[NLRS] First tests with DVB-T dongle

[Doug Reed]

A friend dropped off a couple RTL2832/E4000 DVB-T dongles today. The 
dongles are kind of generic. One is white, standard USB size, the other 
is a black square mini-dongle. No distinguishing features except they 
are both RTL2832 based.

The dongles are interesting because raw IQ data samples from the 
receiver chip can be routed to the USB port and captured by the computer 
for further processing. So with the proper software it becomes an SDR 
receiver that is good over the full range of the E4000 receiver chip. It 
will cover all the ham bands from 2M to 1.3GHz including most of the 
range from FM broadcast to GPS. This is well beyond the published range 
for the chip and seems to depend on actual component values in the dongle.

A lot of active development work is being done on the Ultra-Cheap-SDR 
Yahoo group. Based on my reading, there is a lot of different software 
packages that will work. But the easiest to get working (currently) 
seems to be the SDR# (SDR-Sharp) program using USB drivers from the 
ZADIG project. That is what I chose to do and it installed easily on two 
different laptops.

As expected from the install directions, the 1.4GHz Atom N270 CPU in the 
Mini-9 netbook is too slow to run cleanly, the audio skips because it 
can't keep up, but it did try to receive FM from 102.1MHz with the 
spectrum display and waterfall working. Both dongles worked. I didn't 
look closely at either one to know if one or the other was performing 
"better" for receive sensitivity.

I then installed on a HP Compaq 6710b laptop with a 2GHz Centrino 
Core-Duo CPU. Again, both dongles worked fine, this time including FM 
stereo audio with no drops or stutters while displaying the spectrum and 
waterfall. The waterfall makes it easy to see intermittent or weak 
signals. In the FM band, that isn't a real problem. I preferred to turn 
off the waterfall and get a larger spectrum display.

What I'd really like would be a "poor man's spectrum analyzer" type 
program for the dongle. Adding peak hold to the current spectrum display 
would go a long way toward what I want. Adding some secondary processing 
to act as a modulation analyzer would make this a wonderful tool for 
repeater owners and anyone else wanting cheap "test equipment."
The dynamic range is limited by the 8-bit ADC so there are some things 
it can't do but still one heck of a lot it could do....

OK, so now I have a $20 dongle that turns a 8 pound laptop into a $10 
transistor radio..... If it could replace a $1000 spectrum analyzer and 
provide some modulation analyzer functions, that would be a much better 
exchange ratio....

For simple signal reception, the SDR# (SDR-Sharp) program seems to do a 
good job on WFM anyway. It supports Fun Cube, RTL2832, and SoftRock 
hardware devices and multiple modes with WBFM, NBFM, AM, SSB, CW as 
standard options. I haven't tried to find any narrow band FM or aircraft 
signals yet, but supposedly others have done that. It can NOT decode 
ATSC digital TV so don't even ask.

I do wish the SDR# software had some "save setup" features and a way to 
extract and display more data about the dongle and what it is doing. And 
I'd need a way to take a partially decoded data stream and pass it out 
to a second program to finish the decode.... There is still too much I 
don't know about the software and hardware, but what can you expect for 
30 minutes........

73, Doug Reed, N0NAS.