Tech Notes

I have tried to leave as much technical jargon off my main pages. But for the sake of my readers who want a more detailed explanation I have decided to post this page. You got to this page by clicking on one of technical terms linked to this page. Under each article will be a button to click that will take you back where you came from.

TRF Circuitry

For those who don't recognize the abbreviation TRF means Tuned Radio Frequency. This type of circuit is not as sensitive because it is difficult to build enough gain (especially with the old tubes) and keep the stages from oscillating. You see the input and the output are on the same frequency. This of course takes extensive shielding and de-coupling all voltages. Also the older triode tubes had capacity between the grid, input and the output, the plate. There are circuits for neutralizing this capacity but when tuned to one frequency it was not good for another frequency.

The super-heterodyne, in contrast, mixed the incoming frequency with an oscillator frequency to produce a sum and difference frequency for the Intermediate Frequency (IF). This was chosen to be a lower frequency and easier to amplify and neutralize if necessary. The frequency stays the same no matter what the incoming frequency because the oscillating frequency is changed in step with the input frequency. This was very advanced and more complex than the TRF, but has greatly improved sensitivity. It of course has its problems, such as image frequency and tracking the oscillating with the incoming frequency.

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