August 8, 2007
Tom Goyne, N4NSP
Earl Evans, KE4NBX

Abstract: Typically UHF frequencies perform poorly when trees, mountains and / or man-made objects form significant RF obstructions, making them less suitable for voice and digital emergency communications. This article discusses a UHF RF diffraction experiment that provided communications adequate for simulated Search and Recovery (SAR) operations by using a UHF repeater to transmit a strong, directed signal over an intervening mountain to a mountaintop ‘incident site.’     Read More ...

February 1, 2007
Dave Potter, W4RPI

Modulation Index for frequency modulated transmitters is given by

               

Where is the Modulation Index
D is the peak deviation (1/2 difference between maximum and minimum frequency)
m is the modulation frequency in hertz.

The interesting fact is that when the modulation index is 2.4, 5.52 or 8.65 the amplitude of the carrier vanishes.

Follow this link to learn how to use this fact help set the deviation of an FM transmitter. Read More ...

January 13, 2007
Henry Wyatt II, K4YCR
ARRL VA SEC

An excellent and relatively inexpensive “smart-charger”

Let’s take a hypothetical weather event, one that the “Weather Channel” says is going to be the worst in years. You are planning ahead though … batteries have been charged and you head-out for the EOC (or the nearby shelter) with that fully charged pack and a spare. Twenty minutes after you arrive, the first pack goes belly-up and after a few choice words, you substitute the spare pack.

Are you working on borrowed time? Can you work the rest of the eight-hour shift without a communications blackout? Knowing the condition of the batteries is an absolute necessity.

Do you have a way to check each cell in the pack to find the weakest link? I am not trying to sell a battery analyzer, but if you can borrow one, or maybe the local club can obtain one, it can be tried by everyone, probably to their amazement. It did me!

Follow this link for more details on how to make sure you batteries are up to snuff. Read More ...