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 <glenl...@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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