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 <[email protected]> wrote:
On Tue, Feb 5, 2019, 8:00 AM Bob kb8tq <[email protected] 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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