I run a LynxOne sound card. It has clock in and out (75 ohms- TTL).
The clock can be 25 Khz to 27 Mhz. In its control software, it can use
a 13.5 Mhz video dot clock, a 27 Mhz video dot clock, a word clock or a
X256 word clock.
I had considered using a synthesizer to locked up the sound card to the
rubidium during the ARRL frequency test back a few years ago. I worked
out everything in advance. I had a heart attack about 2 hours before
the contest - so I never got to work the contest...
I did not buy the card for the clock capability. It was bought because
it could handle 24 bit resolution and had digital and analog ins/outs.
You can also use multiple cards and the way they slave them, is via the
clock.
Brian N4FMN
John Ackermann N8UR wrote:
Alberto di Bene wrote:
Hmmm, the sound card used is the M-Audio Delta 44, a professional sound
card, used also by musicians and composers for studio works. I don't
know the accuracy of its time base, but certainly it is quite good.
I previously did some rough accuracy tests of my Delta 44 cards and
found they were "pretty good" but I didn't record the results.
Just for the fun of it, I am now measuring one and see about a 1.5Hz
error at 25kHz -- that's 6x10e5. The setup is an HP3325A synthesizer,
locked to an Rb standard, feeding 0.5v p-p into the Delta 44 on an
Athlon 2200 running the Linux-based Baudline spectrum analyzer program.
I'm sampling at 96kHz and decimating by 4096; Baudline has a very cool
measurement function that will give the absolute frequency reading with
a resolution of better than a mHz. I'm measuring ~24998.5Hz against the
nominal 25000Hz. The Delta 44 has been running in the computer for
several weeks, so it should be thermally stable. I've attached a
screenshot of the Baudline display.
One thing I want to explore is how difficult it would be to provide an
external clock for the Delta 44. Higher-end boards in the M-Audio
series have a "wordclock" input, and I suspect that the Delta 44 PC
board may be hackable to enable that.
John
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