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Changing R227 is not a good idea because you will alter the rolloff caused by C225. Reducing R225 will give more gain without a noticable change in response because C223 is larger than needed. The low frequency corner is currently 4Hz; dropping R225 by half would double the gain and make the corner 8 Hz. It is also much easier to splice a new 820 ohm ...

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Figure 1. Close-up reveals a non-inverting amplifier. The gain of a non-inverting amplifier is given by $1 + \frac {R_f}{R_i}$. The simplest fix is to raise the value of Rf.

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The oldschool Vactrol uses an LDR which is a light dependant resister .The light source can be a led but in the old days it was incandescant like 6.3Volt 0.3 amp .The LDR is very linear and can take rather high voltages .Old large ones would take 100 Volts .This means that noise pickup was not a problem .Unfortunately these LDRs were made of Cadmium Sulphide ...

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The vactrol works as a gain-setting element for the op-amp. Gain will be 1+R15/R(vactrol). The more the LED light, the lower R(vactrol), and the higher the gain. Another way to do this is to use a voltage-controlled FET as an attennuator. Here is an EDN article describing how to do that: https://www.edn.com/a-guide-to-using-fets-for-voltage-controlled-...

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Curves in the left are two different presentations how the reflection factor seen by the feeding circuit depends on frequency. The yellow curve is the standing wave ratio which is calculated from the absolute value R of the reflection factor with formula SWR= (1+R)/(1-R). It's not measured directly, it's calculated. You should see that it's quite near 1 at 2,...

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To calculate voltage gain, you need to compute the value of Vo/Vs. Your circuit is divided into 2 main parts, one on the left (which has Vs) and one on the right (which has Vo). Looking at the right hand side, the value of every component is known except for Vbe which determines the magnitude of the current source. Vbe is found on the left side by using the ...

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The plots on the right are the antenna patterns at 3 different frequencies. The plot on the left looks like it's the measured S11 (input return loss), though the scale values don't make sense.

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