[time-nuts] sub harmonic VCO locking

[glenlist]

Hi Bob

Yeah.  because we essentially have a sampled system, so I expect 
multiples of the injection source.

This is a sample rate clock, and so spurs that fall at 50% of the sample 
rate are OK. spurs that fall at 25% of the sample clock will appear in 
the PB. Which really tells me I need to have the injection oscillator at 
1/2 the VCO freq .  to avoid all problems.  which means x2 x2 and 
assocated filtering before the injection. I'll go back to thinking about 
doubling/ multiplication and filtering.

Given that spurs are on known frequencys, a set of symmetrically placed  
zeros either side of the output will generate a broad bandpass in the 
middle. No need for a sharp filter at least for the 1st pair of unwanted 
products....

maybe continue with you off list

cheers



On 31/07/2020 01:32, Bob kb8tq wrote:
> Hi
>
>
>
>> On Jul 30, 2020, at 7:56 AM, glen english LIST <glenlist at cortexrf.com.au> wrote:
>>
>> Before I commit the soldering iron, can anyone share their sub-harmonic injection locking experiences ?
>>
>> I have to make 393.216 from 49.152 .
>> Yes, lots of ways.... I know.
>>
>> injection locked at 1/8 of the frequency from the decent source.
>>
>> There wont be any issue of locking to the wrong harmonic, the VCO will be on the money.I was thinking of using a dielectric loaded TEM resonator  or TEM coax line VCO .
>>
>> and why do this : ?
>> - I need all the non related spurs to be > 115dB down.
> A sub-harmonic injection locked oscillator can / does have spurs at the injection frequency and
> it’s multiples ……
>
> Bob
>
>> - a double-double-double could work, but my experience is for x2 x2 x2 I really need to filter well at each stage to avoid sum and difference products.. which might be OK for this application , especially if I filter really well after the first x2 . but avoid if I can. filters at 908 MHz need space, and shield cans where it is going.
>>
>> - and I dont know too much about phase noise and SRD or varactor multipliers. but maybe that's an option.
>>
>> - my attempts at generating low phase noise x6 with class C multipliers has been dismal.
>>
>> - onboard VCO chip/PLLs have all sorts of unrelated spurs in the output.
>>
>> - sure I can use a good PLL and a external VCO, but if my N value is fixed, and I can use injection locking, why bother with the PLL chip that is likely to introduce PD related spurs anyway.
>>
>> regards
>>
>> glen
>>
>>
>>
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