I currently own two NooElec RTL2832 + R820T2 SDR's that I use for spectrum scanning, and to trunk scan my local public safety radio calls that are always broadcasting (police, ambulance, fire, transit calls). I'll post more about that in a separate topic though.
The RTL-SDR stands for Realtek-Software Defined Radio because it is based on the Realtek RTL2832U chipset. These are very cheap $20 devices that can be used as a computer based radio scanner. More can be read about them here: http://www.rtl-sdr.com/about-rtl-sdr/
These devices are however vulnerable to RF noises/interference, which can affect the noise floor and receiving capability of remote signals. The screenshot shown above was my SDR receiving signals in VHF, around the 130-140 MHz band. The noise floor was seen to be around -40dB.
A user named will1384 on reddit has put together a gallery of test results that he obtained after trying different methods of RFI shielding:
Image gallery + his findings:
One of his methods was using a blue anodized aluminum enclosure like this one off eBay:
...so I bought two of these enclosures to see if it would have any effect. However, as he shows in his imgur gallery, I decided not to ground the USB PCB connection to the case like he did.
|eBay aluminum enclosure and RTL-SDR casing taken off|
|Measured out where to drill a hole for the MCX connection on the SDR to fit|
|SDR was slid and snapped into place afterwards|
|One of the side plates needed to have a cutout for the USB to stick out|
|Hooked up to PC along with an antenna for each SDR|
|NooElec SDR in OEM plastic casing. Noise floor: around -40dB|
|NooElec SDR in blue aluminum enclosure. Noise floor: around -42.5dB|
Although not too obvious, the noise floor did seem to drop by a few decibels. To improve my reception in the future, I plan to purchase a set of LNA's (low-noise amplifiers) to help pick up farther away radio signals.Learn more »