From d4457469b34e6ff5799223f8e70d4d0e3dbbcdf9 Mon Sep 17 00:00:00 2001 From: Straithe Date: Thu, 15 Jul 2021 16:02:47 -0400 Subject: [PATCH] updatepicturenames (#911) * update picture names --- ...42d326d2e706e67.png => max2837-1m75bw-at-2m.png} | Bin ...42d386d2e706e67.png => max2837-1m75bw-at-8m.png} | Bin ...361434c2e6a7067.jpeg => noisereducingcable.jpeg} | Bin ...a7067.jpeg => noisereducingcablescreenshot.jpeg} | Bin docs/source/tips_tricks.rst | 11 ++++------- 5 files changed, 4 insertions(+), 7 deletions(-) rename docs/images/{68747470733a2f2f7261772e6769746875622e636f6d2f6d6f73736d616e6e2f6861636b72662f6d61737465722f646f632f77696b692f696d616765732f6261736562616e642d66696c7465722f6d6178323833372d316d373562772d61742d326d2e706e67.png => max2837-1m75bw-at-2m.png} (100%) rename docs/images/{68747470733a2f2f7261772e6769746875622e636f6d2f6d6f73736d616e6e2f6861636b72662f6d61737465722f646f632f77696b692f696d616765732f6261736562616e642d66696c7465722f6d6178323833372d316d373562772d61742d386d2e706e67.png => max2837-1m75bw-at-8m.png} (100%) rename docs/images/{687474703a2f2f6563782e696d616765732d616d617a6f6e2e636f6d2f696d616765732f492f34314943364c543361434c2e6a7067.jpeg => noisereducingcable.jpeg} (100%) rename docs/images/{687474703a2f2f692e696d6775722e636f6d2f6536344c41534b2e6a7067.jpeg => noisereducingcablescreenshot.jpeg} (100%) diff --git a/docs/images/68747470733a2f2f7261772e6769746875622e636f6d2f6d6f73736d616e6e2f6861636b72662f6d61737465722f646f632f77696b692f696d616765732f6261736562616e642d66696c7465722f6d6178323833372d316d373562772d61742d326d2e706e67.png b/docs/images/max2837-1m75bw-at-2m.png similarity index 100% rename from docs/images/68747470733a2f2f7261772e6769746875622e636f6d2f6d6f73736d616e6e2f6861636b72662f6d61737465722f646f632f77696b692f696d616765732f6261736562616e642d66696c7465722f6d6178323833372d316d373562772d61742d326d2e706e67.png rename to docs/images/max2837-1m75bw-at-2m.png diff --git a/docs/images/68747470733a2f2f7261772e6769746875622e636f6d2f6d6f73736d616e6e2f6861636b72662f6d61737465722f646f632f77696b692f696d616765732f6261736562616e642d66696c7465722f6d6178323833372d316d373562772d61742d386d2e706e67.png b/docs/images/max2837-1m75bw-at-8m.png similarity index 100% rename from docs/images/68747470733a2f2f7261772e6769746875622e636f6d2f6d6f73736d616e6e2f6861636b72662f6d61737465722f646f632f77696b692f696d616765732f6261736562616e642d66696c7465722f6d6178323833372d316d373562772d61742d386d2e706e67.png rename to docs/images/max2837-1m75bw-at-8m.png diff --git a/docs/images/687474703a2f2f6563782e696d616765732d616d617a6f6e2e636f6d2f696d616765732f492f34314943364c543361434c2e6a7067.jpeg b/docs/images/noisereducingcable.jpeg similarity index 100% rename from docs/images/687474703a2f2f6563782e696d616765732d616d617a6f6e2e636f6d2f696d616765732f492f34314943364c543361434c2e6a7067.jpeg rename to docs/images/noisereducingcable.jpeg diff --git a/docs/images/687474703a2f2f692e696d6775722e636f6d2f6536344c41534b2e6a7067.jpeg b/docs/images/noisereducingcablescreenshot.jpeg similarity index 100% rename from docs/images/687474703a2f2f692e696d6775722e636f6d2f6536344c41534b2e6a7067.jpeg rename to docs/images/noisereducingcablescreenshot.jpeg diff --git a/docs/source/tips_tricks.rst b/docs/source/tips_tricks.rst index 4d3f2df0..ef55b473 100644 --- a/docs/source/tips_tricks.rst +++ b/docs/source/tips_tricks.rst @@ -15,13 +15,10 @@ The USB cable you choose can make a big difference in what you see when using yo Screenshot before and after changing to a noise reducing cable (`view full size image `__): -.. image:: ../images/687474703a2f2f692e696d6775722e636f6d2f6536344c41534b2e6a7067.jpeg +.. image:: ../images/noisereducingcablescreenshot.jpeg :align: center -The `cable `__ used when making the screenshot for the difference in noise is: - -.. image:: ../images/687474703a2f2f6563782e696d616765732d616d617a6f6e2e636f6d2f696d616765732f492f34314943364c543361434c2e6a7067.jpeg - :align: center +A shielded cable with ferrite core was used in the right-hand image. The before and after images were both taken with the preamp on and the LNA and VGA both set to 24db. @@ -32,12 +29,12 @@ Sampling Rate and Baseband Filters Using a sampling rate of less than 8MHz is not recommended. Partly, this is because the MAX5864 (ADC/DAC chip) isn't specified to operate at less than 8MHz, and therefore, no promises are made by Maxim about how it performs. But more importantly, the baseband filter in the MAX2837 has a minimum bandwidth of 1.75MHz. It can't provide enough filtering at 2MHz sampling rate to remove substantial signal energy in adjacent spectrum (more than +/-1MHz from the tuned frequency). The MAX2837 datasheet suggests that at +/-1MHz, the filter provides only 4dB attenuation, and at +/-2MHz (where a signal would alias right into the center of your 2MHz spectrum), it attenuates about 33dB. That's significant. Here's a picture: -.. image:: ../images/68747470733a2f2f7261772e6769746875622e636f6d2f6d6f73736d616e6e2f6861636b72662f6d61737465722f646f632f77696b692f696d616765732f6261736562616e642d66696c7465722f6d6178323833372d316d373562772d61742d326d2e706e67.png +.. image:: ../images/max2837-1m75bw-at-2m.png :align: center At 8MHz sampling rate, and using the minimum 1.75MHz bandwidth filter, this is the response: -.. image:: ../images/68747470733a2f2f7261772e6769746875622e636f6d2f6d6f73736d616e6e2f6861636b72662f6d61737465722f646f632f77696b692f696d616765732f6261736562616e642d66696c7465722f6d6178323833372d316d373562772d61742d386d2e706e67.png +.. image:: ../images/max2837-1m75bw-at-8m.png :align: center You can see that the attenuation is more than 60dB at +/-2.8MHz, which is more than sufficient to remove significant adjacent spectrum interference before the ADC digitizes the baseband. If using this configuration to get a 2MHz sampling rate, use a GNU Radio block after the 8MHz source that performs a 4:1 decimation with a decently sharp low pass filter (complex filter with a cut-off of <1MHz). \ No newline at end of file