Video from Monday 11th May's GNU Radio for Amateur Radio Astronomy meeting is now available online

[andrew....@googlemail.com]

 

Available on link below:

 

https://britastro.org/section_information_/radio-astronomy-section-overview/gnu-radio

 

Andy

_._,_._,_

 

[Stephen Arbogast]

About  this  gnu  radio  meet..     a  rational  re-sampler  block does  not  change the  frequency  it  allows  one  to resample  the  source  data stream by   a ratio  ....

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AI Overview

The Rational Resampler in GNU Radio is a DSP block used to change a signal’s sample rate by a precise fractional (rational) factor of

, where

is the interpolation factor and

is the decimation factor. 

It performs two primary operations in a single block:

• Interpolation (
  ): Increases the sample rate by inserting
  zeros between every sample.
• Decimation (
  ): Decreases the sample rate by keeping only every
  -th sample. 

Because inserting zeros creates unwanted spectral images, and decimating without filtering causes aliasing, the block uses a custom low-pass anti-aliasing/anti-imaging Finite Impulse Response (FIR) filter. 

Key Parameters

• Interpolation (
  ): The factor by which the input rate is multiplied (upsampling).
• Decimation (
  ): The factor by which the output rate is divided (downsampling).
• Taps: The coefficients for the internal low-pass filter. If left blank, GNU Radio automatically calculates taps based on the cutoff frequency.
• Fractional BW: Defines the fractional bandwidth of the prototype filter (usually left at the default of
  ). 

Common Use Cases

• Audio and Signal Processing: Converting a standard audio rate (e.g.,
  ) to another rate (e.g.,
  ).
• Software Defined Radio (SDR): Converting the raw sample rate of an SDR (like an RTL-SDR running at
  ) to a standard rate required by a downstream demodulator (e.g.,
  ). 

Pro-Tip for GNU Radio Flowgraphs

Keep your

and

values as small as possible and relatively prime (e.g., use

and

instead of

and

). Large values increase the size of the filter calculation and require more CPU and memory. 

• Rational Resampler - GNU Radio Wiki

  Jul 9, 2024 — Fractional bandwidth in (0, 0.5), measured at final freq (use 0.4) (float). In GNU Radio 3.8, the default value is 0, which should...

  GNU Radio Wiki
• Sample Rate Tutorial - GNU Radio Wiki

  Apr 4, 2024 — The output of the Quadrature Demod block has a sample rate of 960; the desired sample rate is 500. The Rational Resampler interpol...

  GNU Radio Wiki
• Rational Resampler Base - GNU Radio Wiki

  Jan 2, 2026 — Rational Resampler Base. From GNU Radio. Make a rational resampling FIR filter. If the input signal is at rate fs, then the output...

  GNU Radio Wiki

AI can make mistakes, so double-check responses

[Andrew Thornett]

Thanks for the correction.

Andy

Sent from Outlook for Android

---

From: 'Stephen Arbogast' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Sent: Saturday, May 16, 2026 5:11:13 AM
To: Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Subject: [SARA] Re: Video from Monday 11th May's GNU Radio for Amateur Radio Astronomy meeting is now available online

 

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