the explanation for creating a computerized attenuator is a lot of times i have passed away by a lowered driven transmitter, because we forgot to make the attenuation off used regarding the more powerful sign. This attenuator makes use of the end that is front of radio utilized to regulate the gain associated with very very very first phases. The radio that i take advantage of may be the Kenwood TR-751A. This may be utilized on other kind radios, but would need some modifications into the control voltages utilized. At the very least 3 cables want to result from the air. Ground, S-meter sign, plus the gain control voltage returning to radio stations. I take advantage of more; for sale in radio stations are a few voltages you can use using this setup. +13.6 switched, +8V, -8V. When you look at the attenuator that i will explain, We only make use of the +8V and I also produce the -8V internally. I take advantage of twenty Light-emitting Diode display, but any number of Led???s may be used. Just adjust the circuitry properly. The Led display really does a number of things, it of program shows the general energy for the sign, but inaddition it shows the general environment regarding the attenuator. The Led display utilizes the LM3914 Led motorist. Select image to see bigger variation Take a moment to copy and printing This device is programmed to provide a sign for the input in a fashion that is linear. We plan it in to the Dot mode although the sign power appears to show in a club graph. When you look at the circuit the clock timer clamps the input at zero volts, then allows the sign fee a capacitor to your complete voltage. This is accomplished at an extremely higher rate, so it’s hidden to your attention. This indicates as a string of lit led???s utilizing the final anyone to be illuminated once the brightest. It is helpful at evening to exhibit the size of the display. Additionally at that time the sign is clamped to zero (gnd), the general voltage going to your attenuation circuit is shown as being a single brightly lit led. The environment of this attenuation level is scheduled by having a ten-turn pot, this may be a solitary change cooking pot, nevertheless the quality regarding the one change could be too abrupt.

The S-meter comes into cooking cooking cooking pot 3; this might be utilized to cut the full-scale voltage associated with the s-meter such that it corresponds to scale that is full the led meter.

This would go to a buffer amp, in order to perhaps maybe perhaps perhaps not load along 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 experiences 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 utilize the CMOS versions of this 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 perhaps 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, if it is perhaps not required. The TL084 is really a quad chip that is op-amp among the amps (pins 12,13,14) is employed as 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, once the true point where in actuality the attenuator will switch off, plus the top one determines at what degree the attenuator will start working. In involving the attenuation shall 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 into the reduced right part is 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 negative voltage converter 7662). The buffer amp can also drive an analog meter through the cooking pot 5 and 3K, if you would like. Additionally regarding 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 is certainly for the 751A Auto Attenuation Mods. Click photo to see bigger variation

You can expect to remember that lot significantly more than the four cables are coming in to the 751A. The reason being I had this mod for any other attenuators so might there be additional cables shown. I usually utilize additional cables for the ground sign, you do what you would like. We also work with a 10 conductor ribbon cable having a disconnect that is quick and so I can run radio stations minus the attenuator. Okay, in the left you will notice a tiny wire that is red this cable may be the +13.6 volts this is certainly switched using the on / off switch. It really is 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 package. Brown, Ebony, green, and Violet is attached with ground. The grey cable is from the attenuator package, to regulate the leading end gain associated with the 751A. It attaches to your foot of the 2N3904 transistor. Studying payday loans Massachusetts the circuit, a ferrite bead is employed through the emitter follower into the pre-amp phase. I do believe the others is quite clear. Don KF6GQ click image to see bigger variation Don KF6GQ