Recent content by vk6kro

The fields around a conductor carrying radio frequency energy are the result of the current and voltage in the conductor. You can easily verify this. Just put a 1mm break in an antenna or a feed line and observe the effect on the antenna. The current is totally disrupted and so is the transfer...

The ladders in feed lines or antennas are almost always there to hold the wires at a fixed spacing. They are made of some suitable insulating material like ceramic or low loss plastic. The actual high frequency signal is an electrical AC voltage which has to travel in a metallic conductor...

Here is a useful website for calculating the time for an object to fall a known distance. http://keisan.casio.com/exec/system/1224835316 It just uses the standard formula, but it is a handy check. Your local observatory should be able to give you an accurate value for "g", the acceleration due...

The error with this experiment comes from using a steel ball bearing as the falling object. I used an electronic timer with 4 decimal place accuracy. The only variation in results was in the last figure and then only a slight variation. But the secret was to use the ball from an old computer...

Your electromagnet is probably too powerful. You could use a relay coil with the contacts removed. Place a computer mouse ball at the end of the relay coil and apply just enough voltage to attract the ball. You can drive this relay coil with a small power transistor. Just remove the power to...

A quick release can be made by reducing the voltage on the electromagnet so it is only just holding the falling object. For the falling object, do not use just a piece of iron. This will magnetise the iron and it will take a short while to let go. A better falling object is a ball from an old...

Consider just the primary winding on the transformer. It has an iron core and it has many turns of wire on it, so it has inductance. It has an applied AC voltage with a known frequency, so it has reactance. Reactance is the AC equivalent of resistance and it can be used in Ohms Law...

Power companies would love to charge for reactive current. Customers would object that they get no value from this so why should they pay for it? Imagine you were buying lobsters and the lobster dealer put them in a heavy wooden box before weighing them. Lobsters are expensive but wooden boxes...

You would have to measure the currents. Unless the motor comes with information about how much current it draws when supplied with 6 volts and with different loads, the only way you can find out is to measure it. You could put an ammeter in series with each motor, but this might cause the...

I like YouTube for this. If you go to www.YouTube.com in a browser. And type "radio fundamentals". There are dozens of videos there. Some are very well produced with gifted teachers, and you get it for free. Choose the topics that seem interesting but concentrate on ones that have thousands...

One problem with yagi antennas for TV is that they have to work over a wide bandwidth. So, an element that might work as a reflector at 77 MHz could start behaving like a director at 70 MHz. This would cause the frequency response to vary widely over the band required and it may cause the...

Yes, that would cover it. It would be easy with a simple FET amplifier with tuned step-up input and output circuits. Followed by an emitter follower, probably. But trying to make a RC amplifier with an opamp or a vacuum tube to do this seems to be asking for trouble. Note VK7.

Yes, but do you really want to go there? You would need a 6.3 volt heater supply, a 350 volt DC power supply, stringent safety precautions and some way of avoiding RF interference from the resulting device which would be a fairly potent transmitter. The opamp would have no way of producing 100...

A problem you may have is that, in an opamp, you will have gain, but it also affects the DC operating conditions of the opamp. So, you will find it very easy to get an output which is equal to one of the supply voltages. You then get, say, +12 volts output but no AC component at 1.2 MHz. You...

Since this is for a narrow bandwidth, you could ( and should) use tuned amplifiers. If you follow one amplifier with another, and both have a gain of 15, the combined gain will be about 15 times 15 or 225. I found an article I wrote a long time ago which may help...