From my Twitter feed: bipolar transistors, homebrew Buddipole, Dayton survival

Planet Analog ?@PlanetAnalog 11m
Bipolar Transistor Circuit Design & Analysis, Part 1 – There are many applications for one or two transistors. Th… http://ow.ly/2EzTJR 

 

n1pce's avatarJohn Ryan @n1pce
Homebrew Buddipole with Modifications: youtu.be/Z6ATX2Z9ews via @YouTube

You don’t have to pay a lot for a Buddipole. By making one yourself, you can not only save money, but learn something in the process.

ke9v's avatarJeff Davis @ke9v
Dayton Survival Guide ke9v.net/articles/dayto…

The Dayton Hamvention, still the largest gathering of amateur radio enthusiasts in the world, takes place May 16-18, 2014. While I disagree with Jeff’s statement, “There’s simply no way to facilitate that size of a crowd for three days in an ultra modern facility,” the rest is pretty much spot on.

From my Twitter feed: Santa, kits, PCB design

HamHijinks's avatarHam Hijinks @HamHijinks
Trying a new mode tonight: Santa Scatter! #hamr #hamradio

 

RigolTechUSA's avatar

Chris Armstrong @RigolTechUSA
The Rise, Fall, and Rise of Electronics Kits | @IEEESpectrum #IEEE goo.gl/wzTuv1

ke9v's avatar
Jeff Davis @ke9v
Design it. Order it. Build it. Very cool. fplus.me/p/4wc8

From the trade magazines: satellite tracking, online circuit design, open-source test board

More cool stuff from the electronics engineering trade magazines….Dan

LEO satellite tracking in your backyard. Learn how one guy built his own satellite tracking system in his backyard.

The rise of the online circuit-design collective. Though still in the infancy stage, design and simulation tools that run entirely in the browser are pushing their way onto the EDA landscape. The ultimate goal is that they become essential players within the realm of professional design.

Test and measurement  turns to open source, Kickstarter. The field of test and measurement is set to benefit from open-source software applications if a Kickstarter fundraising project is successful. The Red Pitaya is a credit card-sized, reconfigurable measurement board with 60MHz of input bandwidth and an onboard Xilinx Zinq FPGA to perform signal processing.

Are you isolated?

There are many times in amateur radio where you want to “isolate” two pieces of equipment or avoid “ground loops.” For example, when connecting a computer to a rig to do digital modes, you should isolate the signals so that there’s no direct connection between the rig and the radio.

What does it really mean to be isolated, though? And, for that matter, what is “ground”?

You can learn what these  terms actually mean and when and why you need isolation if you view the webinar Fundamentals of Signal and Power Isolation. Here’s how they describe the webinar:

This Fundamentals course will briefly look at power isolation (often required in conjunction with signal isolation) and then focus on signal isolation techniques. It will look why it is needed, where it is needed, the relative attributes of techniques for implementing it, and other considerations.

From the trade magazines: spectrum sharing, active filters, real capacitors

Passive components aren’t really so passive (Part 1): Capacitors. Transistors and ICs are considered active components because they change signals using energy from the power supply. Capacitors, resistors, inductors, connectors, and even the printed-circuit board (PCB) are called passive because they don’t seem to consume power. But these apparently passive components can, and do, change the signal in unexpected ways because they all contain parasitic portions. So, many supposedly passive components, like the capacitor shown below, aren’t so passive.

The model above shows that a capacitor adds more than just capacitance when you use it in a circuit.

Peaceful coexistence on the radio spectrum. How two engineers (shown at right) tried to get the military to share some spectrum with their small company.

Signal-chain basics #43: Active filters. While low-frequency filters can be designed with inductors and capacitors, they often require physically large and often expensive inductors. This is where active filters, which combine an operational amplifier (op amp) with some resistors and capacitors, become attractive. Active filters can provide an LCR-like performance at low frequencies

From my Twitter feed: future of SDR, Dayton review, fritzing

K9ZW
The Future of SDR – Fat-Pipe vs. Thin-Pipehttp://t.co/u6WpGGv6ML

 

ke9v
Dayton in the Rearview Mirror | Smoke Curlshttp://t.co/PI25XUisGR #hamr

 

g6avk
This looks like an interesting and easy to use PCB package - http://t.co/xsL7rY2t7n

From my inbox: 1, 2, 3-tube radios, cheap cap tester, cheap frequency synthesizer

  • Build a radio with three tubes or less. This article lists radios that you can build with three tubes or fewer. In general, this is a very cool website. (Thanks to Brad, AA1IP, and the Glowbugs mailing list.)
  • Cheap capacitance tester. The Glowbugs mailing list also recently had a discussion of cheap capacitance testers. I just bought a fancy, new Keithley DMM  that measures capacitance, but some of the instruments mentioned in this thread also measure inductance. The consensus seems to be that while they’re not as accurate as a “real” test instrument, for $20 or so, how can you go wrong?Brad, AA1IP mentions the article, “A Low Cost Automatic Impedance Bridge” by Dr. George Steber, WB9LIV, that appeared in the October 2005 QST. Brad says, “This arrangement uses a PC’s sound ports, a dual-section op amp, a few components and some software to deliver reasonably precise RLC measurements along with a graphic screen display.”
These frequency-synthesizer boards use the AD9850, and can be purchased on eBay for as little as $5 each.

These frequency-synthesizer boards use the AD9850, and can be purchased on eBay for as little as $5 each.

 

  • Cheap AD9850 boards. The AMRAD mailing list has a thread on these inexpensive signal-generator modules. One of the AMRAD guys has been experimenting with using them with an Arduino to make frequency control easier. They’re only $5 each and generate 0 – 40 MHz.On the Glowbugs list, they talked a little bit about these boards, too. One guy gave a link to the article, “An Improved VFO Driver Amp for Tube Rigs.” This article describes a circuit that allows you to easily use the AD9850 boards (or any other digital synthesizer, for that matter) as the VFO for a tube rig.

From my Twitter feed: Lids, EDA, TV

PD3EM
@KL8DX Publish your LID list onhttp://t.co/8hLu0GOy #LOTA #LidsOnTheAir

 

KD4E_73
http://t.co/Rq3ZqVgr links to Electronic Design Automation (EDA) tools that are released under the GPL.

Radio_2_Radio
Amateur Radio: Ham Radio in upcoming episode of Last Man Standinghttp://t.co/ME9vPCth

Extra Class question of the day: Amplifiers

There are several classifications of amplifiers, based on their mode of operation. In a class A amplifier is always conducting current. That means that the bias of a Class A common emitter amplifier would normally be set approximately half-way between saturation and cutoff on the load line. (E7B04)

In a class B amplifer, there are normally two transistors operating in a “push-pull” configuration. One transistor turns on during the positive half of a cycle, while the other turns on during the negative half. Push-pull amplifiers reduce or eliminate even-order harmonics. (E7B06)

A Class AB amplifier operates over more than 180 degrees but less than 360 degrees of a signal cycle. (E7B01) Class B and Class AB amplifiers are more efficient than Class A amplifiers.

A Class D amplifier is a type of amplifier that uses switching technology to achieve high efficiency. (E7B02) The output of a class D amplifier circuit includes a low-pass filter to remove switching signal components. (E7B03)

Amplifiers are used in many different applications, but one application that is especially important, at least as far as signal quality goes, is RF power amplification. RF power amplifiers may emit harmonics or spurious signals, that may cause harmful interference.

One thing that can be done to prevent unwanted oscillations in an RF power amplifier is to install parasitic suppressors and/or neutralize the stage. (E7B05) An RF power amplifier be neutralized by feeding a 180-degree out-of-phase portion of the output back to the input. (E7B08) Another thing one can do to reduce unwanted emissions is to use a push-pull amplifier. Signal distortion and excessive bandwidth is a likely result when a Class C amplifier is used to amplify a single-sideband phone signal. (E7B07)

While most modern transceivers use transistors in their final amplifiers, and the output impedance is 50 ohms over a wide frequency range. A field effect transistor is generally best suited for UHF or microwave power amplifier applications. (E7B21)

Many high-power amplifiers, however, still use vacuum tubes. These amplifiers require that the operator tune the output circuit. The tuning capacitor is adjusted for minimum plate current, while the loading capacitor is adjusted for maximum permissible plate current is how the loading and tuning capacitors are to be adjusted when tuning a vacuum tube RF power amplifier that employs a pi-network output circuit. (E7B09)

Figure E7-1

The type of circuit shown in Figure E7-1 is a common emitter amplifier. (E7B12) In Figure E7-1, the purpose of R1 and R2 is to provide fixed bias. (E7B10) In Figure E7-1, what is the purpose of R3  is to provide self bias. (E7B11)

Figure E7-2

In Figure E7-2, the purpose of R is to provide emitter load. (E7B13) In Figure E7-2, the purpose of C2 is to provide output coupling. (E7B14)

Thermal runaway is one problem that can occur if a transistor amplifier is not designed correctly. What happens is that when the ambient temperature increases, the leakage current of the transistor increases, causing an increase in the collector-to-emitter current. This increases the power dissipation, further increasing the junction temperature, which increases yet again the leakage current. One way to prevent thermal runaway in a bipolar transistor amplifier is to use a resistor in series with the emitter. (E7B15)

RF power amplifers often generate unwanted signals via a process called intermodulation. Strong signals external to the transmitter combine with the signal being generated, causing sometimes unexpected and unwanted emissions. The effect of intermodulation products in a linear power amplifier is the transmission of spurious signals. E7B16() Third-order intermodulation distortion products are of particular concern in linear power amplifiers because they are relatively close in frequency to the desired signal. (E7B17)

Finally, there are several questions on special-application amplifiers. A klystron is a VHF, UHF, or microwave vacuum tube that uses velocity modulation. (E7B19) A parametric amplifier is a low-noise VHF or UHF amplifier relying on varying reactance for amplification. (E7B20)

Extra Class question of the day: Modulation and demodulation

Modulation is the process of adding some kind of information, including voice and digital information, to a carrier signal. The most common types of modulation that we use in amateur radio are amplitude modulation (AM) and frequency modulation (FM). Single-sideband, or SSB, is a form of amplitude modulation.

To frequency modulate a carrier, a transmitter will sometimes us a modulator that varies the phase of the signal. This is sometimes called phase modulation (PM). One way to generate FM phone emissions is to use a reactance modulator on the oscillator. (E7E01) The function of a reactance modulator is to produce PM signals by using an electrically variable inductance or capacitance. (E7E02) An analog phase modulator functions by varying the tuning of an amplifier tank circuit to produce PM signals. (E7E03)

To boost the higher audio frequencies, a pre-emphasis network is often added to an FM transmitter. (E7E05) For compatibility with transmitters using phase modulation, de-emphasis is commonly used in FM communications receivers. (E7E06)

Amplitude modulation and single-sideband signals are produced using mixer circuits. The carrier frequency and the baseband signals are input to the mixer circuit which produces an amplitude modulated output. The term baseband in radio communications refers to the frequency components present in the modulating signal. (E7E07) The principal frequencies that appear at the output of a mixer circuit are the two input frequencies along with their sum and difference frequencies. (E7E08)

When using a mixer, you must take care not to use too high of a signal at the inputs. Spurious mixer products are generated when an excessive amount of signal energy reaches a mixer circuit. (E7E09)

Single sideband is most often used for phone transmission on the HF bands and for weak-signal operation on the VHF and UHF bands. One way a single-sideband phone signal can be generated is by using a balanced modulator followed by a filter.  (E7E04) A balanced modulator is a type of mixer.  The output of a balanced modulator, however, does not contain the carrier frequency, only the two sidebands.

Modern transceivers use digital signal processing to generate SSB signals. The quadrature method describes a common means of generating an SSB signal when using digital signal processing. (E7E13)

At the receiving station, a modulated signal has to be demodulated. Amplitude modulated signals are often demodulated using a diode detector circuit. A diode detector functions by rectification and filtering of RF signals. (E7E10)

For demodulating SSB signals, you want something a little more sophisticated. A product detector is a type of detector that is well suited for demodulating SSB signals. (E7E11) A product detector is actually a frequency mixer. It takes the product of the modulated signal and a local oscillator, hence the name. In an FM receiver, the circuit for detecting FM signals is a frequency discriminator. (E7E12)

Some modern receivers demodulate a signal entirely in software. These receivers are called software-defined receivers. When referring to a software defined receiver, direct conversion means incoming RF is mixed to “baseband” for analog-to-digital conversion and subsequent processing. (E7E14)