SDR (Software Defined Radio) For Satellite

[Jim S.]

I haven't had a problem with the USB drivers getting lost lately, but for some reason I used to. Sometimes unplugging the devices would work, other times, I had to reboot Windows.

If you had the RTL AGC and tuner AGC buttons unchecked, did you try moving the tuner gain slider up from 0?

 

[Stargazer]

Yes, when I moved the tuner gain slider up from 0 I started receiving stations. I just thought that the noise floor of -50s db were a bit high and should have been more in the -80s to -100s unless the noise floor is much higher in that frequency range compared to wifi. The noise floor is high enough to where I cannot tell much difference between a signal coming in on the spectrum analyzer but I could see signal on the rainbow.

 

[Jim S.]

I have a high noise floor on mine too. I think it's the devices. They're intended for reception of broadcast signals, and presumably strong broadcast signals given the useless antennae they ship with, so there probably isn't a lot of decoupling of noise from the computer going on. And I don't know why professional engineers feel that it's appropriate to manufacture RF devices in plastic enclosures.

 

[Titanium]

50dB noise floor is quite high. On my DVB-T USB dongles using an outside discone, I see approx 60dB noise without any shielding or filtering on the dongle or USB power source. Judging from what I hear on my antique Arvin floor model AM radio, these computers and printers put out quite a bit of RF garbage.

For an experiment, I wrapped the DVB-T USB in foil and dropped the noise by about 3-5 dB. Will be permanently mounting the DVB-T and the NooElec HamItUp upconvertor PCB in a single shielded case with one connecting USB cable w/ferrite. See if that mod provides a better noise floor. Here are a few images captured on FM and Public Safety frequencies for comparison.


This first image shows a typical noise level centered near 88Mhz with RF gain at 0dB.


Second image is an average RF gain of 16 - 17dB to provide 30 - 35 FM carrier levels for good FM broadcast reception.


This image shows average RF gain of 25 - 30dB for Public Safety 159Mhz

 

[Joe DC]

Check my post 91 on how to calibrate the noise floor. You should end up with about -114dB depending on frequency.

 

[Conky]

has anybody done a comparison on which usb tuner has the best performance?

 

[Titanium]

Thank you Joe DC. Nice! Don't how I missed this or your previous #91 post.

Expanded range and accuracy!Great range and offset on the Spectrum display. My noise floor is now accurately displayed in the 115dB range for the FM band. Now I can see the spectrum..

Ever wonder what you are listening to or where to listen?

 

[Joe DC]

Your welcome. If anyone is interested this page goes into more detail and also shows how to calibrate frequency accuracy. I used an old crystal controlled walkie talkie with a dummy load for calibration.
http://forums.qrz.com/showthread.php?391657-RTL-2832u-R820T-SDR-as-a-Spectrum-Analyser

 

[Jim S.]

Expanded range and accuracy!Great range and offset on the Spectrum display. My noise floor is now accurately displayed in the 115dB range for the FM band. Now I can see the spectrum..

I'm confused. While I agree that a noise floor of -50 or -60 seems way too high, shifting it down to -115 puts my local 53kW FM station at only -60, which seems way too low. So I compromised, and moved the floor up to around -90.

 

[Stargazer]

I thought by moving the noise floor that it would not actually change what the noise floor was but just change what the chart would say unless the default setting is not the true noise floor? That is why I did not do it. I figured there were a lot of stations that would come in above the noise floor and not be able to receive them as a result.

 

[Titanium]

I may be interpreting something wrong, but as I understand.... The Sharp+ has a default setting for all DVB-T USB modules regardless of sensitivity. This configuration setting modifies this default to approximate the actual noise floor of the device without using calibration tools.

I have read and observed that above -30dBm the intermodulation starts becoming an issue. Reducing the gain will keep signals below this point and reduce the bogeys.

 

[radio]

May I demonstrate my embarrassing and complete lack of knowledge on this topic? We had a listener to our AM station FAR away from us,
who posted around Christmas that they received us much farther than "normal" radios would allow, and said it sounded good (see attach)

Is it possible these types of radios are able to go 'where no radios have gone before" in terms of DX for AM, and/or stereo AM?

I'm glad to have listeners ANY way we can, but Muskegon is a long haul from us, and on an SDR radio...I'm intrigued.
Guess I need "SDR" for dummies and to start reading!

 

[Titanium]

SDR is not miracle software, but it comes close! The listener doesn't say what tuner they are using with the SDR software, but it will play a major role. Like any RF listening device, the antenna remains the key component.

The DVB-T USB tuner sensitivity is average, but the ability to change the parameters with the SDR software helps pull out signals that might be lost with an average radio. For $16 it is an incredible device and by far, the best technology "investment value" that I have enjoyed for many years!

 

[Stargazer]

It says its not connected or driver is not working properly when I select RTL/SDR USB so now I cannot use the device at all. I have tried unplugging it from the usb port, reconnecting and restarting windows with no luck. I connected it up to my tablet but the only software that you can get on there they want 10.50 for it and I would hate to pay for something that I do not know is going to work for me or not. The demo version has no spectrum analyzer so I dont even know how you can try it out. I have other antennas to try out with this thing if I can get it to work again. I was looking forward to messing with noise floor adjustment and using my other antennas.

 

[wallyhts]

It says its not connected or driver is not working properly when I select RTL/SDR USB so now I cannot use the device at all. I have tried unplugging it from the usb port, reconnecting and restarting windows with no luck. I connected it up to my tablet but the only software that you can get on there they want 10.50 for it and I would hate to pay for something that I do not know is going to work for me or not. The demo version has no spectrum analyzer so I dont even know how you can try it out. I have other antennas to try out with this thing if I can get it to work again. I was looking forward to messing with noise floor adjustment and using my other antennas.

What OS?

 

[Titanium]

If windows, do you see device "Bulk-In, (Interface 0)? If not, the device driver is not installed.

If so, uninstall the driver and reinstall.

 

[KE4EST]

Got my all my cables in Yesterday. Now time to start playing with my converter!!

 

[KE4EST]

And it works beautifully! Listening to a guy right now in Europe on 20 Meters! :excited:

 

[Titanium]

My China superpack of MCX cables arrived Friday.

Bought a Hammond 1511 cast aluminum case at Fry's yesterday and will mill the ports for the upconvertor. Will leave space to probably eventually add the DVB-T tuner as well.

 

[KE4EST]

...and a whole group in California on 15 Meters.