Original Blog V4 Dongle Based on R828D Tuner Chip (Main Unit with Aluminum Case) for RTL-SDR

Original Blog V4 Dongle Based on R828D Tuner Chip (Main Unit with Aluminum Case) for RTL-SDR

Description:
The V4 comes with several improvements and changes that are listed below.
* 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. Like the V3, the lower tuning range remains at 500 kHz and very strong reception may still require front end attenuation/filtering.
* 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.

There are some other minor changes including a new bias tee LED and a small cutout hole in the enclosure so it's easy to tell when the bias tee is on.

Of course the same innovations that we brought in with the V3 are still implemented such as the sleek conductive black metal enclosure which works as a shield and doubles as a heatsink, a thermal pad to sink heat away from the PCB, 1PPM TCXO, SMA connector, USB noise choking and improved ESD protection.

The V4 however does come with some disadvantages compared to the V3 that need to be noted:
* Due to the increased filtering there can be an average of 2-3 dB less sensitivity on some bands.
* The V4 requires the use of Blog drivers for RTL-SDR. Blog drivers for RTL-SDR are on GitHub. Please be sure to follow the installation instructions on the quickstart guide carefully. In most cases using our drivers simply means running our install-rtlsdr-blog.bat file, or replacing a dll file. (UPDATE: The default Osmocom branch now supports the Blog V4 for RTL-SDR, as does most other software)

More About the V4 Design:
The R828D
* The core change on the Blog V4 design is the change from the R860 tuner chip to the R828D tuner chip. The R828D was previously a more expensive chip, however with the huge price increases on the R860 which came in effect at the beginning of the year we have decided to make use of existing R828D stock which is now cheaper than the R860.
* 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. We have used these three inputs together with a triplexer to create a dongle with some extra input filtering. In the past there have been some R828D based dongles on the market, but all designs are based on TV receiver circuits. Because our design is different, you will need to use our Blog driver branch for RTL-SDR which has added compatibility for our R828D design.

HF Design
* 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. Our 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.
* An upconverter design also means that unlike direct sampling full gain control is available, and also there is no folding of signals across 14.4 MHz due to Nyquist.

Adding Basic Input Filtering
* One of the main problems with dongles for RTL-SDR is overload from strong broadcast stations such as broadcast FM, broadcast AM and DAB. By using a triplexer circuit we can make use of the three inputs on the R828D tuner chip to provide some filtering. The triplexer splits the input signal into HF (0-28 MHz), VHF (28 MHz-250 MHz), and UHF+ (250 MHz-1.766 GHz). This means that interference from something like strong broadcast FM at 88-108 MHz is more isolated when we are tuned to the HF and UHF bands.
* We've also made use of the open drain pin on the R828D (which does not exist on the R860) to implement a simple switchable notch filter for the main problem broadcast bands. These notch filters cover broadcast AM, broadcast FM and DAB, and reduce them about an additional 5-10 dB. By default the notch turns ON when tuned out of these bands, and is turned OFF when tuned within them.
* In terms of sensitivity, the disadvantage of adding more filtering is that it can reduce sensitivity in some bands. However, sensitivity for the RTL-SDR is usually not a problem in most situations, as we're usually limited by desensitization from strong out of band signals as mentioned above. If sensitivity is a priority an LNA such as our wideband LNA should be used anyway, for any RTL-SDR brand or model. Any front end LNA will totally dominate the sensitivity figures, making any sensitivity measurements of itself irrelevant (for RTL-SDR).

Revised Power Design
* The revised power design makes use of a more modern LDO with significantly better power supply noise rejection which results in much lower phase noise seen on strong narrow signals. There are also some PCB tweaks to reduce internally produced noise. The LDO improvement also has the effect of reducing power usage and lowering heat.

Other Changes
* We've also added an LED to the bias tee, so it's easier to tell if it has been activated in software.

Package Included:
* 1 x Main Unit with Aluminum Case

Packaging Details:
* Weight: 0.25kg