[time-nuts] 10 MHz reference switching

[paul swed]

rf relay would work

On Mon, Mar 8, 2010 at 6:51 PM, Bob Camp <lists at rtty.us> wrote:

> Hi
>
> Or put another way:
>
> If you have a structure that uses series resistors and shunt diodes:
>
> The diodes are reverse biased when the switch is "on".
>
> The diodes are forward biassed when the switch is "off".
>
> No current when on = no noise.
>
> Bob
>
>
> On Mar 8, 2010, at 6:43 PM, Bruce Griffiths wrote:
>
> > life speed wrote:
> >> Hello Time Nuts,
> >>
> >> I'm back again.  I designed bandwidth-limited (30 MHz) ADA4899-1 opamp
> circuits to buffer the 10 MHz reference, with theoretical noise of less than
> 3 nV/rtHz.  Oscillator noise is about -155 dBc/rtHz from 1 KHz to 10 KHz,
> and -160 dBc/rtHz from 10 KHz to 100 KHz.  Unfortunately the rest of the
> design is holding up PCB manufacture, so results on these won't be available
> for awhile.
> >>
> >> Which brings me to the other design-stopping considerations:  Is anybody
> aware of low-noise analog switches that can be used to reconfigure the 10
> MHz reference paths without significantly degrading the phase noise?  As
> always, I believe 1/F noise would be the concern.  Non-reflective is great,
> but I can accomplish that by using more switches and 50 ohm resistors if
> need be.  Isolation is a key consideration as well.  Mechanical relays are
> out of the question.
> >>
> >> An alternative to switching is phase-locking the OCXO to an external
> reference.  I have thoroughly looked into this possibility, and it is likely
> my preferred approach.  But I need to understand how the switching approach
> compares, hence my question.  I do not need help with phase-locking; this
> feature is readily available from OCXO vendors who have dedicated years of
> research to optimizing their products.
> >>
> >> Any switch experience out there?
> >>
> >>
> > Why would flicker noise be a concern if there is no dc current flowing in
> the switches?
> >
> > Bruce
> >
> >
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