Frequency scanner

[a...@eartoearoak.com]

Hi, I put together an app for scanning frequencies and plotting the result. It's stable for me so I thought I should share it.

Webpage http://eartoearoak.com/software/rtlsdr-scanner

Forum http://eartoearoak.com/forum/rtlsdr-scanner

Github https://github.com/EarToEarOak/RTLSDR-Scanner

Hope you find it useful

Al

[Paul Hyde]

Hi Al,

That looks interesting.  My interest is in radio astronomy.  A year or so ago I built a simple PIC-based controller to switch my comms receiver over 80 channels, measuring the audio power as I went.  It produced promising results, showing some of the structure of solar radio bursts which are very strong at HF/VHF.  However sending a retune instruction and then waiting for an ACK over a serial link was very slow.  I only managed about 25 channels per second.

Do you have any idea how long it takes for these devices to retune, including confirming lock?

I don't (yet) have any Python experience so I'd be very interested in hearing from anyone who fancies having a go at incorporating something like this into a solar radio spectrometer.

Paul

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To: ultra-c...@googlegroups.com
Sent: Wednesday, 16 January 2013, 23:46
Subject: [ultra-cheap-sdr] Frequency scanner

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[Tony Abbey]

Hi Paul et Al (sic)

This looks like a new era is kicking off for RA. Simon (of SDR-Radio fame) hasn't come up with anything yet for RA yet, so this might be what we need. I'll start looking at the code and see if it can be modified for use with the FCDplus as well for better sensitivity/dynamic range.

Tony

[a...@eartoearoak.com]

Hi Paul,

Interesting question, I quickly tested the code and its seems to take an E4000 about 48ms to lock and a FC0012 takes 41ms. This doesn't vary with frequency or with the initial lock, which does make me wonder how good of a lock it actually gets.

For a centre frequency 'f' the program samples two 250k wide slots, one from f-500k and the other from f+250k, it then performs a simple average when overlapping slots are sampled. What was bandwidth of your channels?

[a...@eartoearoak.com]

Hi Tony,

I used Roger's library (https://github.com/roger-/pyrtlsdr) which wraps the osmocom rtl-sdr library. For the FCD it looks like gnuradio would be the best way to access it via Python.
The only other thing you'd have to change is the BANDWIDTH and OFFSET constants in the code to use the closest thing you can find to a plateau in FCDs bandwidth.

Good luck,
Al

[Paul Hyde]

Hi Al,

I simply rectified the audio (so approx. 2 kHz bandwidth) and fed it to a simple RC filter, using an ADC channel on the PIC to measure and average 64 samplesat 50us intervals.

Not sure if the attachment will work, but it shows the results of my 'narrow' scan of 75 measurements @ 10 kHz steps compared with a spectrogram from a professional instrument.  A faster scan rate would allow a wider frequency scan range, picking up the harmonic and split-band emissions at 70/140 MHz. These are all down to high energy plasma physics and there are distinct types of bursts.

Paul