The reason for creating 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 from the more powerful sign. This attenuator makes use of the front end of this radio utilized to regulate the gain associated with very very very first phases. The radio that i personally use may be the Kenwood TR-751A. This might also be employed on other kind radios, but would need some modifications to your control voltages utilized. At the very least 3 cables want to originate from the air. Ground, S-meter sign, together with gain control voltage returning to the air. I take advantage of more; obtainable in radio stations are a few voltages you can use with this particular 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 quantity 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 associated with the sign, but inaddition it shows the general environment associated with attenuator. The Led display makes use of the LM3914 Led motorist. Click photo to see bigger variation Take a moment to copy and printing This device is programmed to provide a sign of this 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 allows the sign fee a capacitor into the complete voltage. This is accomplished at a tremendously higher rate, so it’s hidden to your attention. This shows as a string of lit ledпїЅs because of the final anyone to be illuminated whilst the brightest. It is helpful at to show the length of the display night. Also during the time the sign is clamped to zero (gnd), the general voltage going towards the attenuation circuit is shown as being a single brightly lit led. The environment regarding the attenuation degree is defined by having a ten-turn pot, this may be a turn that is single, however the quality associated with the one change will be too abrupt.

The S-meter comes into cooking cooking cooking pot 3; it is utilized to cut the full-scale voltage regarding the s-meter such that it corresponds to complete scale on the led meter.

This would go to a buffer amp, to be able to maybe perhaps maybe not load along the circuit that is s-meter the 751. Another input is had by the buffer, that is used to set the zero sign degree during the very very very first led. The production of the amp experiences a resistor that is 1k an analog gate 4066 pin 4. plus it would go to the .5uf (.47uf) limit that is held to ground until TLC555 pin 7 allows it get (note: must utilize the CMOS variations for 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 by the 10K 10-turn pot ( perhaps maybe perhaps not numbered). This sign passes through an emitter follower 2N3906; this sign would go to 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, given that point in which the attenuator will turn fully off, additionally the top one determines at what degree the attenuator will activate. In involving the attenuation shall stay because set. We set mine at about 15-20% and above 90per cent. The 4027 toggle will toggle into the continuing suggest that those two degree detectors dictate. Down into the reduced corner that is right a capacitive degree converter that creates the negative voltages needed for the appropriate procedure associated with op-amps. (Note: you could opt for a rail-to-rail op-amp and possibly not want the negative voltage converter 7662). The buffer amp may also drive an analog meter through the cooking cooking pot 5 and 3K, if you need. Additionally on 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 might be for the 751A Auto Attenuation Mods. Click photo to see bigger variation

You may observe that lot significantly more than the four cables are arriving in 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, however you do what you need. We additionally make use of 10 conductor ribbon cable having a fast disconnect, thus I can run the air with no attenuator. Okay, in the left you will notice a little wire that is red this cable could be the +13.6 volts that is switched using the on / off switch. It’s associated with the orange wire taken from J9. Ground is selected through to the gnd pin of TP201. The +8V is selected up from pin 8 (yellow cable) of IC3, this is basically the S-meter amplifier. Pin 1 ( white cable) is where the s-meter sign would go to the attenuator field. online payday AZ Brown, Ebony, green, and Violet is mounted on ground. The wire that is gray from the attenuator package, to regulate the leading end gain for the 751A. It attaches to your foot of the 2N3904 transistor. Taking a look at the circuit, a ferrite bead is employed through the emitter follower into the stage that is pre-amp. I believe the remainder is quite clear. Don KF6GQ click photo to see bigger variation Don KF6GQ