[Linrad] Re: Using Linrad and SDR-IQ for AM Radio

[Leif Asbrink <sm5bsz.com; leif@xxxxxxxxxxxxxxxx>]

Hi Eastzone,

> Maybe it is a question that not closely related to Linrad.
Yes, surely it is:-)

> I want to use SDR-IQ to listen to local AM Radio stations, since SDR-
> IQ's highest capturing BW is 40MHz and not suitable for FM stations.
It could be possible to use it for FM with a suitable converter.
I actually do not know whether the FM detector in its current
state would be any good. There will be a wideband FM mode
some day....

> I've made a GND line to the outer surface of SDR-IQ's coaxial jack,
> and inserted a 3-m long line into the center of that jack.
> 
> Next, I launch Linrad and go into AM mode. I switch the SDR-IQ's
> central frequency to the frequency of local station. No matter how I
> adjust the filter, only noises (like sounds of wind) come out of my
> loudspeakers, although I do see some meaningful patterns on the
> waterfall.
> 
> Here are some snapshots
> 
> http://farm4.static.flickr.com/3116/3240318798_b2a0074911_o.jpg
> http://farm4.static.flickr.com/3089/3240318780_445276e521_o.jpg
> 
> Do I need any special configuration on Linrad? I just used the default
> configurations of AM mode and 8kHz output sampling frequency.
To start with you need an antenna that picks up the local
radio waves rather than the interference created by your 
computer;-)

With the 3 m wire you might find that AM stations on HF
can win over the computer noise and produce some detected
AM.

Setting 8 kHz for the D/A limits the bandwidth to 4 kHz
and for a local AM station I would expect you would like
to have more bandwidth than that.

In case you have good Internet it might be a good idea to
download This file 
http://sm5bsz.com/linuxdsp/usage/kari/530-930khz.wav  
and read about it here:
http://www.sm5bsz.com/linuxdsp/usage/kari/kari.htm

In that file you can listen to plenty of local and lot 
so local AM stations and try out what the different
parameters of Linrad do to the detected AM output.

With a reasonable antenna you should se the typical symmetric
waterfall diagrams of AM stations (see e.g. kari.htm)
Then I hope you will find out what to do with Linrad
reasonably fast. Please give me feedback on anything
that you find hard to understand and that I might change
to make it easier for others.

73

Leif / SM5BSZ


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