I’ve played with these RTL-SDR sticks for several years now and I am still amazed about the possibilities I have with these cheap pieces of hardware. I managed to receive several data modes like ADS-B, ACARS, AIS and the wireless outdoor thermometer of my neighbor – I’ll write several follow-up posts on this topics 🙂
I decided to get two new Sticks for my collection – this time with a TCXO oscillator to get a more stable reception.
Modified Stick? Whats the deal?
A common problem for these sticks is frequency stability over time. As the oscillator is heating up under load, the frequency of the crystal measured in ppm (parts per million) will change – which causes the frequency to shift. Typical values for cheap sticks are +-150ppm. The real amount of frequency should could be several kHz, which make this behaviour really annoying for headless receivers (like ADSB receivers on a Raspberry Pi) – especially if you try to receive a narrow signal.
TCXO to the rescue
To get rid of this shift, a better, temperature compensated oscillator is needed as replacement for the standard crystal. Compared to a normal crystal oscillator (short XO), a TCXO is a temperature compensated (TC) crystal oscillator (XO). These TCXO have a stability of 1ppm compared to the +-150ppm of a uncompensated oscillator.
There are two problems you will encounter if you want to modify your RTL-SDR yourself. First problem ist the availability of the 28.8MHz TCXO you’ll need – hard to get if you don’t want to order > 1000pc from the factory. The second problem is the size. As you can see, the components you have to handle are really tiny. Fortunately, several companies have realised that need and offer modified sticks.
I ordered two modified sticks from two different sellers.
NooElec NESDR Mini 2+ 0.5PPM TCXO
Sellers description: This custom NooElec SDR is a modified DVB-T USB dongle tuned for SDR usage, including a high-accuracy, Japanese fabricated, GPS-rated 0.5PPM TCXO crystal, and improved capacitors and inductors compared to generic devices.
This stick comes with a simple antenna and a (quite useless) IR remote. The antenna connector is a MCX.
Cost: US$38.90 incl. shipping from US (Order here)
RTL-SDR Blog R820T2 RTL2832U 1PPM TCXO
Sellers description: Several improvements over generic brands including use of the R820T2 tuner, improved component tolerances, a 1 PPM temperature compensated oscillator (TCXO), SMA F connector, bias tee circuit and break out pads for easy direct sampling modification.
This comes with two (!) telescope antennas, a magnetic mount with 1m cable and a more convenient SMA F connector. The smaller antenna has a variable length from 6 to 20cm, the larger one a length 20 and 150cm.
Cost: $24.95 USD+ shipment from China (Order here)
The performance of both sticks is outstanding. The RTL-SDR-Blog stick is a perfect kit as you can adapt the antennas to the frequencies you want to receive.