[time-nuts] 10 MHz reference switching (Clay)

[Bob Camp]

Hi

Can you simply turn off the "oscillator" part of the OCXO?

In other words, leave the oven on and kill the RF at the source.

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of life speed
Sent: Tuesday, March 09, 2010 12:22 PM
To: time-nuts at febo.com
Subject: Re: [time-nuts] 10 MHz reference switching (Clay)

> Why would flicker noise be a concern if there is no dc current flowing 
> in the switches?
> Bruce

Hi Bruce,

Does it matter if the current is DC or AC?  I expect to see +/-20 mA current
due to the signal level.

Clay


From: Bob Camp <lists at rtty.us>
Subject: Re: [time-nuts] 10 MHz reference switching

> 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

Hi Bob,

I had not considered pin diode switches.  I guess in my mind they are "RF",
and 10 MHz is not.  No reason not to think about them.  However, I think to
get any sort of useable isolation at 10 MHz series-shunt or pi configuration
is required, which will have current flowing in one of the paths at all
times.

Clay

From: paul swed <paulswedb at gmail.com>
Subject: Re: [time-nuts] 10 MHz reference switching

> rf relay would work

Hi Paul,

Sorry, no relays for a high-reliability application.  Not enough room or
current either.

Clay

From: Bob Camp <lists at rtty.us>
Subject: Re: [time-nuts] 10 MHz reference switching
> Hi
> Assuming you are switching between an external reference and the internal
OCXO:
> The "bleed through" of the OCXO is going to show up as a discrete spur
close to the external reference carrier. Unless you have a very > unusual
architecture, it will be inside the loop for everything you are doing.
Attenuating it to a "suitable" level may be quite difficult. 
> Bob

Good point.  I could power down the internal oscillator based on a detected
external reference.  Just more circuits to add . . .

Thanks to all who replied, you raised some good points.  Locking the
internal to external sounds better all the time, it's just kind of
expensive.

Clay


      

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