Terry,
Whether you use an EMU0202 or any of the other choice for a sound
card, the issue gets down to where the 0 is. If you don't use the 8 KHz
offset, the center of your sample and the point where you are tuned
become the same. By using the offset you move the two apart by telling
the SDR software that you are using an 8 KHz. IF. This way things get a
little cleaner on the screen. However, by doing a shift, you do lose a
feature or two of the radio.
The issue of sample rate is driven by Nyquist theory for sampling.
He said you need to sample at 2X the intended bandwidth. That means to
me BOTH the I and Q data, and some DSP designers "over sample" at 3X or
or more. However to be honest, I really haven't researched this issue of
sample rate and displayed bandwidth, yet I do use it. I have only run
across this when using SDR receiver display software, so I'm not sure
what the designers are really doing. In a past incarnation, when I was
playing with early SDR's, we never went below 2X and for some dynamic
range issues we went to 4X.
The issue about using 48 KHz. is based solely on the fact that the
radio itself does not have a flat response beyond about 48 KHz. I think
there is a reference to that in the manual. And, I believe they say you
can go to 96 KHZ, but it won't be flat. This is a separate problem/issue
not associated with sampling theory.
You are quite correct. What rate you can or should sample at is
dependent on the card you go with. I went the '0202 because it was
cheaper than some of the others at the time and yet had good specs. But,
I suspect that opening this discussion up to sound card choices would be
like a discussion on what is the best antenna.:-)
73,
Barry
K3NDM
On 10/14/2013 5:39 PM, WB4JFI wrote:
Barry:
I don't have the EMU0202, so I can't say about the 8kHz shift. I do not need
to add the 8kHz shift on any of my SDR operations, however.
Regarding the sample rate versus bandwidth, when using 48ks/s, you are actually
getting TWO samples at that rate, one of I and one of Q. They each count, so
you can end up with a total of 48kHz bandwidth being displayed (plus and minus
24kHz from center frequency). That is, if you have both I and Q working
properly. That's how you get 48kHz displayed with a 48ks/s sample rate.
From what I recall (I'm out of town right now), the KX3 I/Q bandwidth is not
much more than 48k or so anyway, so sampling at 96k or higher probably won't
buy you much. But you certainly could try it. Remember that not only do you
have to deal with the KX3 I/Q output bandwidth, but some sound cards roll off
much beyond 48kHz, even if they sample at 96k or 192k. YMMV
73, Terry, WB4JFI
Sent from tfox iPad
On Oct 12, 2013, at 9:32 PM, k3...@comcast.net wrote:
Tom,
I, too, am running the EMU0202. first thing you need to do is shft the receiver
8KHz. That makes the appearance a bit better. I also notice extraneous garbage
on the display. It doesn't seem to interfere with the overall operation, so I
live with it.
Let me suggest that you not exceed 96 KHz sample bandwidth and then use the
zoom feature to look at less than the sample rate. I haven't thought it
through, but I was taught that you need to sample 2X the bandwidth. How we are
able to use a bandwidth equal to the sample rate is something I really need to
think about. But, I suspect that is contributing to some of the garbage on the
screen. And, Elecraft suggests that you should stay at 48 KHz due to internal
flatness of the radio's response, anyway.
73,
Barry
K3NDM
----- Original Message -----
From: "Tom" <tom...@videotron.ca>
To: "Barry LaZar" <k3...@comcast.net>, elecraft@mailman.qth.net
Sent: Saturday, October 12, 2013 7:27:48 PM
Subject: Re: [Elecraft] SDR software for KX3?
Hi
Well I just bought a new outboard sound card and removed all previous cards.
I'm now running an emu2020 and I can adjust the levels between the channels. I
can minimize the images but as soon as you move up or down a while the images
are back. I also have lots of spurious peaks making it impossible to
distinguish between cw and spurs. There is no adjustment in software for the
inputs but I can adjust the levels on the outside. The images look nowhere like
what you see on YouTube.
Getting pretty frustrated here
Tom
-------- Original message --------
From: Barry LaZar <k3...@comcast.net>
Date: 12/10/2013 17:28 (GMT-05:00)
To: elecraft@mailman.qth.net
Subject: Re: [Elecraft] SDR software for KX3?
Guys,
The one that really works well is NaP3. It was originally set up
for the K3, but the latest iteration does a great job on the KX3. I've
been running with the software for about a year or so, and I now don't
know how function without it.
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