By David, on August 7th, 2011%
Just some notes I made on a napkin while researching this, and thought I should capture it somewhere.
FB-102 and FB-124 have 1/2″ holes which are the right size for RG-8 Coax.
Mix 77 is better for 80/160 meters Mix 64 is better for the higher frequencies (10 meters and up?) Mix 43 is a good all-around general purpose mix
12 of the FB-77-1024 on a suitable length of RG-8 will have enough RF impedance along the outside of the shield to function as a good balun. Type 73 is actually recommended, but seemingly hard to find. Type 77 will work very well.
You’re welcome to share any . . .
To read the rest of this article, please click here: → Miscellaneous Notes About Ferrite Beads and Baluns
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 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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