# DC-block block

**URL:** <https://www.ruby-forum.com/t/dc-block-block/234672>\
**Category:** GNU Radio\
**Created:** [March 20, 2015, 2:47pm UTC](https://www.ruby-forum.com/t/dc-block-block/234672 "2015-03-20T14:47:58Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [March 20, 2015, 2:47pm UTC](https://www.ruby-forum.com/t/dc-block-block/234672/1 "2015-03-20T14:47:58Z")

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I’m wanting to use the DC-block block, and I have questions about its  
use.

My scenario is to use it as a cheap high-pass, with a corner frequency  
of a few milli-hertz, with samples arriving at 50Hz.

It’s not clear how the “length” parameter relates to the desired corner  
frequency and sample rate.

Another approach I was considering was to use a long-time-constant  
single-pole IIR, and subtract the output of that from the unmolested  
sample stream.

This is for a correlation interferometer, where we want to eliminate  
stability issues caused by low-level interference from satellite signals  
that basically show up as slowly-varying DC, at a frequency that’s about  
1/10th the fringe frequency.

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**Author:** ![Marcus\_DSLeech](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/74df32/32.png) [@Marcus\_DSLeech](https://www.ruby-forum.com/u/Marcus_DSLeech)\
**Post date:** [March 20, 2015, 3:32pm UTC](https://www.ruby-forum.com/t/dc-block-block/234672/2 "2015-03-20T15:32:09Z")

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On Fri, Mar 20, 2015 at 9:45 AM, Marcus D. Leech [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> I’m wanting to use the DC-block block, and I have questions about its use.
> 
> My scenario is to use it as a cheap high-pass, with a corner frequency of a  
> few milli-hertz, with samples arriving at 50Hz.
> 
> It’s not clear how the “length” parameter relates to the desired corner  
> frequency and sample rate.

I believe this is implemented as described as a linear phase DC  
blocker in this paper:

[http://www.digitalsignallabs.com/dcblock.pdf](http://www.digitalsignallabs.com/dcblock.pdf)

I believe the “length” parameter is the “D” parameter in the moving  
average calculations.

Hopefully this helps.

Brian

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<div class="post-metadata">

**Author:** ![Marcus\_DSLeech](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/74df32/32.png) [@Marcus\_DSLeech](https://www.ruby-forum.com/u/Marcus_DSLeech)\
**Post date:** [March 20, 2015, 3:42pm UTC](https://www.ruby-forum.com/t/dc-block-block/234672/3 "2015-03-20T15:42:50Z")

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On 03/20/2015 10:25 AM, Brian P. wrote:

> [http://www.digitalsignallabs.com/dcblock.pdf](http://www.digitalsignallabs.com/dcblock.pdf)
> 
> I believe the “length” parameter is the “D” parameter in the moving  
> average calculations.
> 
> Hopefully this helps.
> 
> Brian  
> Thanks muchly. This helps a lot.

The graph at 4(a) is quite enlightening.