[time-nuts] Any reason not to use one power amplifierand splitter for distribution amplifier?
kb8tq at n1k.org
Mon Jan 5 07:47:08 EST 2015
Ok, so what does the math look like with no injection locking:
If you have two equal tones, obviously you have a hard time figuring out which one is the correct 10 MHz. That’s not going to be the situation with a distribution amp.
If you have a threat signal that’s 60 db down from the 10 MHz “carrier” that’s a single sideband signal. Run it through a limiter and you get a phase modulated / frequency modulated signal. Frequency modulating your standard line is probably not a good idea.
How much FM do you get from a signal X db down?
1) It’s a function of how far off the signal is
2) It’s a function of the level of the signal.
3) It’s a function of the limiter
If you have an objective of 1x10^-11 at 1 second, what’s that come out to?
Phase sidebands 86 db down at 1 Hz off will put you at 9.6 ppt against your 10 ppt budget.
> On Jan 4, 2015, at 11:58 PM, Bill Hawkins <bill at iaxs.net> wrote:
> Thanks, Bruce. That does clear it up, although pulling an oscillator
> through a FET gate to a 50 ohm cable seems a stretch. If things are not
> that simple, e.g., a wiring harness to a front panel selector switch,
> then maybe. I'm assuming the source oscillator is well buffered against
> the world outside the oven can.
> I should have said 10base2, not T, meaning coaxial cable with BNC
> connectors and T connectors at the receivers, terminated at the far end.
> The allusion to audiophiles had to do with people who pay hundreds of
> dollars for a line (mains) cord that has special properties to make the
> sound from their amplifier somehow more pleasant. They do this because
> marketing told them so, ignoring what goes on in the house wiring to the
> wall outlet.
> There are people who need to handle time distribution very carefully
> (lest they get FTL neutrinos), but most of the list seems to buy their
> equipment from eBay.
> Bill Hawkins
> -----Original Message-----
> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Bruce
> Sent: Sunday, January 04, 2015 3:39 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Any reason not to use one power amplifierand
> splitter for distribution amplifier?
> Almost all frequency counters have an internal source which is a
> potential means of injection locking an external reference if the
> isolation between the internal source and the external source is
> inadequate. High impedance taps on a single terminated line ensure that
> the isolation between such internal sources and the shared line is
> limited by the isolation afforded by the internal source selection
> gating/switching of each device.adding or removing a tap invariably
> changes the phase shift between the source and each of the other
> receivers.The minimum isolation required can be estimated from the
> maximum acceptable frequency shift, the resonator Q and internal reverse
> isolation between the source output and the resonator Q.
> Frequency distribution systems like the Spectracom 8140 with wide range
> ADC tend to degrade the source phase noise significantly with respect to
> non agc distribution systems.
> On Sunday, 4 January 2015 9:41 PM, Bill Hawkins <bill at iaxs.net>
> Friends in Time,
> There's been a large amount of discussion about distribution amps on
> this list.
> People may be using them just because that's what's done. So I ask you:
> What are we trying to isolate? The destination devices do not generate
> an interfering signal, n'est ce pas?
> The receiving devices do not need to have 50 ohms input impedance if the
> source cable is properly terminated, no?
> If I use high impedance receivers tapped off a terminated line, how is
> this different from 10 base T?
> Yes, there will be cable delay between receivers, but how were you going
> to avoid that with your distribution amp?
> Put another way, why do counters like the Racal 1992 allow you to choose
> 50 ohm or high impedance at the input?
> Please, no "take it on faith" audiophile answers.
> Bill Hawkins
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