In this post we take a closer look at two popular SDR dongles – the RTL-SDR and NESDR Smart v4. We will explain the differences between the two and make recommendations on which one to buy.
The RTL-SDR is one of the most popular SDRs on the market today. In fact it is our top SDR pick for those looking to get started with SDR on a tight budget.
The NESDR Smart v4 is based on the same chipset, namely the RTL2832U. As a result, internally they feature the same radio receiver technology. These two SDRs are able to receive signals in the frequency range of 25 MHz to 1750 MHz. Also, their performance specifications in this frequency range is identical.
What’s the difference between the RTL-SDR and the NESDR?
There are a few main differences. Without further ado, let’s get right into the details:
DIMENSIONS
The NESDR is narrower than the RTL-SDR. This means that you can insert NESDR’s into the USB ports of the Raspberry Pi side-by-side. You can’t do that with the RTL-SDR.
So is that an issue?
Not really. In fact we recommend not to plug the SDRs into the USB ports directly. There are a couple of reasons for that.
Firstly, any RF noise from the laptop or Raspberry Pi will get picked up by the antenna and show up in the output of the SDR. This is something that is very undesirable. Our recommendation is to use a USB cable to physically separate the USB dongle from the laptop. And in that case, the wider RTL-SDR is not an issue.
Secondly, if you drop your laptop with a USB dongle attached, it will stress the USB port and potentially damage it.
CLOCK OSCILLATOR
The NESDR has a TCXO (Temperature controlled crystal oscillator) has an accuracy of 0.5 ppm (parts per million), while the RTL-SDR has an accuracy of 1 ppm. What does this mean and what’s the impact?
Let’s say you tune to a frequency of 1 GHz with both SDRs. With the NESDR, there will be a frequency error of up to 500 Hz. In the case of the RTL-SDR, the frequency error can be as high as 1000 Hz or 1 kHz. This means that the signal you’re monitoring can be offset from where you’re tuned to. If you’re trying to detect and/or demodulate the signal, this will result in errors.
DIRECT-SAMPLING MODE
The frequency range of the tuners used in the RTL-SDR and NESDR is 25 MHz to 1750 MHz.
The RTL-SDR implements a direct sampling mode whereby signals at the RF input can be fed directly to the analog-to-digital converter (ADC). This means that you can view signals in the range of 500 kHz to 28 MHz.
Here is a video that shows High Frequency or Medium Wave AM broadcast radio being received with the RTL SDR.
It’s important to point out here that the performance of the RTL-SDR in this direct sampling mode and frequency range below 28 MHz is not as good as performance in the range 25 MHz to 1750 MHz. In fact the team at Nooelec recommends the use of the Ham It Up RF Upconverter for viewing signals below 28 MHz.
BIAS TEE
The RTL-SDR has a built-in bias tee that can be enabled by software. It provides 4.5 volt and up to 180 mA of current. We have covered Bias Tees in this post previously. A bias tee allows you to power a remote low noise amplifier – for instance, one that is mounted close to the antenna on the top of a tower.
Conclusion
In this post we have looked at both the RTL-SDR and the NESDR from Nooelec. The main differences between the two are captured in the table below.
| NESDR | RTL-SDR | |
| Dimensions | 3.54 x 0.39 x 0.39 inches | 5.12 x 2.56 x 0.43 inches |
| TCXO accuracy | 0.5 ppm | 1 ppm |
| Direct Sampling | No | Yes |
| Bias Tee | No | Yes |
If you are looking for a low budget SDR that goes down to 500 kHz for HF monitoring the RTL-SDR is the one you should buy. Or if a bias tee is required for remote operation – once again, the RTL-SDR should be your pick.
However, if you’re looking for better frequency accuracy although with a limited frequency range, buy the NESDR. If you want to monitor the entire frequency range down to 300 Hz we recommend buying the Ham It Up upconverter as well.
