George Smart - M1GEO

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BA5SBA RTL-SDR Kit

Posted: 18 Jul 2017 03:51 PM PDT
https://www.george-smart.co.uk/2017/...a-rtl-sdr-kit/


A few weeks ago I ordered aÂ*BA5SBA RTL-SDR direct sampling kit from
BangGood (link here). When it arrived, I decided to put it together. The
kit includes everything needed, an RTL-SDR dongle, case, PCB, enamelled
wire and so on. I worked from numerous build instructions (here, here,
hereÂ*and here), following the clearest description of each stage.









I disassembled the original RTL-SDR dongle, removing the USB plug, IR
remote receiver and Belling-Lee socket. This was easy to do. I then
soldered the module into the main PCB. The SMT components were easy to
solder on. I added the few remaining passives, some larger electrolytic
capacitors, etc.

Two wires tack on to various voltage points to add extra smoothing, which
were easy enough to connect I used some medium thickness tinned copper
wire, I guess around 0.7mm diameter. That did the trick.

Winding the two inductors was done blindly. I followed instructions to wind
8 turns around a 5mm drill; however, somewhere else said 6-9 turns around
3mm. I noticed after soldering in the coils that 300nH was the suggested
inductance. In the future I will remake the coils to the correct value.

Winding the small transformer, T1, was relatively straight forward. I wound
8 turns around the ferrite core. Although Im not entirely sure my core was
ferrite. It was indistinguishable from a 2mm plastic washer. My kit had
blue-red-yellow trifiliar wire in, so I followed the colour scheme in the
3rd instruction link aboveÂ*(page 11).

The chip has two pairs of I-Q inputs, pins 1, 2, 4 and 5. The first pair,
pins 1 and 2 are connected to the E4000 front end, which mixes the higher
frequency signals of VHF and UHF down to an intermediate frequency (IF).
The second pair are also used in this kit to take the HF bands (on
theÂ*Realtek RTL2832U, 0-24 MHz) as a second IF input. A direct sampling
mode can be selected in the PC software to select this second input, but,
there is no default wiring as this has no use inside a TV tuner dongle.Â*By
far the hardest part of this build was the soldering of hair-sized wires to
the Realtek RTL2832U chip, which then go to the transformer, T1.



After a considerable struggle, these two wires were solder onto the chip. I
wish I could offer some useful tips on how I did this, but I cannot I
simply struggled, and faffed around until I made the connections. I would
suggest a mobile phone camera placed above the board may help, since you
can use the digital zoom to see in some detail. The image above was taken
as I was soldering.

Finally, I used some glue to hold the (very) fragile wires in position and
soldered the other ends to the transformer. I also added a small amount of
glue to the transformer, too, so as to stop it moving. It looks messy, I
know, but hopefully it will add some security and stability to those
otherwise poor solder connections to the Realtek chip.

My final build looked like this:

Amazingly it also works! The image at the top shows the device inside the
supplied box! Excellent!