New Software Defined Radio Adventures with the RTL-SDR V4
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RTL-SDR is announcing the release of the RTL-SDR Blog V4 dongle based on the R828D tuner chip
The V4 comes with several improvements and changes:
- Improved HF Reception. Now uses a built in upconverter instead of using a direct sampling circuit. This means no more Nyquist folding of signals around 14.4 MHz, improved sensitivity, and adjustable gain on HF.
- Improved filtering. The V4 makes use of the R828D tuner chip, which has three inputs. We triplex the SMA input into three bands, HF, VHF and UHF. This provides some isolation between the three bands, meaning out of band interference from strong broadcast stations is less likely to cause desensitization or imaging.
- Improved Filtering x2. In addition to the triplexing, we are also making use of the open drain pin on the R828D, which allows us to add simple notch filters for common interference bands such as broadcast AM, broadcast FM and the DAB bands. These only attenuate by a few dB, but may still help.
- Improved phase noise on strong signals. Due to an improved power supply design, phase noise from power supply noise has been significantly reduced.
- Less heat. Due to the improved power supply design the V4 uses slightly less current and generates slightly less heat compared to the V3.
- Cheaper price! The price of the R860 chip which is used in the V3 and most other RTL-SDR brands increased significantly at the beginning of 2023 which is part of the reason as to why RTL-SDR dongles have been increasing in price recently. For the V4 we are making use of an existing stockpile of R828D chips which are now priced cheaper than new productions of the R860. In a time when high inflation keeps pushing prices up this is incredibly welcome.
The core change on the RTL-SDR Blog V4 design is the change from the R860 tuner chip to the R828D tuner chip. The R828D was previously a more expensive chip.
The R828D is very similar to the R820/R860 and shares much of the same circuitry. However, instead of just one input, it comes with three switchable inputs. RTL-SDR used these three inputs together with a triplexer to create a dongle with some extra input filtering.
The HF design consists of a SA612 double-balanced mixer circuit with front end filtering, which is connected to the 28.8 MHz oscillator that is also used for the tuner and RTL2832U chip. This means that HF frequencies are upconverted by 28.8 MHz. The drivers handle this upconversion seamlessly, so you just need to tune to 0 – 28.8 MHz in order to receive HF. There is no need to set any offset.
More information at https://www.rtl-sdr.com/
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