SDR# Insensitive receivers

[scanmanmi]

My portable FM radio picks up lots of stations but my USB SDR doesn't. The noise floor is always about -60. When I set the gain to 30dB I can pick up a little. I bought a second one and it does the same thing. I reinstalled the drivers and software. Any thoughts? What are the levels on yours and how does it compare to a portable radio?

 

[boatbod]

My portable FM radio picks up lots of stations but my USB SDR doesn't. The noise floor is always about -60. When I set the gain to 30dB I can pick up a little. I bought a second one and it does the same thing. I reinstalled the drivers and software. Any thoughts? What are the levels on yours and how does it compare to a portable radio?

What are you using for an antenna?
Broadcast FM uses high powered transmitters whereas most things that sdr users are interested in are much lower power.

 

[simpilo]

My portable FM radio picks up lots of stations but my USB SDR doesn't. The noise floor is always about -60. When I set the gain to 30dB I can pick up a little. I bought a second one and it does the same thing. I reinstalled the drivers and software. Any thoughts? What are the levels on yours and how does it compare to a portable radio?

If you're talking about the FM Broadcast band turn down the RF Gain or untick the auto gain. Manually adjust. Don't use high gain settings on FM Broadcast band. What you're seeing is noise from the computer and its (RTL-SDR) internal power supply. Adjust for like -125dbm noise floor and use a 30 inch long antenna. A set of TV rabbit ears with 50 ohm coax with a SMA connector will be fine if both telescoping whips are 30 inches making it a half wave dipole at 100MHZ. LNA4ALL in line will further improve it. Amplified rabbit ears might even work but it'll be a pure 75ohm impedance. Makes sure your SDR software is set for 192khz audio bandwidth.

 

[Ubbe]

SDR# are coded for one specific series of receivers and other generic dongle types will display differently. My RTL-SDR dongles have a noise floor of -50dBm in SDR# with a gain set to 40dB. It doesn't mean that the noise floor actually are -50dBm, it's something like -110dBm but the information from the dongle doesn't correspond with what SDR# are anticipating as the hardware are totally different. Automatic gain for both RF and IF works perfect to use with FM broadcast, it's what the dongle are designed for.

/Ubbe

 

[scanmanmi]

I guess my question is why can't these things work as good as a garage sale portable radio? Are there additional considerations? How do I know I didn't get stuck did two duds?

 

[hardsuit]

scanmanmi - most SDR are from HDTV and DVB-T broadcasting , the FM is usually CUT out or Attenuated at the Chip Level.
this is because FM radio can Interfeer with most SDR. you will have to Research which ones are a TRUE Wideband SDR and not a Repackaged HDTV Receiver. for Example ICOM has both a Wideband Radio Board and a Wideband SDR as well, no Compromises here as the ICOM does Everything from HF to AM-FM Radio to VHF/UHF and all the way to 3.4 Ghz.

 

[DRL-XM43]

Commercial FM using SDR# works great for me these are the settings I use.

 

[poltergeisty]

You're not adjusting the settings correctly. Look at that screen shot and try those settings.

SDRs are not a dial in a freq. and expect results. You have to make an effort to get what you want correctly though modulation type, bandwidth and step size, etc.

What software are you using?

 

[Ubbe]

A portable radio will always be better than a $10 USB receiver as it uses more filtering. FM broadcast uses +/-75KHz modulation so 150.000 are the correct setting with 100KHz step, but it doesn't matter much. Stronger signals will interfere with weaker stations much more in a USB dongle than a proper FM radio. At my place I can hear all local stations but distant stations are very weak or totally absent compared to the tuner in my living room stereo.

/Ubbe

 

[slicerwizard]

It has far less to do with filtering and much more to do with dynamic range. Dynamic range on dongles (all of them) is pitiful.

 

[iMONITOR]

Bob Grove & Bob Parnass (Monitoring Times), used to discuss the importance of dynamic range with scanners and how the manufactures didn't seem to be too concerned with it back in the 70's - 80's. All the birdies were overwhelming!

 

[Ubbe]

All the birdies were overwhelming!

Yes, but birdies, the often high pitched beat tone of two frequencies mixing, relate to internal oscillators and multiples from unpure signals in the electronics and only fix where to lock out the affected frequencies. In professional radios you could often activate clock shift on a channel that slightly detuned an oscillator enough to move a birdie to other frequencies.

/Ubbe

 

[simpilo]

My portable FM radio picks up lots of stations but my USB SDR doesn't. The noise floor is always about -60. When I set the gain to 30dB I can pick up a little. I bought a second one and it does the same thing. I reinstalled the drivers and software. Any thoughts? What are the levels on yours and how does it compare to a portable radio?

The antenna that is shipped with the Nooelec brand needs a ample ground plane. I use coffee can tins. The RTL-SDR Blog dongles ships with antennas in the dipole configuration. Like rabbit ears sorta. They had the groundplane in mind. Both elements need to match in length. Tuned to 1/4 wavelength.

I can decode a P25 trunked channel with mine that is around 15-20 miles away. Hear NOAA weather radio 60 miles away on a good day. Local weather radio is 25 S-Units (measured by HDSDR's relative signal meter). I use a dipole configuration 18 inches on both legs for 160MHZ. Might try it.

-60dbm noise floor is high. Mine sits around -100dbm on VHF, -115dbm 460MHZ, -124dbm 850MHZ. Might want to move that dongle away from the computer because some computers spit out a ton of noise which will block alot of signal. Try about 20ft of USB extension cable. Not the Walmart stuff. From Amazon. Take your pick:
Amazon.com: usb extension cable - 15 to 24.9 Feet / Cables & Interconnects / Computer Access...: Electronics

 

[iMONITOR]

The antenna that is shipped with the Nooelec brand needs a ample ground plane. I use coffee can tins. The RTL-SDR Blog dongles ships with antennas in the dipole configuration. Like rabbit ears sorta. They had the groundplane in mind. Both elements need to match in length. Tuned to 1/4 wavelength.

I can decode a P25 trunked channel with mine that is around 15-20 miles away. Hear NOAA weather radio 60 miles away on a good day. Local weather radio is 25 S-Units (measured by HDSDR's relative signal meter). I use a dipole configuration 18 inches on both legs for 160MHZ. Might try it.

-60dbm noise floor is high. Mine sits around -100dbm on VHF, -115dbm 460MHZ, -124dbm 850MHZ. Might want to move that dongle away from the computer because some computers spit out a ton of noise which will block alot of signal. Try about 20ft of USB extension cable. Not the Walmart stuff. From Amazon. Take your pick:
Amazon.com: usb extension cable - 15 to 24.9 Feet / Cables & Interconnects / Computer Access...: Electronics

USB cables with ferrite chokes.

 

[simpilo]

USB cables with ferrite chokes.

Then how many and what spacing between the chokes along the cable and what size? Ferrite chokes come in different sizes. Which is best? I don't mention chokes. I never saw any benefit on VHF and UHF. Possibly a benefit for HF.

 

[iMONITOR]

Then how many and what spacing between the chokes along the cable and what size? Ferrite chokes come in different sizes. Which is best? I don't mention chokes. I never saw any benefit on VHF and UHF. Possibly a benefit for HF.

Uniden uses ferrite chokes on their USB cables.

 

[Ubbe]

I get noticable interferences on HI-VHF with bad USB cables without any ferrites. The local nick nack store that sells elecronics have clip on ferrites that says it covers 30MHz-600Mhz, so there are different ones so be sure to check the specifications. Set them at the both ends of the cable and if possible have the cable go two or more turns in the ferrite as each turn will add to the attenuation of the interference, or add several ferrites if interferencies are still detetcable. LAN cables are also interference prone and video cables to a computer screen as well as any other cable like those for audio that could work as transmit antennas.

/Ubbe

 

[simpilo]

I just know what I see. I see 850-860MHZ noise free without chokes. Indoor antenna will see anything interfering anyway so it is futile to add chokes. Interference like computer noise will always be in the way. VHF seems worst plagued. Move RTL-SDR away from noise problems.

 

[DRL-XM43]

I'm in a basement (worst possible case) with the simplest of telescoping antennas and can haul in all the regional signals with no problem, commercial FM booms in as do various trunked systems adsb and all manner of other stuff.

I use Nooelec smart dongles.

 

[simpilo]

I'm in a basement (worst possible case) with the simplest of telescoping antennas and can haul in all the regional signals with no problem, commercial FM booms in as do various trunked systems adsb and all manner of other stuff.

I use Nooelec smart dongles.

I guess some get a dongle out of a bad batch from the factory. I haven't a issue with reception with my Nooelec Smart.