By David, on June 18th, 2009%
The decibel was originally used by the telephone companies to quantify audio signal gains and losses in telephone circuits. The original unit was named the “bel” after Alexander Graham Bell, who was the inventor of the telephone.
In most electronics work, however, the bel is too large a unit, so we use the decibel, which is one-tenth of a bel. It’s referred to as “dB.”
In radio, the decibel is the expression of the ratio between two signals. The signals might be voltages, currents or power levels.
The formula to compute the decibel using the ratio of 2 power levels is:
dB = 10 LOG (P1/P2)
Where . . .
To read the rest of this article, please click here: → Decibels in Amateur Radio
By David, on May 19th, 2009%
You may have noticed that the popularity of balanced feed lines is on the rise.
There are a number of reasons why, and I may get in to that in another post. Right now I want to share with you a table that should make quite clear what the advantage of balanced feed line is.
A balanced feed line really outshines unbalanced (coaxial) feed lines when feeding a balanced antenna that is not resonant on the frequency of operation, such as in the case where a single doublet or dipole is being used as a multi-band antenna.
Take for example a 100 foot dipole elevated to 50 feet. This . . .
To read the rest of this article, please click here: → Why The Uprising in Balanced Feed Line Popularity
By David, on April 19th, 2009%
In Amateur Radio, you hear operators refer to their “rig.” A rig is basically any piece of equipment that can transmit RF for the for the use of the Amateur Service.
An Antenna is often called a “skyhook.” A station with several antennas has an “aluminum farm” or an “antenna farm.” In conversation the aluminum or antenna farm is often referred to as “the farm.”
A radio amateur who is going our to work on his antenna is going to “the farm.”
The term “set” as in a “radio set” and the term “aerial” which has been used to mean antenna, are both obsolete and are not used any . . .
To read the rest of this article, please click here: → Jargon
By David, on March 20th, 2009%
What is the difference between a voltage balun and a current balun?
This question just came up on the Hawaii Afternoon Net (which meets at 7.088 MHz, or 3.888 MHz when band conditions require it, at 0200 UTC (4PM HST) every day). The answer I gave was a quick one, but does answer the question.
A voltage balun is basically a transformer. You use it to transform the input impedance to some other value. 50 ohms to 300 ohms or 75 ohms to 600 ohm, or something like that.
A current balun is basically a choke. You would use it to present a very high impedance to an RF . . .
To read the rest of this article, please click here: → Voltage Balun vs. Current Balun
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