the explanation for creating a computerized attenuator is the fact that a lot of times i have passed away by a reduced driven transmitter, because we forgot to make from the attenuation used regarding the more powerful sign. This attenuator utilizes the front end for the radio utilized to regulate the gain of this very very very very first phases. The radio that i personally use may be the Kenwood TR-751A. This can also be employed on other kind radios, but would need some noticeable modifications to your control voltages utilized. At the very least 3 cables want to result from radio stations. Ground, S-meter sign, additionally the gain control voltage returning to the air. I take advantage of more; for sale in radio stations are many voltages you can use with this specific setup. +13.6 switched, +8V, -8V. When you look at the attenuator that i will explain, We just make use of the +8V and I also create the -8V internally. I take advantage of twenty display that is led but any quantity of LedпїЅs may be used. Just adjust the circuitry accordingly. The Led display really does unique, it of program shows the general power regarding the sign, but inaddition it shows the general environment for the attenuator. The Led display makes use of the LM3914 Led motorist. Click image to see bigger variation go ahead and copy and printing This device is programmed to provide an illustration regarding the input in a fashion that is linear. We plan it in to the Dot mode although the sign energy generally seems to show in a club graph. Within the circuit the clock timer clamps the input at zero volts, then allows the sign fee a capacitor towards the complete voltage. This is accomplished at a tremendously higher rate, it is therefore hidden into the attention. This indicates as a string of lit ledпїЅs because of the final someone to be illuminated since the brightest. This really is helpful at evening to exhibit the size of the display. Additionally in the period the sign is clamped to zero (gnd), the voltage that is relative to your attenuation circuit is shown as being a single brightly lit led. The setting of this attenuation degree is https://mycashcentral.com/payday-loans-pa/ defined having a ten-turn pot, this may be a turn that is single, nevertheless the quality for the one change will be too abrupt.
The S-meter comes into cooking cooking cooking cooking pot 3; this might be utilized to cut the full-scale voltage associated with s-meter such that it corresponds to complete scale on the led meter.
This would go to a buffer amp, in order to perhaps maybe perhaps not load straight down the circuit that is s-meter the 751. The buffer has another input, that is used to set the zero sign degree in the very very first led. The production of the amp passes through a resistor that is 1k an analog gate 4066 pin 4. plus it would go to 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 make a clk sign. The attenuation control voltage is diverse because of the 10K 10-turn pot ( perhaps perhaps maybe not numbered). This sign undergoes an emitter follower 2N3906; this signal would go to 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 just a quad op-amp chip, one of several amps (pins 12,13,14) is employed as a clock for the 4027-control toggle, and also this clock runs at about 1HZ. The 2 other are employed as degree detectors. The lower one acts, because the point in which the attenuator will switch off, and also the top one determines at what degree the attenuator will start working. In between your attenuation shall stay since set. We set mine at about 15-20% and above 90per cent. The 4027 toggle will toggle into the continuing declare that both of these degree detectors dictate. Down when you look at the reduced corner that is right a capacitive degree converter that creates the negative voltages required for the appropriate procedure regarding the op-amps. (Note: you could go for a rail-to-rail op-amp and possibly not require the voltage that is negative 7662). The buffer amp may also drive an analog meter through the cooking cooking pot 5 and 3K, if you like. Additionally in the input a fast/slow switch slows the sign down a little whenever hefty modulation could potentially cause bouncing associated with the s-meter.
Okay, this is certainly for the 751A Auto Attenuation Mods. Click image to see bigger variation
You certainly will observe that lot significantly more than the four cables are coming to the 751A. The reason being I had this mod for any other attenuators so might there be additional cables shown. I utilize additional cables when it comes to ground sign, you do what you need. We additionally make use of a 10 conductor ribbon cable by having a fast disconnect, thus I can run the air without having the attenuator. Okay, in the left you will observe a tiny wire that is red this cable may be the +13.6 volts that is switched utilizing the on / off switch. It really is associated with the orange wire 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 when the s-meter sign visits the attenuator package. Brown, Ebony, green, and Violet is attached with ground. The gray cable is from the attenuator field, to regulate the leading end gain associated with the 751A. It attaches to your root of the 2N3904 transistor. Taking a look at the circuit, a ferrite bead can be used through the emitter follower into the stage that is pre-amp. I do believe the others is quite clear. Don KF6GQ click photo to see bigger variation Don KF6GQ