I am working on getting those questions answered from "the source".
-Tim
---
W4TME
FlexRadio Systems - Info Management Admin.
"Tune in Excitement"
On 10/29/2009 10:19 AM, John Ackermann N8UR wrote:
I've used the F5K with an external reference and can verify that it
works; you can see WWV's carrier jump when you plug and unplug the
external reference.
However, perhaps Tim could verify something for the time-nuts amongst
us: is the clock for the ADC locked to the same reference as the DDSs,
or is it free running?
If a free-running crystal feeds the ADC/DAC clocks, there is going to be
a frequency error due to that, even if an external reference is used.
It's likely to be small(1) and it will not scale with frequency(2).
(And just to answer a question that's likely to be asked, the crystal in
the PC does *not* contribute any error since the PC isn't doing any
analog processing.)
John
(1) Assuming the ADC/DAC are configured like a typical sound card, the
clock crystal is running at something between 10 and 30 MHz, and is
effectively divided down to the sample rate by the ADC/DAC chips. That
division both reduces frequency offset and drift, and improves phase
noise. The couple of Delta 44 cards I"ve looked at had a clocking error
of less than 1 Hertz, and were quite stable when the computer they were
housed in was at a stable operating temperature.
(2) Since the ADC/DAC are at baseband, the clock doesn't go through any
multiplication related to the operating frequency. Any offset is a
simple additive error that applies equally at all RF frequencies.
----
Mark Whatley wrote:
I was going to ask a question here today and was surprised to find
that it
was answered (I think) before I asked it! You guys are good!
I was going to ask if I connect my Z3801's 10 MHz output to my F5K
will the
Flex inherit the same accuracy as the standard?
I think the Stu might have answered that in his post but thought I
would ask
anyway. Seems like I have seen other radios that allow external
references
but they also have some oscillator along the way that is not locked to
the
reference - like a BFO oscillator - which spoils the overall accuracy.
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