[time-nuts] New topics (was Re: He isa Time-Nut Troublemaker....)

Magnus Danielson magnus at rubidium.dyndns.org
Wed Dec 24 01:04:38 UTC 2008


Didier skrev:
> John,
> 
> When you add two (statistically independent) 5 MHz signals and get a 10MHz
> signal, the 10 MHz signal's *relative* noise and drift will be the average
> of the *relative* noise and drift of the two 5 MHz signals.

Not to ruin your analogy here, but what I was discussing on interlocking 
was intended as means to phase-lock the two oscillators (say 5 MHz but I 
was thinking 10 MHz) and you could then just add their sines, not mix 
them up. Thus, you do not get the sum frequency, you get the average 
frequency. Of course you could go for the frequency multiplication 
variant if you want.

> So as when you average n signals, the noise and drift are reduced by sq.rt of n, in this
> case, 1.4, or about 2dB (if I am correct), a modest improvement. 

Square root of 2 is about 1,414 or about 3,01 dB.

> Combining more than 2 signals that way (to get more than 2dB improvement)
> gets complicated in a hurry.

Actually no. Not really. You can build pairs and then interconnect them 
together the same way to form a quad, and so you go on. The neat thing 
is that the combined oscillators behave as a new oscillator. This is a 
very traditional way of combining sources to reduce noise. It is 
certainly not new.

> I guess the idea behind differential locking was to simplify the circuit so
> that a large n could be used to get meaningful improvement without too much
> additional circuitry.

Indeed.

Cheers,
Magnus



More information about the time-nuts mailing list