[time-nuts] OT: xtal osc PN

francesco messineo francesco.messineo at gmail.com
Sun Sep 19 18:19:42 UTC 2010


On 9/19/10, jimlux <jimlux at earthlink.net> wrote:
> francesco messineo wrote:
>
>>>> 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).
>>
>
> But why at 100 Hz offset.  Are you looking for weak signals 100 Hz away
> from the strong interferer? (and are worried about reciprocal mixing
> from the LO)  That would imply that the interferer has equally good
> phase noise, and that's not particularly likely?

the first scenario. Even if the interferer has poor phase noise, why
folding back another share of interference on my side?
As for the 100 Hz offset, it's just a practical measure, if @100 Hz
things are good, @ 1KHz or more they must be even better, right?
In real life though, interferers are often much closer than 100 Hz to
the wanted signal and this often means no contact made (it happened
two times to me this year already).
On the other side of the contact however, the band was much more clean.

>
> If you want to be a good spectrum citizen and have a real clean
> transmitter...  (or you're doing some experiment where you are doing
> some sort of radio science, and need a clean, clean tx)
>

Clean TX is always good, but it really matters on other amateur radio
scenarios (like EME and Low Frequency among others), I don't mind
having clean TX as a side effect in my case.

Best regards
Frank



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