Tagged: FC0013

Driver Patch for FC0013 RTL-SDRs Improves UHF and ADS-B Performance

Thank you to Benjamin Larsson for submitting news about a FC0013 tuner patch he's submitted for the Osmocom RTL-SDR driver code. FC0013 based RTL-SDRs have been relatively unpopular due to the reduced tuning range of only 22 - 1100 MHz, compared to the larger 24 - 1766 Mhz range provided by the R820T2 chip. However, they have been found in some cheaper units.

Benjamin's patch reportedly improves UHF performance above 862 MHz, and also seems to make ADS-B reception usable.

The patch was submitted to the Osmocom GitHub, however, this Git is not monitored as Osmocom have their own patch submission system via mailing list. But if you have a FC0013 dongle and want to try it, the entire change consists of only a single register value change which could easily be manually modified in the driver code before compilation. 

Register change to improve UHF performance on FC0013 RTL-SDR dongles.
Register change to improve UHF performance on FC0013 RTL-SDR dongles.

Comparison of several SDRs on degradation from nearby strong signals at broadcast FM frequencies

The programmer of Linrad (aka Leif sm5bsz) has uploaded a video to YouTube that compares several software defined radios on dynamic range and compression performance in the presence of strong nearby signals. In the video Leif tests the Airspy, BladeRF with B200, FDM-S1, Funcube Pro+, rtlsdr/E4000, rtlsdr/FC0013, rtlsdr/R820T, SDR-14 and SDRplay.

The main test works by tuning to a broadcast band FM frequency and then injecting a strong carrier signal at distances of 500 kHz, 1 MHz, 2 MHz and 5 MHz from the center frequency. The carrier signal strength is slowly increased until the SDR shows signs of complete degradation of reception of the FM signal. Better SDRs will tolerate stronger nearby signals without degradation.

The results are summarized at 34:20, 1:21:38 and 1:48:30. We have also taken screencaps of the results at 1:21:38 and 1:48:30 and they are shown below. The first column is when a higher gain is used, and the second column is when a lower but still barely copyable gain level is used. In the Levels for loss of performance columns smaller numbers are better and in the Dynamic range columns larger numbers are better. Finally, at the end of the video starting at 1:45:55 Leif also tests the spur performance of the SDRs.

Results at 500 kHz and 1 MHz Seperation
Results at 500 kHz and 1 MHz Seperation
Results at 2 MHz and 5 MHz Seperation
SDR on 88-108 FM part1

Review of Various Lesser Known RTL-SDR Dongles

While the standard R820T dongles are the cheapest, most popular and best overall performing, there are other lesser known dongles variants out there which contain RTL2832 chips. Gough Lui has reviewed two lesser known dongles with Belling Lee (PAL) connectors on his blog.

One dongle uses the FC0013 tuner, and the other uses the R820T chip. Gough opens the dongles up and inspects their electronics and gives his opinions on the design.

One of the alternative R280T models with PAL antenna connectors
One of the alternative R280T models with a PAL antenna connector

More Comparisons Between the E4000, R820T, FC0013 and Linrad and SDRSharp

A few days ago we posted a video by sm5bsz showing some comparisons between the E4000, R820T and FC0013 tuners, and also a comparison between the special linearity gain mode driver in Linrad and standard Osmocom driver in SDRSharp.

Now sm5bsz, programmer of Linrad and the special gain modes for the E4000 has done another test using only Linrad, which more fairly demonstrates the difference between the various tuners, and the effect of the special gain drivers in Linearity mode. He writes

In this video RTL2832 dongles are compared for sensitivity, spurs and intermodulation. The difference between the Linrad linearity mode and the original Osmocom gain setting is demonstrated as well as spurs in R820T and FC0013.
Which one to prefer depends on the local RF Environment and whether a selective filter is used between the antenna and the dongle.

Note: The Linrad vs SDRSharp video has been removed by the uploader.

Finally in this video, he also compares the standard Osmocom driver to the sensitivity mode available in the modified gain profile drivers. He writes

The sensitivity mode has very poor performance for signals far away from the passband, but it allows about 10 dB better dynamic range for interferences within the passband. Sensitivity mode is for usage with a selective preamplifier while the Osmocom gain mode is a reasonable compromise. The Linrad linearity gain mode is for use without filters in difficult RF Environments.

e4000 sensitivity mode

Linrad can be downloaded from here and the modified Osmocom drivers with linearity and sensitivity gain profiles for the E4000 can be downloaded here. SDRSharp can also use the modified Osmocom drivers with Linearity and Sensitivity modes with this plugin by Zefie.

Video Comparison Between E4000, R820T, FC0013 and Comparison with SDR# and Linrad

On YouTube sm5bsz has uploaded a video showing a comparison between the E4000, R820T and FC0013 tuners, and also comparing the receive performance of SDRSharp and Linrad. In the video Linrad showed superior receive performance with the E4000 when compared to SDRSharp due to some custom gain profiles which are enabled in Linrad only (but can also be enabled in SDRSharp with a plugin/mod).

Note that the reason Linrad showed better performance is purely due to the fact that he used a modified librtlsdr driver in Linrad which has the custom gain profiles. However, in a previous post we posted about a modification/plugin to SDRSharp which allows this modified librtlsdr to be used, which will allow SDRSharp to perform as well as Linrad for the E4000.

Linrad is another software defined radio program which is much more difficult to use, but was the first program to support the modified librtlsdr. Some people prefer Linrad due to it’s advanced GUI which has a lot of signal information on display.