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August 25, 2024. More PNP Cirucits ~ A Nice IF Amp Stage

Continuing with our exploitation of PNP Transistor RF circuits we have one for you today. The 2N2907 and the 2N2905 are particularly good choices for PNP Transistors. Get the TO-18 style can for the 2N2907 so you can fit it with a heatsink -- they will be running hot for good IMD performance. For your dining and dancing pleasure a PNP RF/IF Amp stage.

For our PNP circuit we present an IF amp Stage as the input side to an IF Module that as that input stage can deliver 20dB or better over the range of 4 to 20MHz. It really shines at 9 MHz (24dB) for those often available 9 MHz Crystal Filters. A whole module and accounting for filter insertion loss (5dB) can delivering a whopping 35dB or more of gain overall.

I have set the matching transformer, so the output is looking at a 500 Ohm load (Filter Input). Therefore, we have 6 turns on the Primary side and 19 Turns on the Secondary. The transform is 19^2 = 361 and 6^2 = 36. Thusly, 361/36 = 10:1.

If by chance you brew up a Crystal Filter and you find that the Zin/out is 200 Ohms (fairly typical value) then you would need a 4:1 match, easily done with 4 Turns and 8 Turns (4^2 = 16 and 8^2 = 64 with 64/16 = 4:1).
 
 
2N2907 IF Stage
24dB Gain at 9 MHz


Observe the phasing on the matching transformer. You might find that the 2N2907 really runs hot with an 18 Ohm Emitter resistor so change R7 to 100 Ohms where the device will deliver a slightly less output but run a lot cooler.

On the output IF amp stage we have to match from 500 ohms (Filter Zout) to the input side of the 2nd amp and to the output side of the 2nd amp feeding an ADE-1 where we want 50 Ohms. 

Now this is a great exercise for those who have TIA tattooed on their foreheads and I leave that to you to figure out the component values. I personally have no desire to do that conversion. With the two amps and assuming a filter insertion loss of 5 dB we have a module capable of 35 dB (or more) of gain. This IF module would of course be relay steered in keeping with no Bitx or TIA amp circuits.

I hope to present a simulation of the output amp stage in a future blog along with a simulation of the whole IF Module.

Test out something different than a Bitx or TIA circuit and something different than a 2N3904 or 2N2222A. Here is your chance to be different.

TYGNYBNT

73's
Pete N6QW







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