[time-nuts] Spectrum Analyzer Suggestions

[Magnus Danielson]

Hi Chris,

On 07/14/2013 05:50 PM, Chris Albertson wrote:
> If you are after the cheapest and smallest spectrum analyzer possible look
> for a TV tuning USB dongle.  Some of these tune over the range of 64-1700
> MHz  There is software to do FFT and plot spectrums  You can set started
> plotting in the UHF range for $20.
>
> It is a bit do it yourself in that you likely need a selection of
> attenuators and and so on because the dongle expects the signal level of a
> cable TV or TV antenna and the bandwidth is not DC to GHz.  But the cost is
> right.
>
> Here are some screen shots
> http://blog.opensecurityresearch.com/2012/06/getting-started-with-gnu-radio-and-rtl.html

Been toying around with one too.

A few notes:

1) Some tuners have a "gap" in the L-band.

2) Frequency tracing to the 28,8 MHz crystal, uncompensated. Hacking up 
a lock to a 10 MHz would improve things.

3) The RTL sampler provides you with just above 2 MS/s datastream as a 
stable rate, which limits the bandwidth in a single sweep. I have yet 
not seen a spectrum analyzer app that combines sweeps. In general I 
havve not seen a "Spectrum Analyzer" style GUI for RTLs.

4) Make sure to enable the RTL in an offset LO and not in zero LO mode, 
due to 1/f noise. Modern code supports it, but you need to enable it.

5) I have modifies mine to provide +5 V DC on the antenna, as it will 
allow for a LNA at the antenna.

Cheers,
Magnus