The graphs below show the computer predictions of filter performance forwarded to me by Harry PA0LQ. Click on the thumbnail sketch to show the full-size graph. One major problem in aligning the filter was that I did not (and still do not) have access to a frequency counter having a resolution better than 100 Hz. Given the choice, I would have foll
Click here to download the full size of the above Circuit.
owed Harry`s alignment instructions exactly. However, without the ability to make accurate frequency measurements, I had to devise an alternative method. This section describes my approach, using a dual beam [two channel] oscilloscope. Each of the four networks used resistor values as shown in Figure 2. Once the filter had been finally adjusted, a digital multimeter was used to measure the required value and hence select the required combination of fixed value components. Initially, I peaked all four stages of the filter to the frequency of the FT707 sidetone generator, at about 800 Hz. This resulted in a very narrow bandwidth - perhaps about 20 Hz. But this was far too narrow for practical purposes, because: Having decided to align the filter to the frequency of my sidetone generator, I used the oscilloscope`s Channel 1 input to monitor the input to the filter (from the FT707). The output of the filter was monitored using Channel 2, and also fed to a separate amplifier & loudspeaker. With all four stages of the filter still peaked to the frequency of the FT707 sidetone generator, the ringing could be seen quite clearly: when keying the FT707 with `dots` from my electronic keyer - the output of the filter never went to `zero`! Then, I set the electronic keyer to send dots at about 30 wpm rate. Using the remaining three variable resistors, I adjusted them with `skill and dexterity` [or was I guided by good fortune ] until...
This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of....
The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....
The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
The sub-harmonic bass generator is a sound producing unit for guitars. The sound it produces looks very much like that of the bass guitar. The octave generator is sometimes quite unusual since it does not produce any of the usual ways of coloring the sound,....
In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....
characters left: