Re: need a LOONG delay line

"jasen" <jasen@xxxxxxxxxxx> wrote in message
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On 2006-08-18, colin <no.spam.for.me@xxxxxxxxxxxx> wrote:
"Frank Miles" <fpm@xxxxxxxxxxxxxxxx> wrote in message
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As I clearly stated digitising is out, digitising the signal would serve
no
purpose at all, it would basicaly be like comparing the signal to the
digitising reference frequency wich doesnt then even need to be delayed
to
do this, and its simpler to compare it with a reference frequency
directly.

so you're wanting to find a delay line with a propogation delay that's
more stable than a crystal oscilator?

I don't know if such even exist.

Well it only needs to be more stable averaged repeatedly over 10ms
intervals.
most oscillators are prone to 1/f noise wich seems to be most pronounced at
10hz
they are also suceptable to aceleration,
I am assuming delay lines dont suffer from 1/f noise like conducting
semiconductor junctions do,
although I know they do suffer from microphonics quite badly and also very
sensitive thermaly
its ok as long as it doesnt vary cyclicly at ~10hz.


maybe you just need a better clock?

I have quite good OCXOs at the moment, ive tried quite a few different types
of them.
they work fine when stationary. just tilting a few degrees is enough to
swamp the result.
atomic clocks still have an OXCO as a slave oscillator and so are only
marginally better over a 10ms interval
plus they are susceptable to magnetic fields.

a reference clock will drift a bit over a 10ms interval,
although it can be in a PLL the loop response needs to be over 10ms or else
it is just a duplicate of the original and serves no purpose.

But the objective is to get rid of the need for a reference frequency
altogether as this is a very limiting factor.

If delay lines were more stable then crystals people would use them for
frequency reference, but the only place I see that done is in analogue
musical instruments.

I think the reason they are not used is simply that crystals are so cheap
and easy and Q is so much higher.
there are delay line oscillators at high frequencies, SAW devices wich make
use of propogation delay make very low noise oscillators.

thanks

Colin =^.^=


.

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