The 751 required turning the volume control almost to 12 o`clock before getting any hearable volume so I thought maybe something was wrong here. I replaced all the electrolytics associated with the audio path, i. e. after the detector stage and the audo amp. I couldn`t really hear any difference but at least I felt better. At this point, I dug out the scope and started
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looking at where the thumping was coming from. The 751 uses two electronic switches (IC7 C and D) to mute the audio, one for the actual audio and one for the monitor/sidetone circuit. The scope indicated that maybe these were causing the pulses generated when they were switched. (I should have realized at this point that this wasn`t the case because when switching to transmit a large positive pulse occured and when switching back to recieve a large negative pulse was generated. I figured out later what was happening. ) Anyway, I started cutting traces and adding jumpers and effectively bypassed the electronic switches. What I ended up doing was connecting the monitor and audio stages to the audio amp with no switching. This basically fixed the problem but I lost the use of squelch and the volume was reduced quite a bit. So I started looking elsewhere. A couple of things I learned was that the electronic switches were not needed for cw operation. The receiver mutes very well without them and the monitor/sidetone only works when the key is down. This is exactly what was needed. The electronic switches are really only needed for squelch operation but the circuit designers built the 751 so that the audio path is switched off when going to transmit and the monitor/sidetone audio path is switched on when in transmit. The 761 uses a couple of transistors to "short" the audio path to ground when in transmit. I built up a little...
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.....
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