How to Choose a Replacement Transistor

Electus Distribution has published a short article on how to choose a substitute transistor. According to the article, you need to consider the application and the transistor’s basic characteristics, including:

  • whether it’s germanium (Ge) or silicon (Si);
  • NPN or PNP;
  • high power or low power;
  • designed for linear amplification or switching; and
  • low noise or not.

Also, note its main performance parameters, including:

  • voltage breakdown rating (usually Vcemax or BVceo);
  • current gain (beta or hFE) at the likely collector current; and
  • upper frequency limit (fT or Fmax).

UK EMC Journal Calls ‘Em Like They See ‘Em

G4TUT on QRZ.Com provided this pointer to the UK’s EMC Journal. In issue #83, they are running an editorial titled, “PLT, PLC, BPL: Call it what you like…it still interferes with the radio spectrum.”

That’s just the first salvo fired by this article. It goes on to say:

The EU (apparently supported by the UK Government) have treated with contempt legitimate complaints from some very respected organisations NATO, BBC, ERA Technology & York University plus many in Europe, these along with others being highlighted in other articles in this issue.

Why is this? It was recognised from the outset that PLT had inherent technical problems with respect to interference but such was the onslaught (lobbying) of the commercial interests that it was agreed Regulations would be overridden (ignored) in the interest of Broadband commercial success.

There are a couple of other very critical articles in this issue. Worth a read if you’re interested in or working on the BPL issue.

Practical Electromagnetic Shielding

The Clemson Vehicular Electronics Laboratory has a great little tutorial on electromagnetic shielding. The intro reads:

Shielded enclosures generally surround a product’s circuitry on all sides. Care is taken to ensure that all apertures are small and every seam is sealed. On the other hand, it is not uncommon to find shields that don’t surround the entire product. Often a shield partially covers only a few circuits. These shields may be penetrated by unfiltered wires and sometimes consist of a single plate of metal that may or may not be connected to ground.

Why are apertures and seams so important in some applications and completely irrelevant in others? The answer relates to the fact that there are different kinds of shielding for different applications. In the crosstalk notes, we saw that whether a cable shield needed to be grounded on one or both ends depended on the type of crosstalk we were trying to prevent. Similarly, circuit and system shielding requirements depend on the application.

It is convenient to divide shielding requirements into 3 categories: electric-field shielding, magnetic field shielding and shielded enclosures. Shielding strategies depend on the type of coupling we are trying to prevent.

Tin Whiskers 101

tinwhiskerTin whiskers can be real killers for electronics equipment, especially for electronics using no-lead solder. This primer on tin whiskers has all the basic information you need to know, including:

  • what they are,
  • what causes them, and
  • what you can do to avoid them.

Upcoming DXpedition to IOTA EU-051


Giorgio, IZ4AKS writes:

I often read your blog thanks to Google translator! I’d like to send you the news about my upcoming activity from Island of Ustica EU051.

Giorgio, IZ4AKS will be active as IE9X from the Island of Ustica IOTA EU-051 (IIA PA-001, MIA MI-116) from 16th to 21st of August 2009. Activity will be on 40-10 meters (manly SSB, but also RTTY and CW) with 100w and vertical antenna. QSL Policy: a special QSL in advance to all via BURO.

Best regards

73 de Giorgio IZ4AKS

How could I refuse a request like that? :)