rx2fits code posting

[Nathan]

I posted a linux code for spectroscopy using the rx888mk2 receiver to Source Forge under the name rx2fits.  It streams spectral data with frequency from 0 to 65 MHz to FITS files. This code is for the direct-sampling input of the receiver, which transmits real samples over USB3 at up to 130 MHz sample rate.  rx2fits processes these samples to spectral intensities via a Fourier-transform poly-phase filter bank (PFB).  Sample rate, Fourier bin count, PFB frame count, integration time and receiver gain parameters can be set.  Utilities for device enumeration, firmware upload, display of FITS header, file viewing, and for measuring sample rate and sample statistics are provided.  Dropped samples at 130 MHz are negligible.  The file viewer is written in python with capability for panning and zooming, dividing out model response functions, and background subtraction.  There is an installer for dependencies.

To run at 130 MHz, the code needs a modest desktop computer.

Dynamic spectra generated by the code are posted at this link.

Nathan

[Don Latham]

best price I found $140

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From: "Nathan" <tow...@ownmail.net>
To: "sara" <sara...@googlegroups.com>
Sent: Thursday, June 6, 2024 6:35:53 PM
Subject: [SARA] rx2fits code posting

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Don Latham
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[Jan Lustrup]

Hi, Nathan,

Any way it could go higher in frequency? Like up to 90MHz? (not using an external converter).

 

Jan Lustrup LA3EQ

 

From: sara...@googlegroups.com [mailto:sara...@googlegroups.com] On Behalf Of Nathan
Sent: fredag 7. juni 2024 02:36
To: sara...@googlegroups.com
Subject: [SARA] rx2fits code posting

 

I posted a linux code for spectroscopy using the rx888mk2 receiver to Source Forge under the name rx2fits.  It streams spectral data with frequency from 0 to 65 MHz to FITS files. This code is for the direct-sampling input of the receiver, which transmits real samples over USB3 at up to 130 MHz sample rate.  rx2fits processes these samples to spectral intensities via a Fourier-transform poly-phase filter bank (PFB).  Sample rate, Fourier bin count, PFB frame count, integration time and receiver gain parameters can be set.  Utilities for device enumeration, firmware upload, display of FITS header, file viewing, and for measuring sample rate and sample statistics are provided.  Dropped samples at 130 MHz are negligible.  The file viewer is written in python with capability for panning and zooming, dividing out model response functions, and background subtraction.  There is an installer for dependencies.

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[Nathan]

Jan,

The ADC sample-rate rating of 130 MHz is the main limitation.  I ran it at 150 MHz over night without data loss and perhaps that rate can be sustained.  There is also a low-pass filter with 65 MHz corner frequency in the device, which I think can be used to 75 MHz before bypassing is necessary.  But I am using an older version of the Cypress chip code with an issue that prevents running above 150 MHz.  Getting past that for higher sample-rate testing is a problem.  There is a drop-in replacement ADC that can run at 160 MHz (perhaps higher), but installing it is the issue.

I agree covering  up to the FM band is desirable.  As well as dual-polarization.  There is a lot going on in receiver development now.

Nathan

On 6/7/24 01:13, Jan Lustrup wrote:

[Jan Lustrup]

Thanks Nathan. That explanes the issue. Jan

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[Jonathan Pettingale]

Nathan,

What antenna are you using on the rx888? Having seen your post, I went out and bought a rx888. The software works fine, you have done a great job on it!!

Jonathan Pettingale

[Nathan Towne]

Hi Jonathan,

I am happy it is working for you.  For an antenna I am currently using a LWA balun board available from Whit Reeve and a pair of drooping loops of 14 gauge wiring intending to imitate the LWA antennas.  Perhaps 4 meters span.  There is a 30 meter RG-58 cable run with pads at each end to suppress standing waves and their gain modulation.  I also put a high-pass filter consisting of a 120 pF capacitor in series with the cable center conductor at the receiver end to reduce intense interferers at lower frequencies.  Compensate the gain reduction with the hpf feature of the viewer.  I have modified the board to provide power over separate wires.

Another option is to use the full LWA antenna-stand assembly, but it is (more) pricey.

For initial testing I used a four meter simple dipole using RG-59 and the ferrite beads used in the Radio Jove antennas (no balun board).  

Nathan

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  Nathan Towne

  tow...@ownmail.net