QUICK PROJECT: Improving the Freecom 25451 Rev3 DVB-T stick

I’ve finally gotten sick of the incredibly dire SMB connector on my Freecom 25451 Rev3 USB DVB-T receiver ‘stick’. The adapter that converts the SMB into a more standard Belling-Lee UHF connector (which is a horrible design as well, but a necessary evil around these parts) has been falling out, slipping and causing signal dropouts for weeks. All of this, of course, makes it rather difficult to watch any TV, let alone film4 (which is on Freeview Mux D — the mux on the Emley Moor transmitter that has the lowest transmission power).

At about this time, I decided the rat-bitten LNB cable on the Sky dish had to be replaced. This was duly done (earning me a great many cuts and scratches courtesy of the local flora) and I had a bag of half a dozen F connectors and a few metres of WF100 satellite cable left over. What better to do than fit a proper RF connector to the DVB stick?

The first step is getting the thing open. Hold the ‘451 with the “FREECOM DVB” logo badge facing upwards, the serial number label facing down, and the USB plug facing towards you. Insert a screwdriver in the gap between the top edge of the USB connector and the top section of the plastic case. Prise it apart gently until you hear a ‘snap’ as the first bit of glue gives way. Do this all the way around the ‘451, then pull it apart. Put the top cover to one side – you’ll need it later.

The next step is to remove the PCB. This is a bit easier – hold the base plastic, then lift the USB connector up and away. The SMB connector will snap out of the back when you do this.

Now desolder the SMB connector. Desolder the metal body of the connector using desoldering wick (you’ll need a lot of heat to do this — use a 50W solder station set to about 400 C). Once you’ve done that to all four pads (two on the top, two on the bottom), desolder the central pin. Remove the connector (careful, it’s hot!) and put it to one side. Clean up the solder pads by wiping the (clean!) tip of the soldering iron across them a few times.

Now prepare the cable. Cut a ~6in length of WF100 cable (the proper stuff is labelled “WEBRO WF100 CAI”). This is foam-core satellite-grade double-shielded low-loss coaxial cable, and is quite expensive, but the cost is worth it (and the foam is fairly heat-resistant). Strip about an inch of the outer insulation from both ends, without damaging the shielding braid. Pull the braid back, and separate it into four equally-sized bundles. Twist these bundles together to form four pigtails, then tin them. Remove the copper tape insulation and remove all but 5mm or so of the inner foam. The easiest way to do this is to cut half way through the foam all the way around the cable, then pull the two sections apart. Leave this section of the cable for now, and fit an F connector plug to the other end of the cable.

Put the now-bare end of the cable against the PCB, and cut the inner wire down so that it covers about three quarters of the PCB pad that was connected to the SMB connector’s inner pin. Match each of the four pigtails up with a ground pad and cut them down to match the ground pads. Solder the grounds down, then the centre wire.

Now check your soldering – make certain there are no little flakes of shielding touching the inner wire, and that the solder joints are solid and shiny. If they’re not, fix them. Also make sure you haven’t shorted out any of the pads – there’s not a lot of clearance, especially between the ground pads and the PCB components.

Put the PCB back into the case, and push it down. The co-ax cable will not sit properly in the grip that held the SMB connector – push it down firmly until it sits on the flat at the bottom. Fit the top cover and squeeze it together around the co-ax cable. You’ll note that one part of the top casing will not sit flush with the cable. Get a small file and trim it down a few millimetres so the case fits together correctly.

Now plug the USB stick in and test it. Make sure you can tune to a channel and watch TV as normal. If everything seems to work, take the bottom section (with PCB), put a few drops of superglue along the edge and squeeze the case together (I find the gel-type superglues easier to use for this). Hold it together until the glue takes hold. Leave it for about an hour (or so) to set.

There you go – one DVB-T stick with a “proper” RF connector. Fit a coupler to the F plug (of the sort used to connect two F plugs together), and make (or buy) a cable to go from your TV aerial outlet socket to the F connector on the coupler. Wire everything up, and enjoy.

Photos coming soon…