the explanation for creating a computerized attenuator is the fact that a lot of times i have passed away by a lesser driven transmitter, because we forgot to make the attenuation off getting used regarding the more powerful sign. This attenuator makes use of the end that is front of radio utilized to manage the gain for the very first phases. The radio that i take advantage of may be the Kenwood TR-751A. This may also be employed on other kind radios, but would need some noticeable modifications into the control voltages utilized. At the very least 3 cables have to result from radio stations. Ground, S-meter sign, therefore the gain control voltage returning to radio stations. I take advantage of more; for sale in radio stations are many voltages which can be used with this specific setup. +13.6 switched, +8V, -8V. Within the attenuator that i will explain, We just make use of the +8V and I also produce the -8V internally. I personally use twenty display that is led but any number of LedпїЅs can be utilized. Just adjust the circuitry accordingly. The Led display really does a number of things, it of program shows the general energy of this sign, but inaddition it shows the general environment regarding the attenuator. The Led display makes use of the LM3914 Led motorist. Select photo to see bigger variation Please feel free to copy and printing This device is programmed to provide a sign regarding the input in a linear fashion. We plan it to the Dot mode although the sign power generally seems to show in a club graph. Within the circuit the clock timer clamps the input at zero volts, then lets the sign fee a capacitor towards the complete voltage. This is accomplished at a rather rate that is high therefore it is hidden to your attention. This indicates as a string of lit ledпїЅs with all the final anyone to be illuminated once the brightest. This might be helpful at evening showing the size of the display. Additionally in the period the sign is clamped to zero (gnd), the voltage that is relative into the attenuation circuit is shown as being a single brightly lit led. The environment associated with the attenuation degree is defined having a ten-turn pot, this may be a turn that is single, nevertheless the quality associated with one change will be too abrupt.
The S-meter comes into cooking cooking cooking pot 3; this really is utilized to cut the full-scale voltage of this s-meter such that it corresponds to complete scale on the led meter.
This would go to a buffer amp, in order to maybe maybe maybe perhaps not load straight down the s-meter circuit in the 751. Another input is had by the buffer, that is used to set the zero sign level during the very very very very first led. The production of this amp passes through a 1k resistor to an analog gate 4066 pin 4. plus it visits the .5uf (.47uf) limit that is held to ground until TLC555 pin 7 allows it get (note: must make use of the CMOS variations associated with the 555 NOT the LM555). The production is /clk and also visits a 4066 inverter to make a clk sign. The attenuation control voltage is diverse because of the 10K 10-turn pot ( perhaps maybe maybe perhaps not numbered). This sign passes through an emitter follower 2N3906; this sign visits an analog gate 4066 pin 11. This gate turns from the attenuation voltage visiting the 751, when it’s not necessary. The TL084 is a quad op-amp chip, one of many amps (pins 12,13,14) is employed being a clock for the 4027-control toggle, and also this clock operates at about 1HZ. The 2 other are employed as degree detectors. The lower one acts, because the true point where in fact the attenuator will turn fully off, and also the top one determines at what degree the attenuator will start working. In between your attenuation will stay because set. We set mine at about 15-20% and above 90per cent. The 4027 toggle will toggle to your continuing declare that those two degree detectors dictate. Down when you look at the reduced right part is a capacitive degree converter that creates the negative voltages essential for the correct procedure of this op-amps. (Note: you could opt for a rail-to-rail op-amp and possibly not require the voltage that is negative 7662). The buffer amp can also drive an analog meter through the cooking cooking cooking cooking pot 5 and 3K, if you prefer. https://title-max.com/payday-loans-ms/
Okay, this is certainly for the 751A Auto Attenuation Mods. Select photo to see bigger variation
You will definitely remember that a complete lot a lot more than the four cables are coming to the 751A. Simply because I experienced this mod for any other attenuators so are there additional cables shown. I usually utilize additional cables for the ground sign, you do what you need. We additionally make use of 10 conductor ribbon cable by having a fast disconnect, and so I can run radio stations with no attenuator. Okay, in the left you will notice a tiny red cable, this cable could be the +13.6 volts that is switched aided by the on / off switch. Its related to the orange cable taken from J9. Ground is chosen through to the gnd pin of TP201. The +8V is selected up from pin 8 (yellow cable) of IC3, here is the S-meter amplifier. Pin 1 ( white cable) is where the s-meter sign would go to the attenuator field. Brown, Ebony, green, and Violet is attached with ground. The wire that is gray from the attenuator package, to regulate the leading end gain for the 751A. It attaches into the root of the 2N3904 transistor. Taking a look at the circuit, a ferrite bead is employed through the emitter follower to your stage that is pre-amp. I do believe the others is quite clear. Don KF6GQ click photo to see bigger variation Don KF6GQ