> at 100 KHz.
> In the application I'm talking about, the use of 500 - 250 Hz crystal
> filters at the IF is normal practice.
> 
> Best regards
> Frank
> 
> On 9/19/10, Bob Camp <lists at rtty.us> wrote:
>> Hi
>> 
>> If it's a "reasonably priced" synthesized radio, -90 is probably better than
>> anything you will find on VHF  at 100 Hz offset. A lot of stuff out there is
>> closer to -60 than it is to -100. 100 Hz doesn't mess up the adjacent
>> channel rejection, so they don't worry a lot about it.
>> 
>> Bob
>> 
>> 
>> On Sep 19, 2010, at 12:04 PM, francesco messineo wrote:
>> 
>>> On 9/19/10, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
>>>> Frank,
>>>> 
>>>> On 09/19/2010 09:35 AM, francesco messineo wrote:
>>>>> Hi
>>>>> 
>>>>> On 9/19/10, Bob Camp<lists at rtty.us>  wrote:
>>>>>> Hi
>>>>>> 
>>>>>> Is -195 dbc/Hz floor good enough or is it overkill?
>>>>> 
>>>>> I'd say this is obviously overkill, -160 dBc/Hz could be a good
>>>>> compromise.
>>>>> 
>>>>>> 
>>>>>> Is -155 dbc/Hz at 100 Hz offset a requirement or is -40 dbc ok?
>>>>> 
>>>>> -40 dBc/Hz at 100 Hz is about useless, -150 dBc/Hz at 100 Hz is again
>>>>> a good compromise, the lower (practically) the better.
>>>> 
>>>> Do you *really* need -150 dBc/Hz? That is a hard requirement!
>>>> 
>>>>> It's hard to explain why to ones not familiar with weak signal
>>>>> operation between broadcasting signals, but really the noise floor
>>>>> raise a lot when you have some 5 or 6 broadcasts signals in 500 KHz of
>>>>> band (all with power levels of at least 10 dB more than the levels
>>>>> used in amateur radio, often +20 dB more)
>>>> 
>>>> I would need some more fundamental understanding of the system and needs
>>>> to be able to understand how you come up with the above noise level at
>>>> 100 Hz.
>>> 
>>> as I said, if it's not possible or not practical, of course I'll take
>>> what I can get. The receiver will be limited by its phase noise and
>>> not for example by its IMD3.
>>> I think already -110 dBc/Hz at 100 Hz is better than any LO in
>>> commercial receivers (for ham radio at least).
>>> 
>>> Best regards
>>> Frank
>>> 
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>> 
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