Terratec RTL SDR Dongle – Part 1

In 2012, I built a Softrock SDR kit, but did not do much with it, except study its schematic and played with the Rocky program.

About 2 months ago, an article in the July issue of the Spectrum caught my eye.

IEEE_spectrum01color

I have scanned the article, and you can read it here.

At $30 Singapore dollars on Ebay, it was worth a try. A typical Ebay listing looks like this.

Ebay_RTLStick02There are several good resource sites for hams who want to use the device as an SDR. One of them is RTL_SDR.

Two tuner chips you will usually find in these DVB-T dongles are the Elonics E4000 and the Rafael Micro R820T. The Elonics is from a UK Manufacturer while the Rafael part is from Taiwan.

I was interested in what the input impedance was like. The first place I turned to was the Elonics E4000 datasheet. This datasheet is freely available, unlike the RTL2832 DVB-T demodulator.

Elonics_S11_table Excerpts from the Elonics datasheet

Elonics_S11_Graph

Here are the Elonics E4000 and the Rafael Micro R820T datasheets.

Initially, I did not want to modify the dongle PCB, so I made an input adapter to connect to the SMA test cable of my Agilent E5061B Network Analyzer

A04_6727  Input adapter

Terratec_Adaptor_SWR

Terratec_Adaptor_RetLoss

I wasn’t sure that what I was measuring was the input adapter or the actual input impedance, so I decided to get in closer. As the network analyzer was calibrated at the end of the SMA test cable, it made sense to replace the input connector of the dongle with an SMA.

A04_6749  Original input connector removed…

A04_6759  … and replaced with an SMA.

You can’t get closer to the chip than that, without removing the input protection diode network. You can see where the protection network is connected by examining the Elonics application schematic. I guess the dongle’s input circuit would not not be much different.

Here are the test results, and they look pretty similar to those obtained with the input adapter.

Terratec_SMA_RL_SWR

Terratec_SMA_smith

Here are some further work which I would like to do and publish here:

a.  Measure the input impedance of a R820T based dongle

b. Measure input sensitivities of both the Elonics E4000 and R820T based dongles.

Thanks for visiting,

73 de Jeff 9V1AS

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One thought on “Terratec RTL SDR Dongle – Part 1

  1. Pingback: SARTS Talk Oct 2013: SDR Basics by Min Than 9V1XY and Jeff 9V1AS | Jeff Yeo 9V1AS

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