[time-nuts] sub harmonic VCO locking

[Bob kb8tq]

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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