Bland-Altman Analysis of Grape 1 vs Grape 2

[Charles Skoning]

Hello all, 

I thought I would compare the data from my Grape 1 vs Grape 2 for a twenty four hour period to see how close they were to each other. I used a statistical method called Bland-Altman which is used to compare two methods of measuring the same thing, in this case, Doppler shift. Here are my observations:

For my particular station my Grape 1 has a slight bias of 0.002955 Hz relative to the Grape 2.

The margin of error between the Grapes is +/- 0.001001 Hz.

I've attached a scatter plot with 95% confidence levels displayed. 

Not sure if this is useful, but I thought I would give it a go and share my results. Both Grapes agree with each other very well in my opinion.

Kind regards, 

Chuck, KE9SA

[Jonathan]

Hi Chuck,

I suspect this is due to the error introduced by the soundcard's clock on the Grape 1 as the error is mHz. This is what would account for the difference.

Jonathan

KC3EEY 

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[Jonathan]

Hi Chuck,

I wanted to show you some plots that illustrate how a soundcard's sample rate can drift over the course of the day. There is a plot, specifically the bottom subplot, that shows the drift of sample rate throughout the day on the Audio Injector Stereo soundcard. This drift is corrected with the use of a pulse per second signal from a GPS fed into the other channel of the soundcard using vlfrx-tools software. I have proposed the use of vlfrx-tools and a GPS PPS as an alternative software for the Grape.

With temperature variations throughout the day, sample rate can drift considerably enough to cause some error.

Jonathan

On Fri, Apr 12, 2024 at 1:36 PM Charles Skoning <charles...@gmail.com> wrote:

Jonathan,

Interesting, I did not consider that.

Chuck, KE9SA