[time-nuts] Auto-fail-over switch

[John Ackermann N8UR]

There is a plug-in circuit built for the HPSDR radios that detects 
presence of an external 10 MHz and when it's present shuts off power to 
the onboard oscillator.  It would probably be easy to adapt to other 
environments.  It's at http://www.k9ivb.net/Hermes/index.htm

John
----

On 2/5/19 2:09 PM, Bob kb8tq wrote:
> Hi
> 
> 
>> On Feb 5, 2019, at 11:59 AM, Mark Goldberg <marklgoldberg at gmail.com> wrote:
>>
>> On Tue, Feb 5, 2019, 8:00 AM Bob kb8tq <kb8tq at n1k.org wrote:
>>
>>> Regardless of how you do it, isolation is an issue. Having a 10 MHz
>>> standard line with a very
>>> close in spur is not a real good thing. It can mess up a lot of stuff and
>>> it passes through the
>>> cleanup loops in most gear. Is 120 db far enough down? I’ve certainly seen
>>> problems from
>>> stuff at that level at a small offset …. Simply having a switch with this
>>> or that db isolation is
>>> just a starting point. Grounding and shielding are very much on the “to
>>> do” list as well.
>>>
>>
>> I was going to mention that. I modified my Perseus SDR to use an external
>> oscillator and just removing some SMT resistors to disconnect the original
>> oscillator output was insufficient. Still coupled in a spur from the
>> original oscillator and bad close in phase noise. I had to disable the
>> original oscillator by removing power. I didn't spend the time to try to do
>> that automatically. Maintaining phase continuity in the changeover would
>> also be hard.
>>
>> Do you have any examples of something small that does this well?
> 
> Nothing that I have seen on the surplus market. Some of the things companies I’ve worked for over the
> years did a pretty good job ( at least to the specs the customer requested …).
> 
> Bob
> 
>>
>> Regards,
>>
>> Mark
>>
>>
>>>
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> 
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