Saturday, 5 March 2016

Metal Cases

RTL-SDR dongles are extremely sensitive devices, capable of receiving a radio transmission from the other side of the world. This performance comes at a cost: local signals, such as commercial FM radio stations, pagers, or data control channels for trunked government communications will interfere with reception capabilities.
Since the beginning of radio, metal shielding (effectively a Faraday cage) has been used to keep unwanted signals away. The first performance-enhancing modification I recommend in the upcoming book is a metal case - homemade solutions will be cheaper and work just as well (physics is the same).
Tin cans, however, might not elicit a nodding embrace from your significant other, and wrapping in alu foil is not only unsightly, it prevents ventilation and therefore degrades ultimate performance due to higher internal temperature.
It's better than stock, but a metal case is the best.

Available Metal Cases under review:

- Metal Case and Thermal Pad Upgrade, $4.95 plus shipping (called "Silver case" here),
- Nooelec Extruded Aluminum Enclosure, $9.95 plus shipping ("Blue case"),
- Nooelec Extruded Aluminum Enclosure for Ham-It-Up, $21.95 plus shipping.

All units were received from the manufacturers for review, free of charge, no strings attached.
Wording: "aluminum" is American English, "Aluminium" is rest of the world. Same material. "Case" and "Enclosure" used interchangeably.
From "By the way, just a little correction for your post. Our metal case upgrade is $4.95 including shipping, not plus. Though, people who want it asap can still upgrade to express DHL/UPS etc shipping".

Which metal case to choose?

Depends on antenna connection.
Side-facing MCX antenna socket: majority of dongles on the market due to architecture used on cheap Chinese RTL-SDR dongles. Choose Nooelec's Blue Case.
Inline MCX / SMA socket: antenna connector plugs in on the other side of the USB port. dongle, Nano and E4000-based dongles from Nooelec. Choose's Silver Case.
PAL connectors e.g. Nooelec's Nano-P or similar half-size dongles with inline PAL connector just about fit the Silver Case.
Replacing a side-facing antenna connector with coax and using the cheaper Silver Case is an option, but requires soldering.

Nooelec Metal Case

Available in Blue and Silver, this will be compatible with the majority of RTL dongles on the market - if it's full size, with small MCX connector on the side, this will fit.
The first surprise is the weight of the plastic bag, containing the enclosure in two halves, two end plates and 8 screws. No instructions or screwdriver, but when you reached this stage of human evolution, you probably have one anyway.
It's built like a tank, wall thickness is reassuring, does not bend or flex. Images do not do justice nor convey the robustness of this thing; it's a relic from a bygone era, when metal was thick metal.
Screws are countersunk, large enough for a common Philips screwdriver. Fully assembled, the RTL stick setup is heavy enough to inflict major damage on home invaders should you run out of double-ought shot.

Four flat sides without heat dissipation fins: this is good for those who'll create a hedgehog with heatsinks, and bad for the average user as fins are generally preferred. Development idea: provide cooling fins on two sides to keep everyone happy.

Interior volume is sufficient to please the "stick a heatsink onto the chipsets" crowd, enough clearance for common RasPi heatsinks.

The case is so wide and tall that nearby USB ports will be unusable: forget other ports on the RasPi without an extension cable. For a headless PiAware / remote access via Ethernet only setup it's not a concern, but you may struggle in other scenarios. Metal Case and Thermal Pad Upgrade's own dongle already wears this metal enclosure, but retrofitting is possible for older versions and it's the right choice for half-size Nano or E4000 sticks from Nooelec: sadly, there's no official case available for them.

The silver case is a half-price alternative, with half the material, thinner screws, but narrower USB-port friendly profile and equal performance.

Adding heatsinks will be complicated, rounded top and bottom provide less contact area.

E4000 users: order the case from, will be a loose fit at the antenna connector, but hole on the other side is large enough for standard RG-59 or RG-6 coax to pass through - use the connector on the coax that came with the dongle as a the antenna connector. Cover chipsets with thermal pad for better heat transfer.

Both metal cases work extremely well, adding a thermal pad to the silver case was a wise move, the customer gets more.

Ham-It-Up v1.3 aluminum enclosure

Specifically made for this upconverter, same material as dongle case. Old v1.2 users note that the new enclosure will NOT be compatible, order side panels for $9.99 if you upgrade.
Massive and creates a hefty package, deliver final blows to said home intruder and case will come out of the confrontation unscathed. Intruder won't. Two additonal PC-screws line up with holes on the bottom for additional mounting options. All in all, a nice and well-thought out package, just like the dongle case - flush-mounted screws testify attention to detail.

Manufacturer claims "laser-etched labeling" just as with the dongle case - this is laser engraving to you and me, and works since the markings will not come off.
After placing the PCB in the case, it will be still somewhat loose and prone to rattling when shaken, this goes away as soon as connectors are connected.

Cooling fins on the side help with heat dissipation, completely flat bottom, and sizable top surface allows fixing huge heatsinks on securely.

Update March 7: Toughness and alternatives

Toughness: tested all three cases featured here by driving a mid-size family sedan over all three.

No bother.

Alternatives: On reddit, contributors had a few suggestions for cheaper metal enclosures.

Should you buy a metal case?

Absolutely. Placing a radio device into a metal case will cut down on radio interference, provide physical security (the LEDs on the Ham-It-Up definitely need it) and help with cooling. And it looks cool.
Aluminum foil? A cheap and common solution is to wrap the plastic case of the dongle in alu foil. Will have the same effect as a metal case as long as the foil touches the metal connector (read the noise reduction post for further tips, or sign up for the book for even more tips and tricks. Alu foil is just the tip of the iceberg.)
Using alu foil is OK as long as you're aware of its limitations: reduced ultimate performance due to higher chipset temperature and no physical protection.
Buying a metal case is an additional expense, so most readers will probably dismiss the idea and be happy with DIY modifications. Don't. Professional radio gear always has a metal enclosure for a good reason - but if you're using your dongle now and then, spending $5 or $10 is unwarranted.
However, if an electronic device is in constant use, you rely on it for dependable performance, or you spent a considerable sum e.g. for a Ham-It-Up or an E4000 tuner, then bite the bullet and get a metal case.

If you enjoyed this article please pre-order my RTL-SDR
Guide Book on Amazon Kindle. More than a hundred pages of knowledge, information and diagrams for all levels of expertise.

Kindle is available for computers (Windows and Mac), and for smartphones and tablets (Android and Iphone, iPad and iPod touch).

If you're interested in the Raspberry Pi, please sign up for the upcoming book, which details the ins and outs of setting up, using and enjoying the Pi 3 microcomputer.

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