the explanation for designing a computerized attenuator is the fact that a lot of times i have passed away by a diminished 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 regarding the very very very very first phases. The radio that i take advantage of may be the Kenwood TR-751A. This can be used on other kind radios, but would need some noticeable modifications to your control voltages utilized. At the very least 3 wires need certainly to originate from radio stations. Ground, S-meter sign, together with gain control voltage returning to radio stations. I take advantage of more; obtainable in the air are a few voltages you can use with this specific setup. +13.6 switched, +8V, -8V. Into the attenuator that i will explain, We just make use of the +8V and I also create the -8V internally. I personally use twenty Light-emitting Diode display, but any level of LedпїЅs can be utilized. Just adjust the circuitry properly. The Led display really does unique, it of program shows the strength that is relative of sign, but it addittionally shows the general environment associated with 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 fashion that is linear. We plan it to the Dot mode although the sign power generally seems to show in a club graph. Into the circuit the clock timer clamps the input at zero volts, then allows the sign fee a capacitor into the complete voltage. This is accomplished at a rather higher rate, so it’s hidden to your attention. This indicates as a string of lit ledпїЅs utilizing the final anyone to be illuminated once the brightest. This might be helpful at to show the length of the display night. Additionally at that time the signal is clamped to zero (gnd), the general voltage going towards the attenuation circuit is shown as being a single brightly lit led. The setting associated with the attenuation degree is placed by having a ten-turn pot, this may be a turn that is single, nevertheless the quality of this one change will be too abrupt.
The S-meter comes into cooking cooking pot 3; this will be utilized to cut the full-scale voltage associated with s-meter such that it corresponds to scale that is full the led meter.
This would go to a buffer amp, to be able to maybe maybe perhaps 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 degree during the very very first led. The production with this amp undergoes a resistor that is 1k an analog gate 4066 pin 4. plus it visits the .5uf (.47uf) limit this is certainly held to ground until TLC555 pin 7 allows it get (note: must make use of the CMOS variations associated with 555 NOT the LM555). The production is /clk and also would go to a 4066 inverter to create a clk sign. The attenuation control voltage is diverse because of the 10K 10-turn pot ( perhaps 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, if it is perhaps not required. The TL084 is a quad chip that is op-amp among the amps (pins 12,13,14) can be used being a clock for the 4027-control toggle, and also this clock operates at about 1HZ. The 2 other are utilized as degree detectors. The lower one acts, due to the fact point where in actuality the attenuator will turn fully off, as well as the top one determines at what degree the attenuator will start working. In involving the attenuation will stay because set. We set mine at about 15-20% and above 90per cent. The 4027 toggle will toggle to your continuing suggest that both of these degree detectors dictate. Down within the reduced right part is a capacitive degree converter that creates the negative voltages needed for the appropriate procedure of this op-amps. (Note: you could go for a rail-to-rail op-amp and perhaps not want https://cash-central.com/payday-loans-ms/ the voltage that is negative 7662). The buffer amp can also drive an analog meter through the cooking pot 5 and 3K, if you like. Additionally from the input a fast/slow switch slows the sign down a little whenever hefty modulation could potentially cause bouncing for the s-meter.
Okay, this might be for the 751A Auto Attenuation Mods. Click photo to see bigger variation
You can expect to keep in mind that lot significantly more than the four cables are arriving to the 751A. wet is because I had this mod for any other attenuators so are there additional cables shown. I utilize additional cables for the ground sign, however you do what you would like. I additionally work with a 10 conductor ribbon cable having a fast disconnect, therefore I can run radio stations without having the attenuator. Okay, in the left you will observe a little wire that is red this cable could be the +13.6 volts this is certainly switched with all the on / off switch. It really is associated with 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, this is actually the S-meter amplifier. Pin 1 ( white cable) is where the s-meter sign would go to the attenuator package. Brown, Ebony, green, and Violet is mounted on ground. The grey cable is from the attenuator package, to regulate leading end gain regarding the 751A. It attaches to your root of the 2N3904 transistor. Studying the circuit, a ferrite bead is employed through the emitter follower to your pre-amp phase. I do believe the others is fairly clear. Don KF6GQ click photo to see bigger variation Don KF6GQ