Display Response at the Centre Frequency.

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Display Response at the Centre Frequency.

gm3sbc
Hello All,

When I am operating  Softrock type hardware I find that there is a significant dip in the frequency response near the Zero IF position on the screen.

Is there a possibility of reducing the frequency LF cut-off value so that the dip amplitude can be reduced.

I have tried to find the area of the code where this may be defined but with no luck.

Any ideas would be appreciated.

Regards

Ed GM3SBC  
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Re: Display Response at the Centre Frequency.

ahlstromjc
Administrator
Hello Ed,

The dip at zero Hertz is caused by the sound card low frequency response. Quisk does have a filter at zero Hertz to get rid of DC, but it is very narrow.

Jim
N2ADR
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Re: Display Response at the Centre Frequency.

gm3sbc
In reply to this post by gm3sbc
Hello Jim,

Sorry for being so late in replying to your response. Pressure of work !

I find that if I use HDSDR of Flex PSDR I do not get the large dip at DC. The Dip is approximately 1 KHz wide. ie +/- 500 Hz.

Is it possible for me to remove your present DC correction. Even an indication in the code where I could possibly modify it for a test.

Regards
Ed GM3SBC
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Re: Display Response at the Centre Frequency.

ahlstromjc
Administrator
Hello Ed,

The DC removal is in each sound driver, for example, sound_alsa.c. Look for the text "// DC removal". Remove the code and recompile.

Jim
N2ADR