How do you know that fuse is protecting your circuit?

How do you know that this fuse will protect your rig?

How do you know that this fuse will protect your rig?

I blog for a leading manufacturer of circuit protection devices, so I keep my eye out for articles on fuses, ESD diodes and the like. Recently, I came across the article, “Fuse selection factors critical to circuit design.” Among the factors discussed is:

11. Application testing/verification prior to production.
Request samples for testing in the actual circuit to verify the selection. Before evaluating the samples, make sure the fuse is properly mounted with good electrical connections, using adequately sized wires or traces. The testing should include life tests under normal conditions and overload tests under fault conditions to ensure that the fuse will operate properly in the circuit.

Being a former test engineer, this got me to thinking about how one would actually do this. For example, how would you test that a fuse will actually protect a circuit board? Would you inject faults, i.e. deliberately short-circuit nodes? If so, which ones?

What measurements would you make to ensure that the fuse was working as you hope? Would you measure the time elapsed between the time you injected the fault until the time the fused actually blew? How about measuring the current profile over that period of time? That might be important and/or tell you something about the failure.

What kind of fault analysis should you perform after the fuse has blown? I suppose at the very least you’d want to replace the fuse and ensure that the circuit is functioning again. I would say that you should also run a full performance test to ensure that the fault didn’t adversely affect the board’s performance. Also, I’d think that you’d want to visually inspect the board to ensure that the fault current didn’t damage the board or traces at all.

I’m curious if any of you have had any experience with this kind of development testing. If so, please e-mail me or comment here.

From my Twitter feed: club resources

arrl's avatarARRL @arrl
ARRL Atlantic Division Adds Resources to Aid Amateur Radio Clubs: The ARRL Atlantic Division leadership has cr…

Atlantic Division director Bill Edgar, N3LLR, is truly one of the directors that knows what he’s doing.


qrparci's avatarQRP ARCI @qrparci
The Rockmite is back ! A HF transceiver with built in keyer for $40 –][.… #hamr #hamradio #qrp

The Rockmite is a classic. If you haven’t built any kits lately, consider picking up one of these and doing so.


AlanAtTek's avatar

Alan Wolke W2AEW @AlanAtTek
Lots of folks liked my “how to test BJTs” video, and asked for a similar one on MOSFETs. Here it is:…Another great W2AEW video. I don’t know how he has time to do these, but they’re certainly worth watching.

2014 Tech study guide: schematics and components (part 4)

My study guide covers the questions in T6C and T6D of the question pool in four separate sections. Overall, the question pool committee added several questions to T6C and T6D. In this section, T6D12 is an added question…Dan

There are many different types of components in modern radio equipment. Below, we will describe the types of components you will need to know about to pass the Technician Class license examination.

A relay is a switch controlled by an electromagnet. (T6D02)

Meters are devices used to indicate many different values. For example, a meter can be used to display signal strength on a numeric scale. (T6D04) Meters are also used to indicate the output voltage of a power supply, the output power of a transmitter, and many other parameters.

Integrated circuit is the name of a device that combines several semiconductors and other components into one package. (T6D09) Integrated circuits may perform either analog or digital functions. One type of analog integrated circuit that is very common is the voltage regulator. A regulator is the type of circuit that controls the amount of voltage from a power supply. (T6D05)

An LED is commonly used as a visual indicator. (T6D07) LED is short for light-emitting diode. They come in a variety of colors.

When connecting electronic assemblies together, we often use cables with one or more conductors. Some of those conductors may have a shield around them that is connected to ground. A common reason to use shielded wire is to prevent coupling of unwanted signals to or from the wire. (T6D12)

2014 Tech study guide: schematics and components (part 3)


My study guide covers the questions in T6C and T6D of the question pool in four separate sections. Overall, the question pool committee added several questions to T6C and T6D. In this section, T6D11 is an added question…Dan

The circuit shown in Figure T3 is the output circuit of a transmitter. Component 3 in figure T3 is a variable inductor. (T6C10)

There are two variable capacitors in this circuit—component 2 and the unlabeled component. A capacitor is used together with an inductor to make a tuned circuit. (T6D08)

Component 4 in figure T3 is an antenna. (T6C11)

An inductor and a capacitor connected in series or parallel to form a filter is a simple resonant or tuned circuit. (T6D11) When the capacitor and inductor are connected in series, the circuit has a very low impedance at the resonant frequency. When the capacitor and inductor are connected in parallel, the circuit has a very high impedance at the resonant frequency.

2014 Tech study guide: semiconductors

The Question Pool committee made several changes to the questions in this chapter. I like the changes. They make it easier to understand the idea of a transistor, I think…Dan

A diode is an electronic component that allows current to flow in only one direction. (T6B02) Diodes have only two electrodes. Anode and cathode are the names of the two electrodes of a diode. (T6B09) A semiconductor diode’s cathode lead is usually identified with a stripe. (T6B06)

Light-emitting diodes are a particular type of diode. When current flows through them, they emit visible light, making them useful as indicators and as part of digital readouts. The abbreviation “LED” stands for Light Emitting Diode. (T6B07)

Transistors are electronic components capable of using a voltage or current signal to control current flow. (T6B01) The transistor is a component that can be used as either an electronic switch or amplifier. (T6B03) Gain is the term that describes a transistor’s ability to amplify a signal. (T6B12) The transistor is an electronic component that can amplify signals. (T6B05)

A transistor is a component made of three layers of semiconductor material. (T6B04) Bipolar junction transistors have layers that are either P-type, which means that it has a positive net charge, or N-type, which means it has a net negative charge. Each layer has an electrode, making the transistor a device with three leads.

There are two types of bipolar junction transistors: PNP or NPN. A PNP transistor has two P layers, with an N layer sandwiched between them. An NPN transistor has two N layers, with a P layer sandwiched between them. The three electrodes of a PNP or NPN transistor are the emitter, base, and collector. (T6B10)

Another type of transistor often found in amateur radio equipment is the field-effect transistor. The abbreviation “FET” stands for Field Effect Transistor. (T6B08) FETs, like NPN and PNP transistors have three leads. Source, gate, and drain are the three electrodes of a field effect transistor. (T6B11)

2014 Tech study guide: resistors, capacitors and capacitance, inductors and inductance, batteries

Below is the “Electronics principles and components: resistors and resistance, capacitors and capacitance, inductors and inductance, batteries” section of the 2014 edition of the No-Nonsense Technician Class License Study Guide. As always, comments welcome…Dan

A resistor is the electrical component used to oppose the flow of current in a DC circuit. (T6A01) Most resistors have a fixed value, which is specified in ohms.

Some resistors are variable, that is you can change the resistance of the resistor by turning a shaft or sliding a control back and forth. These variable resistors are called potentiometers. A potentiometer is the type of component that is often used as an adjustable volume control. (T6A02) Resistance is the electrical parameter that is controlled by a potentiometer. (T6A03)

The type of electrical component that consists of two or more conductive surfaces separated by an insulator is a capacitor. (T6A05) A capacitor is the electrical component that stores energy in an electric field. (T6A04) Capacitance is the ability to store energy in an electric field. (T5C01) The farad is the basic unit of capacitance. (T5C02)

The type of electrical component that stores energy in a magnetic field is an inductor. (T6A06) The electrical component that is usually composed of a coil of wire is an inductor. (T6A07) The ability to store energy in a magnetic field is called inductance. (T5C03) The henry is the basic unit of inductance. (T5C04)

A switch is the electrical component used to connect or disconnect electrical circuits. (T6A08)

A fuse is the electrical component used to protect other circuit components from current overloads. (T6A09)

As amateur radio operators, we often use batteries to power our radio equipment. Some types of batteries are rechargeable, while others are not. The battery type that is not rechargeable is the carbon-zinc battery. (T6A11) All of these choices are correct when talking about battery types that are rechargeable (T6A10):

  • Nickel-metal hydride
  • Lithium-ion
  • Lead-acid gel-cell

You need a blivet

Brad, AA1IP, wrote to the Glowbugs group:

Disappointed and grumpy because ol’ Sanitary Claus didn’t being you any radio-related presents? Put on your 22, get on your toes and tapdance out an order for a Blivet or Blivette to restore your holiday cheer!

For $9.87, you receive a small USPS Priority flat-rate mail carton– a Blivette– stuffed with miscellaneous electronic parts: some are old, some are new, some are used and removed from equipment, and some are blew, er, blue.

For $23.23, you receive a medium USPS Priority flat-rate mail carton– a Blivet– stuffed with the same contents as above, only more so.

Note that the price of a Blivet or Blivette includes  postage to U.S. addresses only. Overseas postage charges are steep.

Questions welcomed, PayPal honored. Please make sure that your PayPal invoice includes your preferred USPS delivery address.

Now go build a radio!

I just sent off for a Blivette. I’ll let you know what I get.

From my Twitter feed: bypass caps, VHF propagation, SMD rework

dangerousproto's avatarDangerous Prototypes @dangerousproto
app note: properties and application of bypass capacitors

georgesmartuk's avatarGeorge Smart @georgesmartuk
Not sure if everyone has seen @ng0e‘s fantastic VHF Propagation Map from #APRS data. How genius! #hamr #hamradio #vhf

DIYEngineering's avatarDIY Engineering @DIYEngineering
app note: Rework method for surface mount MLCCs – Things you might need to know about doing SMT rework on Multi La…

Transforming impedances: Question G5C07

In the last two weeks, I’ve received e-mails from two readers of The No-Nonsense General-Class License Study Guide. Both questioned my explanation of how transformers transform impedance. I wrote:

Transformers are also used to transform impedances. The impedance ratio is also related to the turns ratio, but the transformation is equal to the square of the turns ratio. The turns ratio of a transformer used to match an audio amplifier having a 600-ohm output impedance to a speaker having a 4-ohm impedance is 12.2 to 1. (G5C07)

Doug wrote, “The only way I can reproduce the calculation is by taking the square root of the turns ratio.” His comment made me see where my explanation could be a bit misleading. I wrote back:

Think about it this way. An impedance transformation can go either way. When transforming from a higher impedance to a lower impedance, you divide by the square root of the turns ratio. When transforming a lower impedance to a higher impedance, you multiply by the square of the turns ratio. In either case, the impedance ratio is “related” to the square of the turns ratio.

I love getting feedback from my readers. Feedback like this helps me improve my study guides. If you have used one of my study guides, and have a comment or question about any of the material, please feel free to contact me.

From the trade magazines: litz wire, vector network analyzers, SDR

Another selection of amateur radio related items appearing recently in the electronic engineering trade publications.

Litz wire and other component cleverness
If you’re not familiar with it, litz wire is not named after a person or a place. It’s short for Litzendraht, the German term for braided, stranded, or woven wire. It’s a very clever solution to the problems and inefficiencies caused by the skin effect — as the frequency of the current that a wire carries increases, the current tends to go to the outside of the wire.

Vector network analyzers support versatile testing
Among the most valuable of RF/microwave test tools is the vector network analyzer (VNA), which can measure amplitude and phase with frequency. VNAs have long become associated with the measurements of complex impedance parameters—such as scattering (S) parameters—using the test data to design efficient impedance matching networks for the optimum transmission of high-frequency signals through active and passive devices and networks. At present, VNAs are available from both well-known and not-so-well-known instrument manufacturers, in both bench top and portable configurations for making measurements on high-frequency (HF) through millimeter-wave-frequency signals.

Integrated RF analog, multi-standard, software-defined radio receivers
The scaling of CMOS technologies typically has a great impact on analog design. The most severe consequence is the reduction of the voltage supply. Imec and Renesas have managed to put a complete, high-performance SDR (Software Defined Radio) receiver into a 28nm CMOS process with a 0.9V power supply. The IC has everything except a PLL on a single monolithic chip. (See Figure 1.) This is an impressive integration of analog functionality.