Re: Fw: [Discuss-gnuradio] AO-51 and GRC

[Alexandru Csete]

Hi Patrik,

Thanks again for the info. I like your home made yagi antenna for UHF.
I will try to build one in the holidays.

Implementing Doppler correction in GNU Radio receiver can be
relatively easy. I can think of three ideas with increasing complexity
and performance:

1. Make the filter in front of the FM detector wide enough to cover
the satellite downlink +/- Doppler shift. I think for voice FM it will
be okay if you are a few kHz off as long as you get the whole signal
through the filter.
2. Active Doppler correction using satellite tracking code. There is a
python library called pyephem that you can use to calculate satellite
position, range and range rate, hence Doppler shift:
http://rhodesmill.org/pyephem/
3. Track the center frequency of the carrier using the FFT spectrum.
For voice FM this is easy because of constant amplitude. Even when the
signal is fading, the peak in the frequency domain will correspond to
the center frequency as long as you have decent SNR. You can try to
visualize it using a waterfall sink.

Cheers
Alex


2009/12/8 Patrik Tast <address@hidden>:
> Hi Alex,
>
> I used a 1.2 m long X-yagi and a cheap broadband TV pre-amp
> http://www.vekoy.com/product_info.php?cPath=85_402&products_id=12828
>
> EZNEC told me I should get ~14 dB Gain with this gadget, It sure works!
> The boom is a PVC pipe and elements are 3.2 mm Al/Ag TIG welding rods, < $20
>
> An image of the antenna and txt how I made the X-Yagi is at
> http://www.poes-weather.com/~patrik/AO-51/
>
> It is tricky to follow the downlink frequency change due to doppler....
> Patrik
>
>
> ----- Original Message ----- From: "Alexandru Csete" <address@hidden>
> To: <address@hidden>
> Sent: Tuesday, December 08, 2009 12:02
> Subject: Re: Fw: [Discuss-gnuradio] AO-51 and GRC
>
>
>> Hi Patrik,
>>
>> Thanks for the info. It's quite good reception you have with the TVRX.
>> Did you use any low noise amplifier in front of the TVRX?
>>
>> Cheers
>>
>> Alex
>>
>> 2009/12/8 Patrik Tast <address@hidden>:
>>>
>>> Hi Alex & All,
>>>
>>> I use the usrp_nbfm_rcv.py in examples to listen on OSCAR.
>>> Here is a sample audio recording I made a few week ago
>>> http://www.poes-weather.com/~patrik/AO-51/ 3.6 mb
>>>
>>> Patrik
>>>
>>>> ----- Original Message ----- From: "Alexandru Csete"
>>>> <address@hidden>
>>>> To: <address@hidden>
>>>> Cc: <address@hidden>
>>>> Sent: Tuesday, December 08, 2009 3:57
>>>> Subject: Re: [Discuss-gnuradio] AO-51 and GRC
>>>>
>>>>
>>>> 2009/12/8 Craig Kief <address@hidden>
>>>>>
>>>>> I need a little help. I want to do a project involving GRC. There is a
>>>>> satellite called AO-51 (http://www.amsat.org/amsat-new/echo/). If you
>>>>>
>>>>> watch some of the youtube videos you will see what most folks are using
>>>>> this satellite for. It is great for using HAM licenses to do
>>>>>
>>>>> audio repeaters. I want to do this
>>>>> (http://www.youtube.com/watch?v=1HfvmU_utI8) with SDR. We have our
>>>>> ground
>>>>> station set up where we use nova software to drive our G5500
>>>>>
>>>>> rotators. We have a 144MHz antenna for TX and a 2.4GHz antenna for
>>>>> receive. We have a USRP-1 with a BasicTX and DBSRX for transmit and
>>>>> receive.
>>>>> We are using
>>>>>
>>>>> the GRC for our design work. What I want to do is be able to talk
>>>>> through
>>>>> a microphone and listen with a pc speaker on the
>>>>>
>>>>> rx side. My problem is that I am very new to GRC and am not positive
>>>>> about what blocks to use and what settings I should choose.
>>>>>
>>>>> Has anyone ever tried to do anything with AO-51 and GRC?
>>>>>
>>>>> Craig
>>>>
>>>> Hi Craig,
>>>>
>>>> I'm playing with GNU Radio and USRP for using it as ham radio
>>>> transceiver, though I'm still learning.
>>>>
>>>> Since AO-51 is an FM satellite it is relatively easy to have a quick
>>>> prototype up and running because there are already FM modulator and
>>>> demodulator blocks available in GNU Radio and GRC. There are even
>>>> examples for how to make FM transmitter and receiver in
>>>> /usr/share/gnuradio/examples/usrp/ or
>>>> /usr/share/gnuradio/examples/grc/usrp/ for GRC. For GRC I can only
>>>> find wide band FM receiver example, but you can simply replace the
>>>> wide band FM demodulator block with a narrow FM demodulator.
>>>>
>>>> I don't know how good DBSRX is above 2.4 GHz, I have only used it on
>>>> 2.2 GHz where it works very well. Otherwise there is the RFX2400 for
>>>> 2.3-2.9 GHz. Note the AO-51 is very often in V/U mode, i.e. uplink on
>>>> 145 MHz and downlink on 435 MHz and the DBSRX will not cover that.
>>>>
>>>> Cheers
>>>>
>>>> Alex
>>>>
>>>>
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>>>
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>>>
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