[Elecraft] SDR software for KX3?

[Barry LaZar]

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, k3ndm at 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" <tomb18 at videotron.ca>
>> To: "Barry LaZar" <k3ndm at comcast.net>, elecraft at 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 <k3ndm at comcast.net>
>> Date: 12/10/2013 17:28 (GMT-05:00)
>> To: elecraft at 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.
>>