Monday, November 13, 2023

RTL-SDR V4 compared to RTL-SDR V3

HVDN prime author Steve K2GOG received two of the RTL-SDR V4 during its initial production run. 

Here we are about four months later and there have been many other reviews focused on basic differences between the two devices. 

There have also been impressively fast integration of the new drivers along with popular software. By mid September, almost everything was solved but I waited a while to do this article now that production has resumed and the V4 is easily found again until the R828T chips run out.

Almost every video or article focuses on the same things like which one works better for HF reception or other pretty basic things. There are some major differences where the V4 really shines and that is what this review is about.  Our goal is to NOT focus on the same thing and to not try to force our readers to buy one over the other, unless the below is of interest to you.

Please note, get the right antennae for what you want to do. Using telescoping crap antenna is not going to work well for almost everything we cover below based partially on the spectrum coverage chart below.

Directly from the "RTL-SDR Blog V4 Dongle Initial Release" article, there are some major things to point out.

  • 0-30 MHz Spectrum:  This has been beaten to death already. The V4 is much better at HF reception compared to the V3, but you still need to have a real antenna. Do not take shortcuts here as a marginal 2-3 foot (1m) telescoping whip is not going to impress you.  A major benefit is not having to select Q branch to receive the "short wave" spectrum, so with the right software the overall user experience is still better here.   It is worth noting that comparing the V4 to even the inexpensive "knock off" SDRPlay devices for around the same price still offers better HF spectrum coverage along with wider 10 MHz bandwidth compared to the V4's 3.2 MHz bandwidth.  Its time to move on. The RTL-SDR is fine for what it is and stop focusing just on this spectrum as a selling point.
  • 100-300 MHz Spectrum:  There are spots where coverage is slightly better with the V4 compared to the V3. Its not worth getting into much detail here, but the built in triplexer and filtering does a better job limiting out of band broadcast interference from the 88-108 MHz range, especially if you are interested in civilian aviation VHF 118-136 coverage as well as other amateur or utility communications.
  • 315 & 433 MHz ISM Spectrum:  If you really want to explore what is around you or wish to think you are some sort of "hacker" having better sensitivity and filtering around the 315 MHz range used for tire pressure monitors found on many vehicles in North America and the shared 433 MHz ISM range with many "Internet of Things" devices and amateur radio things is a huge gain here.  This was worth the expense for these monitoring target applications.
  • 868 & 915 MHz Sub GHz Spectrum:  Another area of improvement with the V4 device.  Many IoT devices worth sniffing around exist here. While the V4 does seem as if it is not as sensitive compared to the V3, I feel this is not too bad since it forces the user to use more purpose drive antennae to make up for the difference. 
  • >1000 MHz+ Spectrum:   North of 1 GHz, performance is not really that bad with the V4 and with an LNA, better antennae or combination of the two is fine.  Over time, the two V4 devices have been tested to have slightly less thermal drift and lower power consumption compared to the V3.  In many cases where monitoring L Band spectrum, this becomes important since the RTL-SDR's have been installed in areas not very accessible or have had to contend with heat build up.   For applications like HRPT satellites,  ADS-B, and so many other things found in the 1000-2000 MHz slice, the V4 has really been great when uses with purpose focused antennae.

Lazy Summary

We are talking about an under $40 USD device. Stop being cheap. Stop pretending this will be the best radio receiver ever made. Stop using crap antennae and blaming the SDR or the software. Stop thinking the world revolves only around HF spectrum.  Buy an RTL-SDR V4 if you are interested in doing many things which will motivate you to explore better antennae and software where you can find really cool things in the airwaves that may just be data signals and not just human voice communications.

Other Things

I really like the indicator light for when the bias T power is active. The L band patch made by RTL-SDR has an indicator, but its inside the antennae housing so is not viewable. Knowing the small green light on the V4 is on, does help ensure I know the antenna downstream is seeing power has been helpful Many software packages like SDRangel allows control of the bias T power, but a physical indicator is still nice.

Overall design in such a small package is hard to do.  We may be at the limits of what else can be done in this formfactor but with thermal management becoming more challenging, its commendable how the power supply has been redesigned. Earlier SDR suffered greatly from power issues, this is not the case with the V4.

If there were two front end major changes, I would love to have a built in dedicated high isolation filter which pretty much knocks out the entire 88-108 MHz range up to 60db since strong signals tend to mix at odd places at times or have a tight filter around 400 MHz for better ISM or radiosonde monitoring between 400-450 MHz.   Otherwise I am just picking on things I can solve other ways via outboard filtering or mission specific antennae with usually do a great job at out of band attenuation.

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