Pick pretty much any 2m FM receiver design you like, recalculate the front end and your mixer for 137.5 MHz and then adjust the I.F. bandwidth to 40 KHz, APT is a 2400 Hz carrier that is Amplitude Modulated on a FM Carrier at 87% modulation which makes it about 34 KHz wide, any receiver design should have AFC or some sort of frequency control to compensate for Doppler or you will need to make your I.F. filter a little wider to keep the signal in the passband.

Kevin WA6FWF

A good example is the RX2 http://www.time-step.com/rig//pdfs/rx2c%20instruction_20.pdf

On 12/5/2014 1:34 AM, Rupesh Lad wrote:

Hello all;

I am an undergraduate Engineering student and a SWL. I have tracked many Amateur satellites from COEP Ground station, VU2COE.

I want to Home brew a NOAA satellite image receiver as my academic project. I will be using WXtoImg to decode the image transmitted by NOAA satellite on APT frequency. So the task for me is to get the audio frequency output.

Literature says that NOAA satellites transmit a signal of 40 kHz bandwidth. I have also observed the spectrum on Spectrum analyzer using my antenna. Want to know whether this is only RF bandwidth? and if it is so, then what is IF bandwidth of such signals?

Can anyone help us in designing the receiver?

Hi,

I used a Funcube Dongle and gnuradio. You do need the 40 (34)kHz bw. Google for OZ9AEC, Gnuradio, NOAA.

Alex has done it in gnuradio. I have also done it in gnuradio [to be honest most of it was "borrowed" from Alex]

See http://hal.g7iii.net/POES/FlowGraphs/POES_Live_Decode_Annotated.png

If you patch in a resampler (to 11.025kHz) between the FM Demod and Audio sink blocks, you can send that to an ALSA loopback sound device, and connect wxtoimg to the other end.

See (unannotated, and with extra debug, dual output so I could compare, and other features):

http://hal.g7iii.net/POES/FlowGraphs/POES_Live_WXtoIMG.grc.png

Plenty of received pictures at http://hal.g7iii.net/POES/

Iain

On 05/12/14 22:29, jkelly wrote:

I believe the bandwidth is less - but due to doppler they spec a 40khz bandpass so the 34khz signal can slide within the 40khz receiver.

This link might be helpful:

http://en.wikipedia.org/wiki/Automatic_Picture_Transmission

Jeff K2SDR

http://wx.k2sdr.com

On 12/5/2014 4:34, Rupesh Lad wrote:

...

Hello all;

I am an undergraduate Engineering student and a SWL. I have tracked many Amateur satellites from COEP Ground station, VU2COE.

I want to Home brew a NOAA satellite image receiver as my academic project. I will be using WXtoImg to decode the image transmitted by NOAA satellite on APT frequency. So the task for me is to get the audio frequency output.

Literature says that NOAA satellites transmit a signal of 40 kHz bandwidth. I have also observed the spectrum on Spectrum analyzer using my antenna. Want to know whether this is only RF bandwidth? and if it is so, then what is IF bandwidth of such signals?

Can anyone help us in designing the receiver?

---

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