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

[Bruce Griffiths]

Yes, high frequency AC current doesn't usually result in flicker noise.

Bruce

life speed wrote:
>> 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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