Spectrogram

[VE3WDM]

Hi all,
I am going to start setting up my K2 and will be using Spectrogram for  
some of the steps. I downloaded ver 5.17 onto my laptop. Setup the  
scan input page according to N0SS website. With no input the scan  
input screen has the normal rise up to -20 then it dropes to -60.  
Where it is suppose to stay but I have some ripples up around -40. Is  
there an adjustment in the sound card I need to do? Or does one of the  
scan input values need to be changed?
Mike
VE3WDM

Sent from my iPhone
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[Don Wilhelm-4]

Mike,

Are you using the mic input or does your laptop have a line-in?  You may
be seeing the baseline noise of your soundcard input - some are noisier
than others, and if you have an open input, that may be picking up noise
- Spectrogram will display that open circuit noise pickup.  Short the
input and see if it changes.

In any case, I would not worry about it - it may just be some artifact
of the soundcard that will not be relevant to what you are trying to
accomplish.  Put some kind of input into the soundcard and adjust the
audio input level to place the display at some convenient point on the
screen.   You may have to adjust the sliders in your soundcard control
panel, and adjust the audio level you are feeding to the soundcard.  Try
it - connect a cable between the K2 headphone jack and the soundcard,
then play with it for a bit with both a single signal tuned on the K2
and with a wideband noise input to the K2 (even band noise will work).  
Once you see it, you will have a better feel for what is going on.  A
single tone signal will appear as a spike on the display at the audio
frequency indicated on the horizontal scale - and the filter passband
will be a wider "hump" on the display (at a lower amplitude than the
signal).  Adjust the levels and the slider on the right of the screen to
place the display on the screen vertically anywhere you want to see it -
then you can say that some signal is xx dB above the receiver noise
floor, or if there are two signals, you can say that they are xx dB
different from each other, or with only a wideband noise source into the
K2, you can see the relative amplitude of the passband at various audio
frequencies.

A spectral line display is always relative on the vertical scale, it
never shows any absolute value.  The information that is conveyed is
that one point is xx dB different than some other point.  That is true
with any spectrum analyzer type display.

73,
Don W3FPR

Mike wrote:

> Hi all,
> I am going to start setting up my K2 and will be using Spectrogram for  
> some of the steps. I downloaded ver 5.17 onto my laptop. Setup the  
> scan input page according to N0SS website. With no input the scan  
> input screen has the normal rise up to -20 then it dropes to -60.  
> Where it is suppose to stay but I have some ripples up around -40. Is  
> there an adjustment in the sound card I need to do? Or does one of the  
> scan input values need to be changed?
> Mike
> VE3WDM
>  
>

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[k6dgw]

Mike wrote:

> I am going to start setting up my K2 and will be using Spectrogram for
> some of the steps. I downloaded ver 5.17 onto my laptop. Setup the scan
> input page according to N0SS website. With no input the scan input
> screen has the normal rise up to -20 then it dropes to -60. Where it is
> suppose to stay but I have some ripples up around -40. Is there an
> adjustment in the sound card I need to do? Or does one of the scan input
> values need to be changed?

I first used Spectrogram on a cheap, POJ Gateway laptop I bought when I
retired and turned in the company's laptop.  I had noise in the display
sufficient to mask the audio being fed in from my K2.  I tried bonding
the K2 and laptop grounds together, grounding and ungrounding, and was
about give up when I unplugged the laptop power.  Noise totally went
away.  If you're on a laptop, it would be worth a try.

I no longer have the Gateway.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2009 Cal QSO Party  3-4 Oct 2009
- www.cqp.org
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