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@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@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@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
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@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of life speed
Sent: Tuesday, March 09, 2010 12:22 PM
To: time-nuts@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@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@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@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
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
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 Camplists@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 swedpaulswedb@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 Camplists@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
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.