Blog Posted:7/1/2011 3:04:00 AM
Being a sometimes Ham radio operator, vk4pr.
I’m interested in this subject
Yes radio waves, tv waves, are all in the air around you, all you need is something to grab em.
A tuned circuit, a crystal set does it ....hook its antenna connection to a long wire and the radio waves come into it. The wave you want is grabbed by the tuner part of the crystal set .
A trap is used to get it?
In your battery radio you will see the tuning capacitor which moves as you change channel.
Alongside it you wil see a ferrite rod maybe with lots of wire wound on it.
So what you have is a movable condenser/capacitor in parallel with it sort of grabs the radio wave
at variable frequencys.
At the frequency you have selected or found by moving the condenser part ..Then the radio wave at am radio might be 512,000 times a second, how often it cycles per second, frequency vibration .
(we vibrate 6 times a second I’m told…10 times might be fatal, they tested that idea too, after an elevator buzz was making people sick in a building)
They say hertz per second but it used to be cycles per second 50 years ago.
So the aerial brings the frequency into the radio tuned trap of the coil and capacitor at 512kilocycles per second. Then it loses half or its cycle passing through a diode one way valve ( a one way only gadget) to get the voice audible . Now it goes to your crystal headphones so you hear the voice, or it goes to an amplifier and your woofers.
11 metre Cb radio 27 million cycles per second , used a quarter wave antennae about 9 foot long on your car. Good for taking out fluros at drive through bottle shops
But 2 metre ham radio at 146 million cycles uses about a 19 inch long quarter wave antennae. Frequency faster ariel gets shorter. It all works if you use maths . The mobile phone /radio uses a tiny antennae on it 2way radio and transmits a few milliwatts of tickle in your ear to the tower and your friend.
468 divided by 27 = 17.3333333333333333 etc feet so split it in the middle it will resonate around
27 megarhertz our cb frequency , half wave ant. Shorten or make longer to change the frequency per second. on your car you use half 8.6666666 feet the car body becomes the other half of a tuned circuit, a quarter wave vertical antennae.
So shorten length of vertical antennae to go back towards 28 megacycles.....faster cycle per second Shorter antennae...
The Ark of the Covenant might have been a radio it seemed to be a big capacitor and had dangerous voltages on it that killed men if handled wrongly. The old time valve radios also have dangerous voltages like the valve final amplifiers on Kenwood 520 Ham radios of the past.
By Don Johnson