Balun de aire relacion 1:1

Balun al aire relación 1:1

BALUN AL AIRE

Construcción de un balun al aire para un rango de frecuencias entre 3,5 y 30 Mhz.

El balun se un accesorio destinado a acoplarun sistema radiante simétrico, como es un dipolo, con un sistema asimétrico como es el cable coaxial. Este balun está construido en relación 1:1.

Sobre un núcleo en tubo de PVC de 25 mm de diámetro se construye una bobina trifilar de 12 espiras con hilo de cobre esmaltado de 2 mm de diámetro en la forma y modo en que se presenta en el dibujo.

Es importante observar, en la foto del balun, las conexiones de cada bobina y para mayor claridad he preferido dar a cada bobina un color diferente.

En el esquema se aprecian las conexiones y puentes de cada una de las bobinas.

TRASMISOR 1 W VALVULAR

MINIMALIST por LY3LP

RF Linear Hybrid Amplifiers

RF Linear Hybrid Amplifiers

Posted Jul 28th 2011

A new class of low cost, high performance hybrid amplifiers has emerged to assist the design engineer working in the frequency range of 1 to 500 MHz. Utilizing the low distortion and wide dynamic range performance technology developed for the CATV industry, these amplifiers feature power output capabilities previously unavailable in hybrid circuits.

RF linear hybrid amplifiers represent a new family of medium power, broadband gain blocks for multi purpose RF applications. Internally matched at both the input and the output for either 50 ohm or 75 ohm systems, these devices cover gains ranging from 17 to 35 dB, and can accommodate output power levels in excess of 400 mW. Linear class A bias conditions accommodate third order intercept values in excess of + 45 dBmV. Depending on quantity and model selected, most prices fall in the range of $30. to $60. If you’ve been using transistors like the 2N3866, 2N5109, or stud mounted devices, read on. You may save a lot more than just design time.

RF linear hybrid amplifiers utilize the thin film manufacturing and construction techniques developed for the demanding CATV industry. All ceramic substrates are alumina (A1203) with gold conducting paths. Resistors are either cermet or nichrome, and are laser trimmed to better than one percent tolerance. For maximum MTBF, gold metallized transistor die are used incorporating resistive ballasting in the emitter fingers to provide even thermal distribution across the surface corporating resistive ballasting in the emitter fingers to provide even thermal distribution across the surface of the die and to eliminate “hot spotting.” These transistor die are subjected to rigorous testing through an extensive wafer qualification program before being mounted on the circuit. The hybrid manufacturer must insure that the transistors used will meet the exacting requirements for gain, distortion, and noise figure.

CASCODE CLASE E

CLASS G AND CLASS H

Class G and Class H are quests for improved efficiency over the classic Class-AB amplifier. Both work on the power supply section. The idea is simple. For high-output power, a high-voltage power supply is needed. For low-power, this high voltage implies higher losses in the output stage.

What about reducing the supply voltage when the required output power is low enough? This scheme is clever, especially for audio applications. Most of the time, music requires only a couple of watts even if far more power is needed during the fortissimo. I agree this may not be the case for some teenagers’ music, but this is the concept.

Class G achieves this improvement by using more than one stable power rail, usually two. Figure 4shows you the concept.

Figure 4—A Class-G amplifier uses two pairs of power supply rails. b—One supply rail is used when the output signal has a low power (blue). The other supply rail enters into action for high powers (red). Distortion could appear at the crossover.

Mechanically-tuned portable DSP radios: a shootout

Posted on February 1, 2014 by Thomas

Three of the five contenders: The Degen DE32, Degen DE321 and Tecsun R-2010D (Click to enlarge)

Following is my premiere shortwave radio column for the January 2014 issue of The Spectrum Monitor digital magazine.  It takes the form of a review–or “shoot-out,” if you will–of a few select mechanically-tuned DSP radios I’ve tested over the years.

While I’m a big fan of print publications, digital publications like TSM offer me flexibility that I can’t get in traditional print: namely, shorter time to publication (thus more up-to-date information) and especially, the ability to embed links and audioas I do here on The SWLing Post. In this case, I’m able to include audio clips which the reader can utilize to compare the radios firsthand (embedded here, as well).

Note: This being my first contribution to a brand new magazine, I thought it would be fitting to begin by explaining why I still believe in shortwave radio…I mean, how could I resist? I guess I’ll always be a shortwave evangelist at heart.