the explanation for creating a computerized attenuator is a lot of times i have passed away by less driven transmitter, because we forgot to make the attenuation off getting used regarding the more powerful sign. This attenuator utilizes the end that is front of radio utilized to manage the gain associated with the very first phases. The radio that i take advantage of may be the Kenwood TR-751A. This might also be employed on other kind radios, but would need some noticeable modifications to your control voltages used. At the very least 3 cables need certainly to originate from radio stations. Ground, S-meter sign, together with gain control voltage returning to the air. I personally use more; obtainable in radio stations are a few voltages which can be used using this 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 produce the -8V internally. I take advantage of twenty Light-emitting Diode display, but any quantity of LedпїЅs can be utilized. Just adjust the circuitry properly. The Led display really does unique, it of program shows the general energy for the sign, but it addittionally shows the general environment for 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 in 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 cost a capacitor into the complete voltage. This is accomplished at a tremendously rate that is high it is therefore hidden into the attention. This shows as a string of lit ledпїЅs utilizing the final someone to be illuminated whilst the brightest. This really is helpful at to show the length of the display night. Additionally at that time the sign is clamped to zero (gnd), the general voltage going towards the attenuation circuit is shown being a single brightly lit led. The environment for the attenuation degree is defined with a ten-turn pot, this may be a solitary change cooking pot, nevertheless the quality associated with one change will be too abrupt.
The S-meter comes into cooking cooking pot 3; that is utilized to cut the full-scale voltage for 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 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 undergoes a 1k resistor to 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 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 ( maybe perhaps perhaps maybe not numbered). This sign experiences 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, if it is not necessary. 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 operates at about 1HZ. The 2 other are employed as degree detectors. The lower one acts, once the true point where in actuality the attenuator will switch off, while 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 the suggest that those two degree detectors dictate. Down within the reduced corner that is right a capacitive degree converter that creates the negative voltages essential for the correct procedure for the op-amps. (Note: you may 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 cooking cooking pot 5 and 3K, if you prefer. Additionally in the input a switch that is fast/slow the sign down a little whenever hefty modulation might cause bouncing associated with the s-meter.
Okay, this really is for the 751A Auto Attenuation Mods. Click photo to see bigger variation
You certainly will observe that a complete lot significantly more than the four cables are arriving to the 751A. The reason being I had this mod for any other attenuators payday loans CA so might there be additional cables shown. I usually use additional cables for the ground sign, you do what you would like. We additionally work with a 10 conductor ribbon cable with a disconnect that is quick therefore I can run radio stations with no attenuator. Okay, in the left you’ll see a little wire that is red this cable may be the +13.6 volts this is certainly switched utilizing the on / off switch. Its linked to the orange cable taken from J9. Ground is selected through to the gnd pin of TP201. The +8V is selected up from pin 8 wire that is(yellow of IC3, this is actually 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 field, to regulate the leading end gain associated with 751A. It attaches to your root of the 2N3904 transistor. Studying the circuit, a ferrite bead is employed through the emitter follower into the pre-amp phase. I do believe the others is fairly clear. Don KF6GQ click image to see bigger version Don KF6GQ