Hi Magnus,
If the TAPR module you are referring to is the ICS-501 thing, that is
really not suitable for this purpose. Equally, neither are the DDS
chips. Besides never being right where you want them you have the
spurii to deal with. Way too much filtering required. These two items
aside from being surface mount have the added requirement of needing a
damn cpu to tell the DDS what to do, not too mention the additional
circuit board space.
For a fixed frequency requirement it is much easier and cheaper to do it
with a proper PLL and a good but inexpensive VCXO. Which, by the way, I
found a small stash of the VCXO's on the right frequency for $25 each
from a highly reputable US manufacturer (an over stocked run). And, TOO
BOOT, I have the layout all done in through hole intended to fit in a
$15 ABS EMI/RFI shielded box about 6.7 inches by 3.3 inches.
But, thanks for the suggestions,
Bill....WB6BNQ
Magnus Danielson wrote:
Bill,
On 12/09/2013 02:30 AM, wb6bnq wrote:
Hi Dave,
My question was more centered on determining your expectations. I ran
into an even worse condition with the cheap sound card, in my shop
computer, I used for the Frequency Monitoring Tests (FMT) ran by
Connie (K5CM). Being in a space with no temperature control at all,
the sound card had a 7.0 Hertz variation over a few minutes. Clearly,
it was a crystal going wild.
As an experiment, I decided to rip out the crystal and replace it with
the output of a HF synthesizer dialed to the proper frequency. My
synthesizer, and other LAB equipment, is locked to my house standard
which is monitored (not controlled by) with GPS.
As expected, the results were spectacular ! I ended up with a
measurement process that had a resolution of 120ns, and maybe somewhat
less. At 1000 Hertz that is an uncertainty of +/- 1.2e-10. I did not
try to account for ground loops or other anomalies; and the sound card
was some cheap $18 item with no spectacular ratings in and of itself.
I am now finishing up on a project to replace my expensive commercial
synthesizer so it can return to test equipment duty. If you are
interested in what I am doing in that regard, email me about it off list.
As for the TS-2000 radio, I have not studied it, per se. But like a
lot of these modern radios there are several possible error points
within their design that could cause offsets and drift that may affect
the outcome depending upon your application.
However, if you are using a common analog detection type radio in the
"AM" mode, then the radio does not matter to the outcome. The radio
only serves as a mixer, albeit an expensive one. For example, when
comparing an approximate 10 MHz unknown signal, the mixing action
provides four (4) more decades of resolution if the output of the mix
is 1000 Hertz. If using a modern DSP radio in the "AM" mode you may
have to account for possible slight errors in the internal codecs
(A>D/D>A).
The only two error points that matter (using "AM" in the above
example) is the local signal generator used to beat against the
unknown incoming signal and the computer's sound card stability. If
both are tied to your "House Standard," then it is totally up to the
quality of your local standard's stability and accuracy.
There are dirt cheap DDS-modules to buy from China, based on AD
DDS-chip. If you need help with the reference frequency, you might want
to use that TAPR module for clock-stepup. I don't think the TAPR module
does the frequency you want straight away.
Just to give you some ideas to follow up. It will be much cheaper and
compact than your RF-generator today, and considering you already is
listening to a stepped down signal, the purity is good enough for the
purpose.
Cheers,
Magnus
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