Rick,
Depending on the "card" (it's more like USB dongle now) and their
choices of ADCs and DACs, you may or may not bypass the DC blocking caps.
I know that people playing around with laser-shows use this trick, but
it was quite some time since I look at was is available.
Would be interesting to see what is available.
If one has ADCs and DACs, when one could implement the loop in digital,
which have the additional benefit that adjusting it can be automated.
Cheers,
Magnus
On 03/24/2016 02:31 PM, Richard (Rick) Karlquist wrote:
Thanks for the explanation. I actually built
something like that 30 years ago using an LT-1028
op amp, only it used an HP3582 FFT box instead of
a sound card (which didn't exist at the time).
Does anyone have any experience with the low
frequency cutoff of sound cards? You would
think 20 Hz, but maybe they go lower?? Any
recommended sound cards (or USB things that
work like sound cards)?
Rick
On 3/24/2016 4:42 AM, Bob Camp wrote:
Hi
Pretty simple:
Double balanced mixer, RPD-1 is one option, there are others.
Fairly simple L/C lowpass between the mixer and an op-amp.
20 db positive (non-inverting) op-amp amplifier string after the mixer
Output of the string goes to the sound card. Use a good (dual / quad)
audio op amp
Quadrature amp picks off the output of the first op amp stage, switch
and resistors to set gain, pot to set op point.
====
So what you have is an old style quadrature phase noise amp and “PLL”.
More or less a very junior version
of the 3048 test box. Like any setup of this sort, you check two
similar oscillators. They run in quadrature and
you do a few “measure this with switch in position A” sort of things
to set things up each time.
Nothing exotic.
Bob
On Mar 24, 2016, at 12:25 AM, Richard (Rick) Karlquist
<[email protected]> wrote:
On 3/23/2016 3:56 PM, Bob Camp wrote:
and standard covered. If you want to do spurs, spend $40 and build a
phase
noise test set that will drive the sound card on your PC.
Lots of choices ….
Bob
Any documentation on this $40 phase noise test set?
Rick N6RK
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