SDR (Software Defined Radio) For Satellite (1 Viewer)

Balock

SatelliteGuys Pro
Pub Member / Supporter
Lifetime Supporter
May 4, 2006
624
71
Beebe, AR
The two software apps I've used so far have been SDR# and HDSDR, running on an HP AMD Athlon II X4 Quad-Core processor desktop system at 3GHz under Windows 7 Home Premium--no problems unless I have something else running that also hogs the CPU. Both of these apps can use a lot of CPU for both processing the signal and running the display (there's a lot of math involved!). I've read that some dual-core systems that are optimized/marketed more for gaming may work ok with SDR software (faster cpu/graphics).

You can try adjusting the sample rate in the RTL-SDR settings in SDR#. The default is 2.4 MSPS (mega-samples per second) and can go as low as .25 MSPS. The lower the sample rate, the lower the CPU usage but you also will loose audio quality as you lower the sample rate. Also, the FFT resolution can be adjusted in the menu bar under the FFT section...the smaller the value, the less detailed the signal display (and the quicker it reacts). This option won't affect the audio quality, tho...only the display. You may be able to adjust both options enough that you can get rid of the audio dropouts and keep the system fairly responsive. Of course, you can always get a faster computer ;)

Good luck!
 

cypherstream

SatelliteGuys Pro
Jul 6, 2010
600
59
PA
Just purchased a NooElec R820T2 dongle. I'm running the SDRSharp software. Just hooked up the dongle last night. Haven't done much exploring yet. I tested the setup on the standard wideband FM stations. There are dropouts in the FM audio and the display video is sometimes slow to react to mouse movements. I'm guessing my old laptop doesn't have the 'horsepower' for the software. Is my theory correct about the laptop? Any other software that might work better with my current computer?

Laptop Specs:
2.2 GHz Intel dual core
64k primary cache
2048k secondary cache
3964 Megs useable memory
(Win 7 Home Premium)


What do you have your sample rate set to? I find anything higher than 2.56 MSPS is unusable on a core2duo with 4gig ram on Windows 8.1. My sampling mode is Quadrature sampling at 2.56 MSPS. You'd think higher would be better but its just overkill.
 

Cosmo Blatz

SatelliteGuys Pro
Jun 13, 2014
544
419
S.E. WI and Central NV
Thank you Balock and cypherstream for your replies. I cut the sample rate down to .25 MSPS, turned off the waterfall, and lowered the FFT resolution. According to Windows Task Manager, SDR# is still using about 70% of the system resources.
However, SDR# is now usable with good audio! Thank you both for your help. Researching new computers...
 

Cosmo Blatz

SatelliteGuys Pro
Jun 13, 2014
544
419
S.E. WI and Central NV
Thank you Balock and cypherstream for your replies. I cut the sample rate down to .25 MSPS, turned off the waterfall, and lowered the FFT resolution. According to Windows Task Manager, SR D# is still using about 70% of the system resources.
However, SDR# is now usable with good audio! Thank you both for your help. Researching new computers...
 

spongella

SatelliteGuys Pro
Pub Member / Supporter
May 12, 2012
1,578
1,165
Central NJ
Great posts, guys. This morning I tried a few things with the dongle-spectrum analyzer from NutsAboutNets. I have a stationary dish aimed at Telstar 15W with about 40% signal quality. Both TPAI and TVGE come in well on my FortecStar Dynamic receiver. The parameters for this TP are 11964/v/14734 as per my STB. So, did some calculations: 11964 (downlink frequency) - 10600 (LO frequency) = 1364 MHz IF. That frequency is within the receiving range of the dongle. So far so good.

Now, since the 10600 LO frequency is selected to receive this broadcast that means that a 22 KHz signal is being sent by the STB. Have to keep that in mind.

Next, removed the RG/6 cable from the STB and hooked it into a Channel Master CM-1007A satellite finder. This powers the LNB and also allows you to change polarization and LO frequencies. So I set the meter on 13v (vertical polariz) and turned on the 22 KHz tone to select the 10600 LO (am using a Universal LNB 9750/10600). Then, attached the dongle to the output of the meter and scanned 1300 - 1400 MHz. See pic below. Not too encouraging, but there appears to be a wide flat peak between 1359 and 1372 MHz. The center would be around 1364 MHz. If you add the LO frequency of 10600 to that it would be around 11964, the downlink frequency for TPAI/TVGE.

I could be way off base here. But just to confirm, I shut off the 22 KHz tone and the peak disappeared. See next pic.

Last thing done was to start up HDSDR and look at what 1364 MHz is like on the dongle alone. See pic. Don't know how to interpret this, but definitely shows some transmissions on this frequency. Many narrow band signals. (See third pic). And if you tune below 1350 MHz or above 1372 MHz the signal slowly disappears. So this transponder signal appears to be about 22 MHz wide. Again, just to be sure it was a legit signal, I turned off the 22 KHz signal and the waterfall went blank - see fourth pic which shows upper half of waterfall (22 KHz on) and lower half of waterfall (0 KHz).

Next step, if this all makes sense ( I defer to the wisdom of those on the forum who are more experienced) will be to scan different areas using both LO's to see what other signals are on the bird. Not for any nefarious use, just in pursuit of knowledge. Feel free to shoot these ideas down as I could use the help of more knowledgeable folks on the forum. Thanks.

Sponge
 

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Titanium

AI6US
Lifetime Supporter
May 23, 2013
7,095
7,950
Meadow Vista, Northern California
11964 is a QPSK with a symbol rate of 14714. That carrier appears to be about that wide. Notice the large carrier below? That carrier is TP frequency 11920, a 8psk with a symbol rate of 45000. You should note that that carrier extends down to approximately 11895MHz. The carrier to the right is probably a feed as TP frequency 12044, a 8psk has a symbol rate of 45000 and the low freqency of the carrier would be around 12020 (above the current frequency range of the spectrum scan).

You are testing exactly right:
  • Scanning 950 - 1950 with the 22KHz off and 13Vdc LNB power will cover 10.7GHz - 11.7GHz vertical polarity.
  • 950 - 1950 with the 22KHz off and 18Vdc LNB power will cover 10.7GHz - 11.7GHz horizontal polarity.
  • 22KHz on and 13Vdc scan 950 - 1950 will cover 11.7 - 12.7GHz vertical polarity.
  • 22KHz on and 18Vdc scan 950 - 1950 will cover 11.7 - 12.7GHz horizontal polarity.
The carriers have digital data with an embedded transport stream.
 

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