Re: crystal oscillator question...thx

From: colin (no.spam.for.me_at_ntlworld.com)
Date: 10/27/04 

Date: Wed, 27 Oct 2004 14:42:36 GMT

"Tam/WB2TT" <t-tammaru@c0mca$t.net> wrote in message
news:Xe-dnTiYP8yjPuLcRVn-tg@comcast.com...
>
> "Gareth" <me@privacy.net> wrote in message
> news:2u7kl7F27g4k6U1@uni-berlin.de...
> > Paul Burridge wrote:
> >> On Tue, 26 Oct 2004 13:36:54 GMT, "colin"
> >> <no.spam.for.me@ntlworld.com> wrote:
> >>
> >>
> >>>"Sommes" <j@jl.com> wrote in message
> >>>news:cllevg$t29$1@news-02.connect.com.au...
> >>>
> >>>>How to adjust the oscillation frequency from the output frequency of
> >>>>1MHz
> >>>>crystal oscillator?
> >>>>Thanks
> >>>>
> >>>>
> >>>
> >>>A variable capacitor, or varicap diode in series with one of the
> >>>capacitors
> >>>wil give you upto a few 100ppm adjustment depending on crystal.
> >>>
> >>>a PLL will alow u to adjust it in discrete jumps, or u can just divide
it
> >>>by
> >>>any binary number with a pre setable counter
> >>>or multiply witha mixer/multiplier to get twice the frequency, or
filter
> >>>out
> >>>the 3,5 harmonics etc.
> >>
> >>
> >> Well if you mix it and filter, you could get *any* other frequency,
> >> not just a multiple or a discrete step!
> >
> > How can you do that (unless you have another variable oscillator to mix
it
> > with, which seems a bit pointless)?
> >
> > Gareth.
> >
> > --
> > -----------------------------------------------------------------------
> > To reply to me directly:
> >
> > Replace privacy.net with: totalise DOT co DOT uk and replace me with
> > gareth.harris
>
> This is used to get a wide range oscillator. For instance, the HP 8601
used
> something like a 300 MHz xtal osc and 300 - 400 MHz VCO to get 1 - 100 MHz
> output. Highly unstable; primary use was as a sweep generator.
>
> Tam
>
>

You can use a mixer as a multiplier is what i was sugesting. ie u feed the
same signal into both input ports and get 2x frequency out +dc.

a good way to get a wide range VCO is to use a ring of 3 amplifiers with
programable bandwidth and adjustable gain in the region of -1.5. each one
introduces 60' phase shift at its uper frequency and this cuases oscilation
due to 180' phase shift negative feedback. the bandwidth and hence
oscilation frequency is a function of bias curent and this can be varied
over a very wide range.

im trying to make one for vhf/uhf, i have a ring of 3 mosfets fed from
constant curent sources, biased to about 1.5 v vds to reduce the gain to
about 1.5. At the moment it wil oscilate wel over 100mhz and 200mhz shld be
posible and if you take the sum of al three amplifiers the distortion gives
you a 3x multiplier so should see 600mhz. trying to keep
capacitances/inductances down enough is dificult using discrete components.
the lower frequency is probably determined by how well the MOSFETS are
matched.

Colin =^.^=